planner.c

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/*-------------------------------------------------------------------------
 *
 * planner.c
 *    The query optimizer external interface.
 *
 * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/optimizer/plan/planner.c
 *
 *-------------------------------------------------------------------------
 */

#include "postgres.h"

#include <limits.h>
#include <math.h>

#include "access/genam.h"
#include "access/htup_details.h"
#include "access/parallel.h"
#include "access/sysattr.h"
#include "access/table.h"
#include "access/xact.h"
#include "catalog/pg_constraint.h"
#include "catalog/pg_inherits.h"
#include "catalog/pg_proc.h"
#include "catalog/pg_type.h"
#include "executor/executor.h"
#include "executor/nodeAgg.h"
#include "foreign/fdwapi.h"
#include "jit/jit.h"
#include "lib/bipartite_match.h"
#include "lib/knapsack.h"
#include "miscadmin.h"
#include "nodes/makefuncs.h"
#include "nodes/nodeFuncs.h"
#ifdef OPTIMIZER_DEBUG
#include "nodes/print.h"
#endif
#include "optimizer/appendinfo.h"
#include "optimizer/clauses.h"
#include "optimizer/cost.h"
#include "optimizer/inherit.h"
#include "optimizer/optimizer.h"
#include "optimizer/paramassign.h"
#include "optimizer/pathnode.h"
#include "optimizer/paths.h"
#include "optimizer/plancat.h"
#include "optimizer/planmain.h"
#include "optimizer/planner.h"
#include "optimizer/prep.h"
#include "optimizer/subselect.h"
#include "optimizer/tlist.h"
#include "parser/analyze.h"
#include "parser/parse_agg.h"
#include "parser/parsetree.h"
#include "partitioning/partdesc.h"
#include "rewrite/rewriteManip.h"
#include "storage/dsm_impl.h"
#include "utils/lsyscache.h"
#include "utils/rel.h"
#include "utils/selfuncs.h"
#include "utils/syscache.h"

/* GUC parameters */
double      cursor_tuple_fraction = DEFAULT_CURSOR_TUPLE_FRACTION;
int         force_parallel_mode = FORCE_PARALLEL_OFF;
bool        parallel_leader_participation = true;

/* Hook for plugins to get control in planner() */
planner_hook_type planner_hook = NULL;

/* Hook for plugins to get control when grouping_planner() plans upper rels */
create_upper_paths_hook_type create_upper_paths_hook = NULL;


/* Expression kind codes for preprocess_expression */
#define EXPRKIND_QUAL               0
#define EXPRKIND_TARGET             1
#define EXPRKIND_RTFUNC             2
#define EXPRKIND_RTFUNC_LATERAL     3
#define EXPRKIND_VALUES             4
#define EXPRKIND_VALUES_LATERAL     5
#define EXPRKIND_LIMIT              6
#define EXPRKIND_APPINFO            7
#define EXPRKIND_PHV                8
#define EXPRKIND_TABLESAMPLE        9
#define EXPRKIND_ARBITER_ELEM       10
#define EXPRKIND_TABLEFUNC          11
#define EXPRKIND_TABLEFUNC_LATERAL  12

/* Passthrough data for standard_qp_callback */
typedef struct
{
    List       *activeWindows;  /* active windows, if any */
    List       *groupClause;    /* overrides parse->groupClause */
} standard_qp_extra;

/*
 * Data specific to grouping sets
 */

typedef struct
{
    List       *rollups;
    List       *hash_sets_idx;
    double      dNumHashGroups;
    bool        any_hashable;
    Bitmapset  *unsortable_refs;
    Bitmapset  *unhashable_refs;
    List       *unsortable_sets;
    int        *tleref_to_colnum_map;
} grouping_sets_data;

/*
 * Temporary structure for use during WindowClause reordering in order to be
 * able to sort WindowClauses on partitioning/ordering prefix.
 */
typedef struct
{
    WindowClause *wc;
    List       *uniqueOrder;    /* A List of unique ordering/partitioning
                                 * clauses per Window */
} WindowClauseSortData;

/* Local functions */
static Node *preprocess_expression(PlannerInfo *root, Node *expr, int kind);
static void preprocess_qual_conditions(PlannerInfo *root, Node *jtnode);
static void grouping_planner(PlannerInfo *root, double tuple_fraction);
static grouping_sets_data *preprocess_grouping_sets(PlannerInfo *root);
static List *remap_to_groupclause_idx(List *groupClause, List *gsets,
                                      int *tleref_to_colnum_map);
static void preprocess_rowmarks(PlannerInfo *root);
static double preprocess_limit(PlannerInfo *root,
                               double tuple_fraction,
                               int64 *offset_est, int64 *count_est);
static void remove_useless_groupby_columns(PlannerInfo *root);
static List *preprocess_groupclause(PlannerInfo *root, List *force);
static List *extract_rollup_sets(List *groupingSets);
static List *reorder_grouping_sets(List *groupingSets, List *sortclause);
static void standard_qp_callback(PlannerInfo *root, void *extra);
static double get_number_of_groups(PlannerInfo *root,
                                   double path_rows,
                                   grouping_sets_data *gd,
                                   List *target_list);
static RelOptInfo *create_grouping_paths(PlannerInfo *root,
                                         RelOptInfo *input_rel,
                                         PathTarget *target,
                                         bool target_parallel_safe,
                                         grouping_sets_data *gd);
static bool is_degenerate_grouping(PlannerInfo *root);
static void create_degenerate_grouping_paths(PlannerInfo *root,
                                             RelOptInfo *input_rel,
                                             RelOptInfo *grouped_rel);
static RelOptInfo *make_grouping_rel(PlannerInfo *root, RelOptInfo *input_rel,
                                     PathTarget *target, bool target_parallel_safe,
                                     Node *havingQual);
static void create_ordinary_grouping_paths(PlannerInfo *root,
                                           RelOptInfo *input_rel,
                                           RelOptInfo *grouped_rel,
                                           const AggClauseCosts *agg_costs,
                                           grouping_sets_data *gd,
                                           GroupPathExtraData *extra,
                                           RelOptInfo **partially_grouped_rel_p);
static void consider_groupingsets_paths(PlannerInfo *root,
                                        RelOptInfo *grouped_rel,
                                        Path *path,
                                        bool is_sorted,
                                        bool can_hash,
                                        grouping_sets_data *gd,
                                        const AggClauseCosts *agg_costs,
                                        double dNumGroups);
static RelOptInfo *create_window_paths(PlannerInfo *root,
                                       RelOptInfo *input_rel,
                                       PathTarget *input_target,
                                       PathTarget *output_target,
                                       bool output_target_parallel_safe,
                                       WindowFuncLists *wflists,
                                       List *activeWindows);
static void create_one_window_path(PlannerInfo *root,
                                   RelOptInfo *window_rel,
                                   Path *path,
                                   PathTarget *input_target,
                                   PathTarget *output_target,
                                   WindowFuncLists *wflists,
                                   List *activeWindows);
static RelOptInfo *create_distinct_paths(PlannerInfo *root,
                                         RelOptInfo *input_rel);
static void create_partial_distinct_paths(PlannerInfo *root,
                                          RelOptInfo *input_rel,
                                          RelOptInfo *final_distinct_rel);
static RelOptInfo *create_final_distinct_paths(PlannerInfo *root,
                                               RelOptInfo *input_rel,
                                               RelOptInfo *distinct_rel);
static RelOptInfo *create_ordered_paths(PlannerInfo *root,
                                        RelOptInfo *input_rel,
                                        PathTarget *target,
                                        bool target_parallel_safe,
                                        double limit_tuples);
static PathTarget *make_group_input_target(PlannerInfo *root,
                                           PathTarget *final_target);
static PathTarget *make_partial_grouping_target(PlannerInfo *root,
                                                PathTarget *grouping_target,
                                                Node *havingQual);
static List *postprocess_setop_tlist(List *new_tlist, List *orig_tlist);
static List *select_active_windows(PlannerInfo *root, WindowFuncLists *wflists);
static PathTarget *make_window_input_target(PlannerInfo *root,
                                            PathTarget *final_target,
                                            List *activeWindows);
static List *make_pathkeys_for_window(PlannerInfo *root, WindowClause *wc,
                                      List *tlist);
static PathTarget *make_sort_input_target(PlannerInfo *root,
                                          PathTarget *final_target,
                                          bool *have_postponed_srfs);
static void adjust_paths_for_srfs(PlannerInfo *root, RelOptInfo *rel,
                                  List *targets, List *targets_contain_srfs);
static void add_paths_to_grouping_rel(PlannerInfo *root, RelOptInfo *input_rel,
                                      RelOptInfo *grouped_rel,
                                      RelOptInfo *partially_grouped_rel,
                                      const AggClauseCosts *agg_costs,
                                      grouping_sets_data *gd,
                                      double dNumGroups,
                                      GroupPathExtraData *extra);
static RelOptInfo *create_partial_grouping_paths(PlannerInfo *root,
                                                 RelOptInfo *grouped_rel,
                                                 RelOptInfo *input_rel,
                                                 grouping_sets_data *gd,
                                                 GroupPathExtraData *extra,
                                                 bool force_rel_creation);
static void gather_grouping_paths(PlannerInfo *root, RelOptInfo *rel);
static bool can_partial_agg(PlannerInfo *root);
static void apply_scanjoin_target_to_paths(PlannerInfo *root,
                                           RelOptInfo *rel,
                                           List *scanjoin_targets,
                                           List *scanjoin_targets_contain_srfs,
                                           bool scanjoin_target_parallel_safe,
                                           bool tlist_same_exprs);
static void create_partitionwise_grouping_paths(PlannerInfo *root,
                                                RelOptInfo *input_rel,
                                                RelOptInfo *grouped_rel,
                                                RelOptInfo *partially_grouped_rel,
                                                const AggClauseCosts *agg_costs,
                                                grouping_sets_data *gd,
                                                PartitionwiseAggregateType patype,
                                                GroupPathExtraData *extra);
static bool group_by_has_partkey(RelOptInfo *input_rel,
                                 List *targetList,
                                 List *groupClause);
static int  common_prefix_cmp(const void *a, const void *b);


/*****************************************************************************
 *
 *     Query optimizer entry point
 *
 * To support loadable plugins that monitor or modify planner behavior,
 * we provide a hook variable that lets a plugin get control before and
 * after the standard planning process.  The plugin would normally call
 * standard_planner().
 *
 * Note to plugin authors: standard_planner() scribbles on its Query input,
 * so you'd better copy that data structure if you want to plan more than once.
 *
 *****************************************************************************/
PlannedStmt *
planner(Query *parse, const char *query_string, int cursorOptions,
        ParamListInfo boundParams)
{
    PlannedStmt *result;

    if (planner_hook)
        result = (*planner_hook) (parse, query_string, cursorOptions, boundParams);
    else
        result = standard_planner(parse, query_string, cursorOptions, boundParams);
    return result;
}

PlannedStmt *
standard_planner(Query *parse, const char *query_string, int cursorOptions,
                 ParamListInfo boundParams)
{
    PlannedStmt *result;
    PlannerGlobal *glob;
    double      tuple_fraction;
    PlannerInfo *root;
    RelOptInfo *final_rel;
    Path       *best_path;
    Plan       *top_plan;
    ListCell   *lp,
               *lr;

    /*
     * Set up global state for this planner invocation.  This data is needed
     * across all levels of sub-Query that might exist in the given command,
     * so we keep it in a separate struct that's linked to by each per-Query
     * PlannerInfo.
     */
    glob = makeNode(PlannerGlobal);

    glob->boundParams = boundParams;
    glob->subplans = NIL;
    glob->subroots = NIL;
    glob->rewindPlanIDs = NULL;
    glob->finalrtable = NIL;
    glob->finalrowmarks = NIL;
    glob->resultRelations = NIL;
    glob->appendRelations = NIL;
    glob->relationOids = NIL;
    glob->invalItems = NIL;
    glob->paramExecTypes = NIL;
    glob->lastPHId = 0;
    glob->lastRowMarkId = 0;
    glob->lastPlanNodeId = 0;
    glob->transientPlan = false;
    glob->dependsOnRole = false;

    /*
     * Assess whether it's feasible to use parallel mode for this query. We
     * can't do this in a standalone backend, or if the command will try to
     * modify any data, or if this is a cursor operation, or if GUCs are set
     * to values that don't permit parallelism, or if parallel-unsafe
     * functions are present in the query tree.
     *
     * (Note that we do allow CREATE TABLE AS, SELECT INTO, and CREATE
     * MATERIALIZED VIEW to use parallel plans, but as of now, only the leader
     * backend writes into a completely new table.  In the future, we can
     * extend it to allow workers to write into the table.  However, to allow
     * parallel updates and deletes, we have to solve other problems,
     * especially around combo CIDs.)
     *
     * For now, we don't try to use parallel mode if we're running inside a
     * parallel worker.  We might eventually be able to relax this
     * restriction, but for now it seems best not to have parallel workers
     * trying to create their own parallel workers.
     */
    if ((cursorOptions & CURSOR_OPT_PARALLEL_OK) != 0 &&
        IsUnderPostmaster &&
        parse->commandType == CMD_SELECT &&
        !parse->hasModifyingCTE &&
        max_parallel_workers_per_gather > 0 &&
        !IsParallelWorker())
    {
        /* all the cheap tests pass, so scan the query tree */
        glob->maxParallelHazard = max_parallel_hazard(parse);
        glob->parallelModeOK = (glob->maxParallelHazard != PROPARALLEL_UNSAFE);
    }
    else
    {
        /* skip the query tree scan, just assume it's unsafe */
        glob->maxParallelHazard = PROPARALLEL_UNSAFE;
        glob->parallelModeOK = false;
    }

    /*
     * glob->parallelModeNeeded is normally set to false here and changed to
     * true during plan creation if a Gather or Gather Merge plan is actually
     * created (cf. create_gather_plan, create_gather_merge_plan).
     *
     * However, if force_parallel_mode = on or force_parallel_mode = regress,
     * then we impose parallel mode whenever it's safe to do so, even if the
     * final plan doesn't use parallelism.  It's not safe to do so if the
     * query contains anything parallel-unsafe; parallelModeOK will be false
     * in that case.  Note that parallelModeOK can't change after this point.
     * Otherwise, everything in the query is either parallel-safe or
     * parallel-restricted, and in either case it should be OK to impose
     * parallel-mode restrictions.  If that ends up breaking something, then
     * either some function the user included in the query is incorrectly
     * labeled as parallel-safe or parallel-restricted when in reality it's
     * parallel-unsafe, or else the query planner itself has a bug.
     */
    glob->parallelModeNeeded = glob->parallelModeOK &&
        (force_parallel_mode != FORCE_PARALLEL_OFF);

    /* Determine what fraction of the plan is likely to be scanned */
    if (cursorOptions & CURSOR_OPT_FAST_PLAN)
    {
        /*
         * We have no real idea how many tuples the user will ultimately FETCH
         * from a cursor, but it is often the case that he doesn't want 'em
         * all, or would prefer a fast-start plan anyway so that he can
         * process some of the tuples sooner.  Use a GUC parameter to decide
         * what fraction to optimize for.
         */
        tuple_fraction = cursor_tuple_fraction;

        /*
         * We document cursor_tuple_fraction as simply being a fraction, which
         * means the edge cases 0 and 1 have to be treated specially here.  We
         * convert 1 to 0 ("all the tuples") and 0 to a very small fraction.
         */
        if (tuple_fraction >= 1.0)
            tuple_fraction = 0.0;
        else if (tuple_fraction <= 0.0)
            tuple_fraction = 1e-10;
    }
    else
    {
        /* Default assumption is we need all the tuples */
        tuple_fraction = 0.0;
    }

    /* primary planning entry point (may recurse for subqueries) */
    root = subquery_planner(glob, parse, NULL,
                            false, tuple_fraction);

    /* Select best Path and turn it into a Plan */
    final_rel = fetch_upper_rel(root, UPPERREL_FINAL, NULL);
    best_path = get_cheapest_fractional_path(final_rel, tuple_fraction);

    top_plan = create_plan(root, best_path);

    /*
     * If creating a plan for a scrollable cursor, make sure it can run
     * backwards on demand.  Add a Material node at the top at need.
     */
    if (cursorOptions & CURSOR_OPT_SCROLL)
    {
        if (!ExecSupportsBackwardScan(top_plan))
            top_plan = materialize_finished_plan(top_plan);
    }

    /*
     * Optionally add a Gather node for testing purposes, provided this is
     * actually a safe thing to do.
     */
    if (force_parallel_mode != FORCE_PARALLEL_OFF && top_plan->parallel_safe)
    {
        Gather     *gather = makeNode(Gather);

        /*
         * If there are any initPlans attached to the formerly-top plan node,
         * move them up to the Gather node; same as we do for Material node in
         * materialize_finished_plan.
         */
        gather->plan.initPlan = top_plan->initPlan;
        top_plan->initPlan = NIL;

        gather->plan.targetlist = top_plan->targetlist;
        gather->plan.qual = NIL;
        gather->plan.lefttree = top_plan;
        gather->plan.righttree = NULL;
        gather->num_workers = 1;
        gather->single_copy = true;
        gather->invisible = (force_parallel_mode == FORCE_PARALLEL_REGRESS);

        /*
         * Since this Gather has no parallel-aware descendants to signal to,
         * we don't need a rescan Param.
         */
        gather->rescan_param = -1;

        /*
         * Ideally we'd use cost_gather here, but setting up dummy path data
         * to satisfy it doesn't seem much cleaner than knowing what it does.
         */
        gather->plan.startup_cost = top_plan->startup_cost +
            parallel_setup_cost;
        gather->plan.total_cost = top_plan->total_cost +
            parallel_setup_cost + parallel_tuple_cost * top_plan->plan_rows;
        gather->plan.plan_rows = top_plan->plan_rows;
        gather->plan.plan_width = top_plan->plan_width;
        gather->plan.parallel_aware = false;
        gather->plan.parallel_safe = false;

        /* use parallel mode for parallel plans. */
        root->glob->parallelModeNeeded = true;

        top_plan = &gather->plan;
    }

    /*
     * If any Params were generated, run through the plan tree and compute
     * each plan node's extParam/allParam sets.  Ideally we'd merge this into
     * set_plan_references' tree traversal, but for now it has to be separate
     * because we need to visit subplans before not after main plan.
     */
    if (glob->paramExecTypes != NIL)
    {
        Assert(list_length(glob->subplans) == list_length(glob->subroots));
        forboth(lp, glob->subplans, lr, glob->subroots)
        {
            Plan       *subplan = (Plan *) lfirst(lp);
            PlannerInfo *subroot = lfirst_node(PlannerInfo, lr);

            SS_finalize_plan(subroot, subplan);
        }
        SS_finalize_plan(root, top_plan);
    }

    /* final cleanup of the plan */
    Assert(glob->finalrtable == NIL);
    Assert(glob->finalrowmarks == NIL);
    Assert(glob->resultRelations == NIL);
    Assert(glob->appendRelations == NIL);
    top_plan = set_plan_references(root, top_plan);
    /* ... and the subplans (both regular subplans and initplans) */
    Assert(list_length(glob->subplans) == list_length(glob->subroots));
    forboth(lp, glob->subplans, lr, glob->subroots)
    {
        Plan       *subplan = (Plan *) lfirst(lp);
        PlannerInfo *subroot = lfirst_node(PlannerInfo, lr);

        lfirst(lp) = set_plan_references(subroot, subplan);
    }

    /* build the PlannedStmt result */
    result = makeNode(PlannedStmt);

    result->commandType = parse->commandType;
    result->queryId = parse->queryId;
    result->hasReturning = (parse->returningList != NIL);
    result->hasModifyingCTE = parse->hasModifyingCTE;
    result->canSetTag = parse->canSetTag;
    result->transientPlan = glob->transientPlan;
    result->dependsOnRole = glob->dependsOnRole;
    result->parallelModeNeeded = glob->parallelModeNeeded;
    result->planTree = top_plan;
    result->rtable = glob->finalrtable;
    result->resultRelations = glob->resultRelations;
    result->appendRelations = glob->appendRelations;
    result->subplans = glob->subplans;
    result->rewindPlanIDs = glob->rewindPlanIDs;
    result->rowMarks = glob->finalrowmarks;
    result->relationOids = glob->relationOids;
    result->invalItems = glob->invalItems;
    result->paramExecTypes = glob->paramExecTypes;
    /* utilityStmt should be null, but we might as well copy it */
    result->utilityStmt = parse->utilityStmt;
    result->stmt_location = parse->stmt_location;
    result->stmt_len = parse->stmt_len;

    result->jitFlags = PGJIT_NONE;
    if (jit_enabled && jit_above_cost >= 0 &&
        top_plan->total_cost > jit_above_cost)
    {
        result->jitFlags |= PGJIT_PERFORM;

        /*
         * Decide how much effort should be put into generating better code.
         */
        if (jit_optimize_above_cost >= 0 &&
            top_plan->total_cost > jit_optimize_above_cost)
            result->jitFlags |= PGJIT_OPT3;
        if (jit_inline_above_cost >= 0 &&
            top_plan->total_cost > jit_inline_above_cost)
            result->jitFlags |= PGJIT_INLINE;

        /*
         * Decide which operations should be JITed.
         */
        if (jit_expressions)
            result->jitFlags |= PGJIT_EXPR;
        if (jit_tuple_deforming)
            result->jitFlags |= PGJIT_DEFORM;
    }

    if (glob->partition_directory != NULL)
        DestroyPartitionDirectory(glob->partition_directory);

    return result;
}


/*--------------------
 * subquery_planner
 *    Invokes the planner on a subquery.  We recurse to here for each
 *    sub-SELECT found in the query tree.
 *
 * glob is the global state for the current planner run.
 * parse is the querytree produced by the parser & rewriter.
 * parent_root is the immediate parent Query's info (NULL at the top level).
 * hasRecursion is true if this is a recursive WITH query.
 * tuple_fraction is the fraction of tuples we expect will be retrieved.
 * tuple_fraction is interpreted as explained for grouping_planner, below.
 *
 * Basically, this routine does the stuff that should only be done once
 * per Query object.  It then calls grouping_planner.  At one time,
 * grouping_planner could be invoked recursively on the same Query object;
 * that's not currently true, but we keep the separation between the two
 * routines anyway, in case we need it again someday.
 *
 * subquery_planner will be called recursively to handle sub-Query nodes
 * found within the query's expressions and rangetable.
 *
 * Returns the PlannerInfo struct ("root") that contains all data generated
 * while planning the subquery.  In particular, the Path(s) attached to
 * the (UPPERREL_FINAL, NULL) upperrel represent our conclusions about the
 * cheapest way(s) to implement the query.  The top level will select the
 * best Path and pass it through createplan.c to produce a finished Plan.
 *--------------------
 */
PlannerInfo *
subquery_planner(PlannerGlobal *glob, Query *parse,
                 PlannerInfo *parent_root,
                 bool hasRecursion, double tuple_fraction)
{
    PlannerInfo *root;
    List       *newWithCheckOptions;
    List       *newHaving;
    bool        hasOuterJoins;
    bool        hasResultRTEs;
    RelOptInfo *final_rel;
    ListCell   *l;

    /* Create a PlannerInfo data structure for this subquery */
    root = makeNode(PlannerInfo);
    root->parse = parse;
    root->glob = glob;
    root->query_level = parent_root ? parent_root->query_level + 1 : 1;
    root->parent_root = parent_root;
    root->plan_params = NIL;
    root->outer_params = NULL;
    root->planner_cxt = CurrentMemoryContext;
    root->init_plans = NIL;
    root->cte_plan_ids = NIL;
    root->multiexpr_params = NIL;
    root->eq_classes = NIL;
    root->ec_merging_done = false;
    root->all_result_relids =
        parse->resultRelation ? bms_make_singleton(parse->resultRelation) : NULL;
    root->leaf_result_relids = NULL;    /* we'll find out leaf-ness later */
    root->append_rel_list = NIL;
    root->row_identity_vars = NIL;
    root->rowMarks = NIL;
    memset(root->upper_rels, 0, sizeof(root->upper_rels));
    memset(root->upper_targets, 0, sizeof(root->upper_targets));
    root->processed_tlist = NIL;
    root->update_colnos = NIL;
    root->grouping_map = NULL;
    root->minmax_aggs = NIL;
    root->qual_security_level = 0;
    root->hasPseudoConstantQuals = false;
    root->hasAlternativeSubPlans = false;
    root->hasRecursion = hasRecursion;
    if (hasRecursion)
        root->wt_param_id = assign_special_exec_param(root);
    else
        root->wt_param_id = -1;
    root->non_recursive_path = NULL;
    root->partColsUpdated = false;

    /*
     * If there is a WITH list, process each WITH query and either convert it
     * to RTE_SUBQUERY RTE(s) or build an initplan SubPlan structure for it.
     */
    if (parse->cteList)
        SS_process_ctes(root);

    /*
     * If the FROM clause is empty, replace it with a dummy RTE_RESULT RTE, so
     * that we don't need so many special cases to deal with that situation.
     */
    replace_empty_jointree(parse);

    /*
     * Look for ANY and EXISTS SubLinks in WHERE and JOIN/ON clauses, and try
     * to transform them into joins.  Note that this step does not descend
     * into subqueries; if we pull up any subqueries below, their SubLinks are
     * processed just before pulling them up.
     */
    if (parse->hasSubLinks)
        pull_up_sublinks(root);

    /*
     * Scan the rangetable for function RTEs, do const-simplification on them,
     * and then inline them if possible (producing subqueries that might get
     * pulled up next).  Recursion issues here are handled in the same way as
     * for SubLinks.
     */
    preprocess_function_rtes(root);

    /*
     * Check to see if any subqueries in the jointree can be merged into this
     * query.
     */
    pull_up_subqueries(root);

    /*
     * If this is a simple UNION ALL query, flatten it into an appendrel. We
     * do this now because it requires applying pull_up_subqueries to the leaf
     * queries of the UNION ALL, which weren't touched above because they
     * weren't referenced by the jointree (they will be after we do this).
     */
    if (parse->setOperations)
        flatten_simple_union_all(root);

    /*
     * Survey the rangetable to see what kinds of entries are present.  We can
     * skip some later processing if relevant SQL features are not used; for
     * example if there are no JOIN RTEs we can avoid the expense of doing
     * flatten_join_alias_vars().  This must be done after we have finished
     * adding rangetable entries, of course.  (Note: actually, processing of
     * inherited or partitioned rels can cause RTEs for their child tables to
     * get added later; but those must all be RTE_RELATION entries, so they
     * don't invalidate the conclusions drawn here.)
     */
    root->hasJoinRTEs = false;
    root->hasLateralRTEs = false;
    hasOuterJoins = false;
    hasResultRTEs = false;
    foreach(l, parse->rtable)
    {
        RangeTblEntry *rte = lfirst_node(RangeTblEntry, l);

        switch (rte->rtekind)
        {
            case RTE_RELATION:
                if (rte->inh)
                {
                    /*
                     * Check to see if the relation actually has any children;
                     * if not, clear the inh flag so we can treat it as a
                     * plain base relation.
                     *
                     * Note: this could give a false-positive result, if the
                     * rel once had children but no longer does.  We used to
                     * be able to clear rte->inh later on when we discovered
                     * that, but no more; we have to handle such cases as
                     * full-fledged inheritance.
                     */
                    rte->inh = has_subclass(rte->relid);
                }
                break;
            case RTE_JOIN:
                root->hasJoinRTEs = true;
                if (IS_OUTER_JOIN(rte->jointype))
                    hasOuterJoins = true;
                break;
            case RTE_RESULT:
                hasResultRTEs = true;
                break;
            default:
                /* No work here for other RTE types */
                break;
        }

        if (rte->lateral)
            root->hasLateralRTEs = true;

        /*
         * We can also determine the maximum security level required for any
         * securityQuals now.  Addition of inheritance-child RTEs won't affect
         * this, because child tables don't have their own securityQuals; see
         * expand_single_inheritance_child().
         */
        if (rte->securityQuals)
            root->qual_security_level = Max(root->qual_security_level,
                                            list_length(rte->securityQuals));
    }

    /*
     * If we have now verified that the query target relation is
     * non-inheriting, mark it as a leaf target.
     */
    if (parse->resultRelation)
    {
        RangeTblEntry *rte = rt_fetch(parse->resultRelation, parse->rtable);

        if (!rte->inh)
            root->leaf_result_relids =
                bms_make_singleton(parse->resultRelation);
    }

    /*
     * Preprocess RowMark information.  We need to do this after subquery
     * pullup, so that all base relations are present.
     */
    preprocess_rowmarks(root);

    /*
     * Set hasHavingQual to remember if HAVING clause is present.  Needed
     * because preprocess_expression will reduce a constant-true condition to
     * an empty qual list ... but "HAVING TRUE" is not a semantic no-op.
     */
    root->hasHavingQual = (parse->havingQual != NULL);

    /*
     * Do expression preprocessing on targetlist and quals, as well as other
     * random expressions in the querytree.  Note that we do not need to
     * handle sort/group expressions explicitly, because they are actually
     * part of the targetlist.
     */
    parse->targetList = (List *)
        preprocess_expression(root, (Node *) parse->targetList,
                              EXPRKIND_TARGET);

    /* Constant-folding might have removed all set-returning functions */
    if (parse->hasTargetSRFs)
        parse->hasTargetSRFs = expression_returns_set((Node *) parse->targetList);

    newWithCheckOptions = NIL;
    foreach(l, parse->withCheckOptions)
    {
        WithCheckOption *wco = lfirst_node(WithCheckOption, l);

        wco->qual = preprocess_expression(root, wco->qual,
                                          EXPRKIND_QUAL);
        if (wco->qual != NULL)
            newWithCheckOptions = lappend(newWithCheckOptions, wco);
    }
    parse->withCheckOptions = newWithCheckOptions;

    parse->returningList = (List *)
        preprocess_expression(root, (Node *) parse->returningList,
                              EXPRKIND_TARGET);

    preprocess_qual_conditions(root, (Node *) parse->jointree);

    parse->havingQual = preprocess_expression(root, parse->havingQual,
                                              EXPRKIND_QUAL);

    foreach(l, parse->windowClause)
    {
        WindowClause *wc = lfirst_node(WindowClause, l);

        /* partitionClause/orderClause are sort/group expressions */
        wc->startOffset = preprocess_expression(root, wc->startOffset,
                                                EXPRKIND_LIMIT);
        wc->endOffset = preprocess_expression(root, wc->endOffset,
                                              EXPRKIND_LIMIT);
    }

    parse->limitOffset = preprocess_expression(root, parse->limitOffset,
                                               EXPRKIND_LIMIT);
    parse->limitCount = preprocess_expression(root, parse->limitCount,
                                              EXPRKIND_LIMIT);

    if (parse->onConflict)
    {
        parse->onConflict->arbiterElems = (List *)
            preprocess_expression(root,
                                  (Node *) parse->onConflict->arbiterElems,
                                  EXPRKIND_ARBITER_ELEM);
        parse->onConflict->arbiterWhere =
            preprocess_expression(root,
                                  parse->onConflict->arbiterWhere,
                                  EXPRKIND_QUAL);
        parse->onConflict->onConflictSet = (List *)
            preprocess_expression(root,
                                  (Node *) parse->onConflict->onConflictSet,
                                  EXPRKIND_TARGET);
        parse->onConflict->onConflictWhere =
            preprocess_expression(root,
                                  parse->onConflict->onConflictWhere,
                                  EXPRKIND_QUAL);
        /* exclRelTlist contains only Vars, so no preprocessing needed */
    }

    root->append_rel_list = (List *)
        preprocess_expression(root, (Node *) root->append_rel_list,
                              EXPRKIND_APPINFO);

    /* Also need to preprocess expressions within RTEs */
    foreach(l, parse->rtable)
    {
        RangeTblEntry *rte = lfirst_node(RangeTblEntry, l);
        int         kind;
        ListCell   *lcsq;

        if (rte->rtekind == RTE_RELATION)
        {
            if (rte->tablesample)
                rte->tablesample = (TableSampleClause *)
                    preprocess_expression(root,
                                          (Node *) rte->tablesample,
                                          EXPRKIND_TABLESAMPLE);
        }
        else if (rte->rtekind == RTE_SUBQUERY)
        {
            /*
             * We don't want to do all preprocessing yet on the subquery's
             * expressions, since that will happen when we plan it.  But if it
             * contains any join aliases of our level, those have to get
             * expanded now, because planning of the subquery won't do it.
             * That's only possible if the subquery is LATERAL.
             */
            if (rte->lateral && root->hasJoinRTEs)
                rte->subquery = (Query *)
                    flatten_join_alias_vars(root->parse,
                                            (Node *) rte->subquery);
        }
        else if (rte->rtekind == RTE_FUNCTION)
        {
            /* Preprocess the function expression(s) fully */
            kind = rte->lateral ? EXPRKIND_RTFUNC_LATERAL : EXPRKIND_RTFUNC;
            rte->functions = (List *)
                preprocess_expression(root, (Node *) rte->functions, kind);
        }
        else if (rte->rtekind == RTE_TABLEFUNC)
        {
            /* Preprocess the function expression(s) fully */
            kind = rte->lateral ? EXPRKIND_TABLEFUNC_LATERAL : EXPRKIND_TABLEFUNC;
            rte->tablefunc = (TableFunc *)
                preprocess_expression(root, (Node *) rte->tablefunc, kind);
        }
        else if (rte->rtekind == RTE_VALUES)
        {
            /* Preprocess the values lists fully */
            kind = rte->lateral ? EXPRKIND_VALUES_LATERAL : EXPRKIND_VALUES;
            rte->values_lists = (List *)
                preprocess_expression(root, (Node *) rte->values_lists, kind);
        }

        /*
         * Process each element of the securityQuals list as if it were a
         * separate qual expression (as indeed it is).  We need to do it this
         * way to get proper canonicalization of AND/OR structure.  Note that
         * this converts each element into an implicit-AND sublist.
         */
        foreach(lcsq, rte->securityQuals)
        {
            lfirst(lcsq) = preprocess_expression(root,
                                                 (Node *) lfirst(lcsq),
                                                 EXPRKIND_QUAL);
        }
    }

    /*
     * Now that we are done preprocessing expressions, and in particular done
     * flattening join alias variables, get rid of the joinaliasvars lists.
     * They no longer match what expressions in the rest of the tree look
     * like, because we have not preprocessed expressions in those lists (and
     * do not want to; for example, expanding a SubLink there would result in
     * a useless unreferenced subplan).  Leaving them in place simply creates
     * a hazard for later scans of the tree.  We could try to prevent that by
     * using QTW_IGNORE_JOINALIASES in every tree scan done after this point,
     * but that doesn't sound very reliable.
     */
    if (root->hasJoinRTEs)
    {
        foreach(l, parse->rtable)
        {
            RangeTblEntry *rte = lfirst_node(RangeTblEntry, l);

            rte->joinaliasvars = NIL;
        }
    }

    /*
     * In some cases we may want to transfer a HAVING clause into WHERE. We
     * cannot do so if the HAVING clause contains aggregates (obviously) or
     * volatile functions (since a HAVING clause is supposed to be executed
     * only once per group).  We also can't do this if there are any nonempty
     * grouping sets; moving such a clause into WHERE would potentially change
     * the results, if any referenced column isn't present in all the grouping
     * sets.  (If there are only empty grouping sets, then the HAVING clause
     * must be degenerate as discussed below.)
     *
     * Also, it may be that the clause is so expensive to execute that we're
     * better off doing it only once per group, despite the loss of
     * selectivity.  This is hard to estimate short of doing the entire
     * planning process twice, so we use a heuristic: clauses containing
     * subplans are left in HAVING.  Otherwise, we move or copy the HAVING
     * clause into WHERE, in hopes of eliminating tuples before aggregation
     * instead of after.
     *
     * If the query has explicit grouping then we can simply move such a
     * clause into WHERE; any group that fails the clause will not be in the
     * output because none of its tuples will reach the grouping or
     * aggregation stage.  Otherwise we must have a degenerate (variable-free)
     * HAVING clause, which we put in WHERE so that query_planner() can use it
     * in a gating Result node, but also keep in HAVING to ensure that we
     * don't emit a bogus aggregated row. (This could be done better, but it
     * seems not worth optimizing.)
     *
     * Note that both havingQual and parse->jointree->quals are in
     * implicitly-ANDed-list form at this point, even though they are declared
     * as Node *.
     */
    newHaving = NIL;
    foreach(l, (List *) parse->havingQual)
    {
        Node       *havingclause = (Node *) lfirst(l);

        if ((parse->groupClause && parse->groupingSets) ||
            contain_agg_clause(havingclause) ||
            contain_volatile_functions(havingclause) ||
            contain_subplans(havingclause))
        {
            /* keep it in HAVING */
            newHaving = lappend(newHaving, havingclause);
        }
        else if (parse->groupClause && !parse->groupingSets)
        {
            /* move it to WHERE */
            parse->jointree->quals = (Node *)
                lappend((List *) parse->jointree->quals, havingclause);
        }
        else
        {
            /* put a copy in WHERE, keep it in HAVING */
            parse->jointree->quals = (Node *)
                lappend((List *) parse->jointree->quals,
                        copyObject(havingclause));
            newHaving = lappend(newHaving, havingclause);
        }
    }
    parse->havingQual = (Node *) newHaving;

    /* Remove any redundant GROUP BY columns */
    remove_useless_groupby_columns(root);

    /*
     * If we have any outer joins, try to reduce them to plain inner joins.
     * This step is most easily done after we've done expression
     * preprocessing.
     */
    if (hasOuterJoins)
        reduce_outer_joins(root);

    /*
     * If we have any RTE_RESULT relations, see if they can be deleted from
     * the jointree.  This step is most effectively done after we've done
     * expression preprocessing and outer join reduction.
     */
    if (hasResultRTEs)
        remove_useless_result_rtes(root);

    /*
     * Do the main planning.
     */
    grouping_planner(root, tuple_fraction);

    /*
     * Capture the set of outer-level param IDs we have access to, for use in
     * extParam/allParam calculations later.
     */
    SS_identify_outer_params(root);

    /*
     * If any initPlans were created in this query level, adjust the surviving
     * Paths' costs and parallel-safety flags to account for them.  The
     * initPlans won't actually get attached to the plan tree till
     * create_plan() runs, but we must include their effects now.
     */
    final_rel = fetch_upper_rel(root, UPPERREL_FINAL, NULL);
    SS_charge_for_initplans(root, final_rel);

    /*
     * Make sure we've identified the cheapest Path for the final rel.  (By
     * doing this here not in grouping_planner, we include initPlan costs in
     * the decision, though it's unlikely that will change anything.)
     */
    set_cheapest(final_rel);

    return root;
}

/*
 * preprocess_expression
 *      Do subquery_planner's preprocessing work for an expression,
 *      which can be a targetlist, a WHERE clause (including JOIN/ON
 *      conditions), a HAVING clause, or a few other things.
 */
static Node *
preprocess_expression(PlannerInfo *root, Node *expr, int kind)
{
    /*
     * Fall out quickly if expression is empty.  This occurs often enough to
     * be worth checking.  Note that null->null is the correct conversion for
     * implicit-AND result format, too.
     */
    if (expr == NULL)
        return NULL;

    /*
     * If the query has any join RTEs, replace join alias variables with
     * base-relation variables.  We must do this first, since any expressions
     * we may extract from the joinaliasvars lists have not been preprocessed.
     * For example, if we did this after sublink processing, sublinks expanded
     * out from join aliases would not get processed.  But we can skip this in
     * non-lateral RTE functions, VALUES lists, and TABLESAMPLE clauses, since
     * they can't contain any Vars of the current query level.
     */
    if (root->hasJoinRTEs &&
        !(kind == EXPRKIND_RTFUNC ||
          kind == EXPRKIND_VALUES ||
          kind == EXPRKIND_TABLESAMPLE ||
          kind == EXPRKIND_TABLEFUNC))
        expr = flatten_join_alias_vars(root->parse, expr);

    /*
     * Simplify constant expressions.  For function RTEs, this was already
     * done by preprocess_function_rtes ... but we have to do it again if the
     * RTE is LATERAL and might have contained join alias variables.
     *
     * Note: an essential effect of this is to convert named-argument function
     * calls to positional notation and insert the current actual values of
     * any default arguments for functions.  To ensure that happens, we *must*
     * process all expressions here.  Previous PG versions sometimes skipped
     * const-simplification if it didn't seem worth the trouble, but we can't
     * do that anymore.
     *
     * Note: this also flattens nested AND and OR expressions into N-argument
     * form.  All processing of a qual expression after this point must be
     * careful to maintain AND/OR flatness --- that is, do not generate a tree
     * with AND directly under AND, nor OR directly under OR.
     */
    if (!(kind == EXPRKIND_RTFUNC ||
          (kind == EXPRKIND_RTFUNC_LATERAL && !root->hasJoinRTEs)))
        expr = eval_const_expressions(root, expr);

    /*
     * If it's a qual or havingQual, canonicalize it.
     */
    if (kind == EXPRKIND_QUAL)
    {
        expr = (Node *) canonicalize_qual((Expr *) expr, false);

#ifdef OPTIMIZER_DEBUG
        printf("After canonicalize_qual()\n");
        pprint(expr);
#endif
    }

    /*
     * Check for ANY ScalarArrayOpExpr with Const arrays and set the
     * hashfuncid of any that might execute more quickly by using hash lookups
     * instead of a linear search.
     */
    if (kind == EXPRKIND_QUAL || kind == EXPRKIND_TARGET)
    {
        convert_saop_to_hashed_saop(expr);
    }

    /* Expand SubLinks to SubPlans */
    if (root->parse->hasSubLinks)
        expr = SS_process_sublinks(root, expr, (kind == EXPRKIND_QUAL));

    /*
     * XXX do not insert anything here unless you have grokked the comments in
     * SS_replace_correlation_vars ...
     */

    /* Replace uplevel vars with Param nodes (this IS possible in VALUES) */
    if (root->query_level > 1)
        expr = SS_replace_correlation_vars(root, expr);

    /*
     * If it's a qual or havingQual, convert it to implicit-AND format. (We
     * don't want to do this before eval_const_expressions, since the latter
     * would be unable to simplify a top-level AND correctly. Also,
     * SS_process_sublinks expects explicit-AND format.)
     */
    if (kind == EXPRKIND_QUAL)
        expr = (Node *) make_ands_implicit((Expr *) expr);

    return expr;
}

/*
 * preprocess_qual_conditions
 *      Recursively scan the query's jointree and do subquery_planner's
 *      preprocessing work on each qual condition found therein.
 */
static void
preprocess_qual_conditions(PlannerInfo *root, Node *jtnode)
{
    if (jtnode == NULL)
        return;
    if (IsA(jtnode, RangeTblRef))
    {
        /* nothing to do here */
    }
    else if (IsA(jtnode, FromExpr))
    {
        FromExpr   *f = (FromExpr *) jtnode;
        ListCell   *l;

        foreach(l, f->fromlist)
            preprocess_qual_conditions(root, lfirst(l));

        f->quals = preprocess_expression(root, f->quals, EXPRKIND_QUAL);
    }
    else if (IsA(jtnode, JoinExpr))
    {
        JoinExpr   *j = (JoinExpr *) jtnode;

        preprocess_qual_conditions(root, j->larg);
        preprocess_qual_conditions(root, j->rarg);

        j->quals = preprocess_expression(root, j->quals, EXPRKIND_QUAL);
    }
    else
        elog(ERROR, "unrecognized node type: %d",
             (int) nodeTag(jtnode));
}

/*
 * preprocess_phv_expression
 *    Do preprocessing on a PlaceHolderVar expression that's been pulled up.
 *
 * If a LATERAL subquery references an output of another subquery, and that
 * output must be wrapped in a PlaceHolderVar because of an intermediate outer
 * join, then we'll push the PlaceHolderVar expression down into the subquery
 * and later pull it back up during find_lateral_references, which runs after
 * subquery_planner has preprocessed all the expressions that were in the
 * current query level to start with.  So we need to preprocess it then.
 */
Expr *
preprocess_phv_expression(PlannerInfo *root, Expr *expr)
{
    return (Expr *) preprocess_expression(root, (Node *) expr, EXPRKIND_PHV);
}

/*--------------------
 * grouping_planner
 *    Perform planning steps related to grouping, aggregation, etc.
 *
 * This function adds all required top-level processing to the scan/join
 * Path(s) produced by query_planner.
 *
 * tuple_fraction is the fraction of tuples we expect will be retrieved.
 * tuple_fraction is interpreted as follows:
 *    0: expect all tuples to be retrieved (normal case)
 *    0 < tuple_fraction < 1: expect the given fraction of tuples available
 *      from the plan to be retrieved
 *    tuple_fraction >= 1: tuple_fraction is the absolute number of tuples
 *      expected to be retrieved (ie, a LIMIT specification)
 *
 * Returns nothing; the useful output is in the Paths we attach to the
 * (UPPERREL_FINAL, NULL) upperrel in *root.  In addition,
 * root->processed_tlist contains the final processed targetlist.
 *
 * Note that we have not done set_cheapest() on the final rel; it's convenient
 * to leave this to the caller.
 *--------------------
 */
static void
grouping_planner(PlannerInfo *root, double tuple_fraction)
{
    Query      *parse = root->parse;
    int64       offset_est = 0;
    int64       count_est = 0;
    double      limit_tuples = -1.0;
    bool        have_postponed_srfs = false;
    PathTarget *final_target;
    List       *final_targets;
    List       *final_targets_contain_srfs;
    bool        final_target_parallel_safe;
    RelOptInfo *current_rel;
    RelOptInfo *final_rel;
    FinalPathExtraData extra;
    ListCell   *lc;

    /* Tweak caller-supplied tuple_fraction if have LIMIT/OFFSET */
    if (parse->limitCount || parse->limitOffset)
    {
        tuple_fraction = preprocess_limit(root, tuple_fraction,
                                          &offset_est, &count_est);

        /*
         * If we have a known LIMIT, and don't have an unknown OFFSET, we can
         * estimate the effects of using a bounded sort.
         */
        if (count_est > 0 && offset_est >= 0)
            limit_tuples = (double) count_est + (double) offset_est;
    }

    /* Make tuple_fraction accessible to lower-level routines */
    root->tuple_fraction = tuple_fraction;

    if (parse->setOperations)
    {
        /*
         * If there's a top-level ORDER BY, assume we have to fetch all the
         * tuples.  This might be too simplistic given all the hackery below
         * to possibly avoid the sort; but the odds of accurate estimates here
         * are pretty low anyway.  XXX try to get rid of this in favor of
         * letting plan_set_operations generate both fast-start and
         * cheapest-total paths.
         */
        if (parse->sortClause)
            root->tuple_fraction = 0.0;

        /*
         * Construct Paths for set operations.  The results will not need any
         * work except perhaps a top-level sort and/or LIMIT.  Note that any
         * special work for recursive unions is the responsibility of
         * plan_set_operations.
         */
        current_rel = plan_set_operations(root);

        /*
         * We should not need to call preprocess_targetlist, since we must be
         * in a SELECT query node.  Instead, use the processed_tlist returned
         * by plan_set_operations (since this tells whether it returned any
         * resjunk columns!), and transfer any sort key information from the
         * original tlist.
         */
        Assert(parse->commandType == CMD_SELECT);

        /* for safety, copy processed_tlist instead of modifying in-place */
        root->processed_tlist =
            postprocess_setop_tlist(copyObject(root->processed_tlist),
                                    parse->targetList);

        /* Also extract the PathTarget form of the setop result tlist */
        final_target = current_rel->cheapest_total_path->pathtarget;

        /* And check whether it's parallel safe */
        final_target_parallel_safe =
            is_parallel_safe(root, (Node *) final_target->exprs);

        /* The setop result tlist couldn't contain any SRFs */
        Assert(!parse->hasTargetSRFs);
        final_targets = final_targets_contain_srfs = NIL;

        /*
         * Can't handle FOR [KEY] UPDATE/SHARE here (parser should have
         * checked already, but let's make sure).
         */
        if (parse->rowMarks)
            ereport(ERROR,
                    (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
            /*------
              translator: %s is a SQL row locking clause such as FOR UPDATE */
                     errmsg("%s is not allowed with UNION/INTERSECT/EXCEPT",
                            LCS_asString(linitial_node(RowMarkClause,
                                                       parse->rowMarks)->strength))));

        /*
         * Calculate pathkeys that represent result ordering requirements
         */
        Assert(parse->distinctClause == NIL);
        root->sort_pathkeys = make_pathkeys_for_sortclauses(root,
                                                            parse->sortClause,
                                                            root->processed_tlist);
    }
    else
    {
        /* No set operations, do regular planning */
        PathTarget *sort_input_target;
        List       *sort_input_targets;
        List       *sort_input_targets_contain_srfs;
        bool        sort_input_target_parallel_safe;
        PathTarget *grouping_target;
        List       *grouping_targets;
        List       *grouping_targets_contain_srfs;
        bool        grouping_target_parallel_safe;
        PathTarget *scanjoin_target;
        List       *scanjoin_targets;
        List       *scanjoin_targets_contain_srfs;
        bool        scanjoin_target_parallel_safe;
        bool        scanjoin_target_same_exprs;
        bool        have_grouping;
        WindowFuncLists *wflists = NULL;
        List       *activeWindows = NIL;
        grouping_sets_data *gset_data = NULL;
        standard_qp_extra qp_extra;

        /* A recursive query should always have setOperations */
        Assert(!root->hasRecursion);

        /* Preprocess grouping sets and GROUP BY clause, if any */
        if (parse->groupingSets)
        {
            gset_data = preprocess_grouping_sets(root);
        }
        else
        {
            /* Preprocess regular GROUP BY clause, if any */
            if (parse->groupClause)
                parse->groupClause = preprocess_groupclause(root, NIL);
        }

        /*
         * Preprocess targetlist.  Note that much of the remaining planning
         * work will be done with the PathTarget representation of tlists, but
         * we must also maintain the full representation of the final tlist so
         * that we can transfer its decoration (resnames etc) to the topmost
         * tlist of the finished Plan.  This is kept in processed_tlist.
         */
        preprocess_targetlist(root);

        /*
         * Mark all the aggregates with resolved aggtranstypes, and detect
         * aggregates that are duplicates or can share transition state.  We
         * must do this before slicing and dicing the tlist into various
         * pathtargets, else some copies of the Aggref nodes might escape
         * being marked.
         */
        if (parse->hasAggs)
        {
            preprocess_aggrefs(root, (Node *) root->processed_tlist);
            preprocess_aggrefs(root, (Node *) parse->havingQual);
        }

        /*
         * Locate any window functions in the tlist.  (We don't need to look
         * anywhere else, since expressions used in ORDER BY will be in there
         * too.)  Note that they could all have been eliminated by constant
         * folding, in which case we don't need to do any more work.
         */
        if (parse->hasWindowFuncs)
        {
            wflists = find_window_functions((Node *) root->processed_tlist,
                                            list_length(parse->windowClause));
            if (wflists->numWindowFuncs > 0)
                activeWindows = select_active_windows(root, wflists);
            else
                parse->hasWindowFuncs = false;
        }

        /*
         * Preprocess MIN/MAX aggregates, if any.  Note: be careful about
         * adding logic between here and the query_planner() call.  Anything
         * that is needed in MIN/MAX-optimizable cases will have to be
         * duplicated in planagg.c.
         */
        if (parse->hasAggs)
            preprocess_minmax_aggregates(root);

        /*
         * Figure out whether there's a hard limit on the number of rows that
         * query_planner's result subplan needs to return.  Even if we know a
         * hard limit overall, it doesn't apply if the query has any
         * grouping/aggregation operations, or SRFs in the tlist.
         */
        if (parse->groupClause ||
            parse->groupingSets ||
            parse->distinctClause ||
            parse->hasAggs ||
            parse->hasWindowFuncs ||
            parse->hasTargetSRFs ||
            root->hasHavingQual)
            root->limit_tuples = -1.0;
        else
            root->limit_tuples = limit_tuples;

        /* Set up data needed by standard_qp_callback */
        qp_extra.activeWindows = activeWindows;
        qp_extra.groupClause = (gset_data
                                ? (gset_data->rollups ? linitial_node(RollupData, gset_data->rollups)->groupClause : NIL)
                                : parse->groupClause);

        /*
         * Generate the best unsorted and presorted paths for the scan/join
         * portion of this Query, ie the processing represented by the
         * FROM/WHERE clauses.  (Note there may not be any presorted paths.)
         * We also generate (in standard_qp_callback) pathkey representations
         * of the query's sort clause, distinct clause, etc.
         */
        current_rel = query_planner(root, standard_qp_callback, &qp_extra);

        /*
         * Convert the query's result tlist into PathTarget format.
         *
         * Note: this cannot be done before query_planner() has performed
         * appendrel expansion, because that might add resjunk entries to
         * root->processed_tlist.  Waiting till afterwards is also helpful
         * because the target width estimates can use per-Var width numbers
         * that were obtained within query_planner().
         */
        final_target = create_pathtarget(root, root->processed_tlist);
        final_target_parallel_safe =
            is_parallel_safe(root, (Node *) final_target->exprs);

        /*
         * If ORDER BY was given, consider whether we should use a post-sort
         * projection, and compute the adjusted target for preceding steps if
         * so.
         */
        if (parse->sortClause)
        {
            sort_input_target = make_sort_input_target(root,
                                                       final_target,
                                                       &have_postponed_srfs);
            sort_input_target_parallel_safe =
                is_parallel_safe(root, (Node *) sort_input_target->exprs);
        }
        else
        {
            sort_input_target = final_target;
            sort_input_target_parallel_safe = final_target_parallel_safe;
        }

        /*
         * If we have window functions to deal with, the output from any
         * grouping step needs to be what the window functions want;
         * otherwise, it should be sort_input_target.
         */
        if (activeWindows)
        {
            grouping_target = make_window_input_target(root,
                                                       final_target,
                                                       activeWindows);
            grouping_target_parallel_safe =
                is_parallel_safe(root, (Node *) grouping_target->exprs);
        }
        else
        {
            grouping_target = sort_input_target;
            grouping_target_parallel_safe = sort_input_target_parallel_safe;
        }

        /*
         * If we have grouping or aggregation to do, the topmost scan/join
         * plan node must emit what the grouping step wants; otherwise, it
         * should emit grouping_target.
         */
        have_grouping = (parse->groupClause || parse->groupingSets ||
                         parse->hasAggs || root->hasHavingQual);
        if (have_grouping)
        {
            scanjoin_target = make_group_input_target(root, final_target);
            scanjoin_target_parallel_safe =
                is_parallel_safe(root, (Node *) scanjoin_target->exprs);
        }
        else
        {
            scanjoin_target = grouping_target;
            scanjoin_target_parallel_safe = grouping_target_parallel_safe;
        }

        /*
         * If there are any SRFs in the targetlist, we must separate each of
         * these PathTargets into SRF-computing and SRF-free targets.  Replace
         * each of the named targets with a SRF-free version, and remember the
         * list of additional projection steps we need to add afterwards.
         */
        if (parse->hasTargetSRFs)
        {
            /* final_target doesn't recompute any SRFs in sort_input_target */
            split_pathtarget_at_srfs(root, final_target, sort_input_target,
                                     &final_targets,
                                     &final_targets_contain_srfs);
            final_target = linitial_node(PathTarget, final_targets);
            Assert(!linitial_int(final_targets_contain_srfs));
            /* likewise for sort_input_target vs. grouping_target */
            split_pathtarget_at_srfs(root, sort_input_target, grouping_target,
                                     &sort_input_targets,
                                     &sort_input_targets_contain_srfs);
            sort_input_target = linitial_node(PathTarget, sort_input_targets);
            Assert(!linitial_int(sort_input_targets_contain_srfs));
            /* likewise for grouping_target vs. scanjoin_target */
            split_pathtarget_at_srfs(root, grouping_target, scanjoin_target,
                                     &grouping_targets,
                                     &grouping_targets_contain_srfs);
            grouping_target = linitial_node(PathTarget, grouping_targets);
            Assert(!linitial_int(grouping_targets_contain_srfs));
            /* scanjoin_target will not have any SRFs precomputed for it */
            split_pathtarget_at_srfs(root, scanjoin_target, NULL,
                                     &scanjoin_targets,
                                     &scanjoin_targets_contain_srfs);
            scanjoin_target = linitial_node(PathTarget, scanjoin_targets);
            Assert(!linitial_int(scanjoin_targets_contain_srfs));
        }
        else
        {
            /* initialize lists; for most of these, dummy values are OK */
            final_targets = final_targets_contain_srfs = NIL;
            sort_input_targets = sort_input_targets_contain_srfs = NIL;
            grouping_targets = grouping_targets_contain_srfs = NIL;
            scanjoin_targets = list_make1(scanjoin_target);
            scanjoin_targets_contain_srfs = NIL;
        }

        /* Apply scan/join target. */
        scanjoin_target_same_exprs = list_length(scanjoin_targets) == 1
            && equal(scanjoin_target->exprs, current_rel->reltarget->exprs);
        apply_scanjoin_target_to_paths(root, current_rel, scanjoin_targets,
                                       scanjoin_targets_contain_srfs,
                                       scanjoin_target_parallel_safe,
                                       scanjoin_target_same_exprs);

        /*
         * Save the various upper-rel PathTargets we just computed into
         * root->upper_targets[].  The core code doesn't use this, but it
         * provides a convenient place for extensions to get at the info.  For
         * consistency, we save all the intermediate targets, even though some
         * of the corresponding upperrels might not be needed for this query.
         */
        root->upper_targets[UPPERREL_FINAL] = final_target;
        root->upper_targets[UPPERREL_ORDERED] = final_target;
        root->upper_targets[UPPERREL_PARTIAL_DISTINCT] = sort_input_target;
        root->upper_targets[UPPERREL_DISTINCT] = sort_input_target;
        root->upper_targets[UPPERREL_WINDOW] = sort_input_target;
        root->upper_targets[UPPERREL_GROUP_AGG] = grouping_target;

        /*
         * If we have grouping and/or aggregation, consider ways to implement
         * that.  We build a new upperrel representing the output of this
         * phase.
         */
        if (have_grouping)
        {
            current_rel = create_grouping_paths(root,
                                                current_rel,
                                                grouping_target,
                                                grouping_target_parallel_safe,
                                                gset_data);
            /* Fix things up if grouping_target contains SRFs */
            if (parse->hasTargetSRFs)
                adjust_paths_for_srfs(root, current_rel,
                                      grouping_targets,
                                      grouping_targets_contain_srfs);
        }

        /*
         * If we have window functions, consider ways to implement those.  We
         * build a new upperrel representing the output of this phase.
         */
        if (activeWindows)
        {
            current_rel = create_window_paths(root,
                                              current_rel,
                                              grouping_target,
                                              sort_input_target,
                                              sort_input_target_parallel_safe,
                                              wflists,
                                              activeWindows);
            /* Fix things up if sort_input_target contains SRFs */
            if (parse->hasTargetSRFs)
                adjust_paths_for_srfs(root, current_rel,
                                      sort_input_targets,
                                      sort_input_targets_contain_srfs);
        }

        /*
         * If there is a DISTINCT clause, consider ways to implement that. We
         * build a new upperrel representing the output of this phase.
         */
        if (parse->distinctClause)
        {
            current_rel = create_distinct_paths(root,
                                                current_rel);
        }
    }                           /* end of if (setOperations) */

    /*
     * If ORDER BY was given, consider ways to implement that, and generate a
     * new upperrel containing only paths that emit the correct ordering and
     * project the correct final_target.  We can apply the original
     * limit_tuples limit in sort costing here, but only if there are no
     * postponed SRFs.
     */
    if (parse->sortClause)
    {
        current_rel = create_ordered_paths(root,
                                           current_rel,
                                           final_target,
                                           final_target_parallel_safe,
                                           have_postponed_srfs ? -1.0 :
                                           limit_tuples);
        /* Fix things up if final_target contains SRFs */
        if (parse->hasTargetSRFs)
            adjust_paths_for_srfs(root, current_rel,
                                  final_targets,
                                  final_targets_contain_srfs);
    }

    /*
     * Now we are prepared to build the final-output upperrel.
     */
    final_rel = fetch_upper_rel(root, UPPERREL_FINAL, NULL);

    /*
     * If the input rel is marked consider_parallel and there's nothing that's
     * not parallel-safe in the LIMIT clause, then the final_rel can be marked
     * consider_parallel as well.  Note that if the query has rowMarks or is
     * not a SELECT, consider_parallel will be false for every relation in the
     * query.
     */
    if (current_rel->consider_parallel &&
        is_parallel_safe(root, parse->limitOffset) &&
        is_parallel_safe(root, parse->limitCount))
        final_rel->consider_parallel = true;

    /*
     * If the current_rel belongs to a single FDW, so does the final_rel.
     */
    final_rel->serverid = current_rel->serverid;
    final_rel->userid = current_rel->userid;
    final_rel->useridiscurrent = current_rel->useridiscurrent;
    final_rel->fdwroutine = current_rel->fdwroutine;

    /*
     * Generate paths for the final_rel.  Insert all surviving paths, with
     * LockRows, Limit, and/or ModifyTable steps added if needed.
     */
    foreach(lc, current_rel->pathlist)
    {
        Path       *path = (Path *) lfirst(lc);

        /*
         * If there is a FOR [KEY] UPDATE/SHARE clause, add the LockRows node.
         * (Note: we intentionally test parse->rowMarks not root->rowMarks
         * here.  If there are only non-locking rowmarks, they should be
         * handled by the ModifyTable node instead.  However, root->rowMarks
         * is what goes into the LockRows node.)
         */
        if (parse->rowMarks)
        {
            path = (Path *) create_lockrows_path(root, final_rel, path,
                                                 root->rowMarks,
                                                 assign_special_exec_param(root));
        }

        /*
         * If there is a LIMIT/OFFSET clause, add the LIMIT node.
         */
        if (limit_needed(parse))
        {
            path = (Path *) create_limit_path(root, final_rel, path,
                                              parse->limitOffset,
                                              parse->limitCount,
                                              parse->limitOption,
                                              offset_est, count_est);
        }

        /*
         * If this is an INSERT/UPDATE/DELETE, add the ModifyTable node.
         */
        if (parse->commandType != CMD_SELECT)
        {
            Index       rootRelation;
            List       *resultRelations = NIL;
            List       *updateColnosLists = NIL;
            List       *withCheckOptionLists = NIL;
            List       *returningLists = NIL;
            List       *rowMarks;

            if (bms_membership(root->all_result_relids) == BMS_MULTIPLE)
            {
                /* Inherited UPDATE/DELETE */
                RelOptInfo *top_result_rel = find_base_rel(root,
                                                           parse->resultRelation);
                int         resultRelation = -1;

                /* Add only leaf children to ModifyTable. */
                while ((resultRelation = bms_next_member(root->leaf_result_relids,
                                                         resultRelation)) >= 0)
                {
                    RelOptInfo *this_result_rel = find_base_rel(root,
                                                                resultRelation);

                    /*
                     * Also exclude any leaf rels that have turned dummy since
                     * being added to the list, for example, by being excluded
                     * by constraint exclusion.
                     */
                    if (IS_DUMMY_REL(this_result_rel))
                        continue;

                    /* Build per-target-rel lists needed by ModifyTable */
                    resultRelations = lappend_int(resultRelations,
                                                  resultRelation);
                    if (parse->commandType == CMD_UPDATE)
                    {
                        List       *update_colnos = root->update_colnos;

                        if (this_result_rel != top_result_rel)
                            update_colnos =
                                adjust_inherited_attnums_multilevel(root,
                                                                    update_colnos,
                                                                    this_result_rel->relid,
                                                                    top_result_rel->relid);
                        updateColnosLists = lappend(updateColnosLists,
                                                    update_colnos);
                    }
                    if (parse->withCheckOptions)
                    {
                        List       *withCheckOptions = parse->withCheckOptions;

                        if (this_result_rel != top_result_rel)
                            withCheckOptions = (List *)
                                adjust_appendrel_attrs_multilevel(root,
                                                                  (Node *) withCheckOptions,
                                                                  this_result_rel->relids,
                                                                  top_result_rel->relids);
                        withCheckOptionLists = lappend(withCheckOptionLists,
                                                       withCheckOptions);
                    }
                    if (parse->returningList)
                    {
                        List       *returningList = parse->returningList;

                        if (this_result_rel != top_result_rel)
                            returningList = (List *)
                                adjust_appendrel_attrs_multilevel(root,
                                                                  (Node *) returningList,
                                                                  this_result_rel->relids,
                                                                  top_result_rel->relids);
                        returningLists = lappend(returningLists,
                                                 returningList);
                    }
                }

                if (resultRelations == NIL)
                {
                    /*
                     * We managed to exclude every child rel, so generate a
                     * dummy one-relation plan using info for the top target
                     * rel (even though that may not be a leaf target).
                     * Although it's clear that no data will be updated or
                     * deleted, we still need to have a ModifyTable node so
                     * that any statement triggers will be executed.  (This
                     * could be cleaner if we fixed nodeModifyTable.c to allow
                     * zero target relations, but that probably wouldn't be a
                     * net win.)
                     */
                    resultRelations = list_make1_int(parse->resultRelation);
                    if (parse->commandType == CMD_UPDATE)
                        updateColnosLists = list_make1(root->update_colnos);
                    if (parse->withCheckOptions)
                        withCheckOptionLists = list_make1(parse->withCheckOptions);
                    if (parse->returningList)
                        returningLists = list_make1(parse->returningList);
                }
            }
            else
            {
                /* Single-relation INSERT/UPDATE/DELETE. */
                resultRelations = list_make1_int(parse->resultRelation);
                if (parse->commandType == CMD_UPDATE)
                    updateColnosLists = list_make1(root->update_colnos);
                if (parse->withCheckOptions)
                    withCheckOptionLists = list_make1(parse->withCheckOptions);
                if (parse->returningList)
                    returningLists = list_make1(parse->returningList);
            }

            /*
             * If target is a partition root table, we need to mark the
             * ModifyTable node appropriately for that.
             */
            if (rt_fetch(parse->resultRelation, parse->rtable)->relkind ==
                RELKIND_PARTITIONED_TABLE)
                rootRelation = parse->resultRelation;
            else
                rootRelation = 0;

            /*
             * If there was a FOR [KEY] UPDATE/SHARE clause, the LockRows node
             * will have dealt with fetching non-locked marked rows, else we
             * need to have ModifyTable do that.
             */
            if (parse->rowMarks)
                rowMarks = NIL;
            else
                rowMarks = root->rowMarks;

            path = (Path *)
                create_modifytable_path(root, final_rel,
                                        path,
                                        parse->commandType,
                                        parse->canSetTag,
                                        parse->resultRelation,
                                        rootRelation,
                                        root->partColsUpdated,
                                        resultRelations,
                                        updateColnosLists,
                                        withCheckOptionLists,
                                        returningLists,
                                        rowMarks,
                                        parse->onConflict,
                                        assign_special_exec_param(root));
        }

        /* And shove it into final_rel */
        add_path(final_rel, path);
    }

    /*
     * Generate partial paths for final_rel, too, if outer query levels might
     * be able to make use of them.
     */
    if (final_rel->consider_parallel && root->query_level > 1 &&
        !limit_needed(parse))
    {
        Assert(!parse->rowMarks && parse->commandType == CMD_SELECT);
        foreach(lc, current_rel->partial_pathlist)
        {
            Path       *partial_path = (Path *) lfirst(lc);

            add_partial_path(final_rel, partial_path);
        }
    }

    extra.limit_needed = limit_needed(parse);
    extra.limit_tuples = limit_tuples;
    extra.count_est = count_est;
    extra.offset_est = offset_est;

    /*
     * If there is an FDW that's responsible for all baserels of the query,
     * let it consider adding ForeignPaths.
     */
    if (final_rel->fdwroutine &&
        final_rel->fdwroutine->GetForeignUpperPaths)
        final_rel->fdwroutine->GetForeignUpperPaths(root, UPPERREL_FINAL,
                                                    current_rel, final_rel,
                                                    &extra);

    /* Let extensions possibly add some more paths */
    if (create_upper_paths_hook)
        (*create_upper_paths_hook) (root, UPPERREL_FINAL,
                                    current_rel, final_rel, &extra);

    /* Note: currently, we leave it to callers to do set_cheapest() */
}

/*
 * Do preprocessing for groupingSets clause and related data.  This handles the
 * preliminary steps of expanding the grouping sets, organizing them into lists
 * of rollups, and preparing annotations which will later be filled in with
 * size estimates.
 */
static grouping_sets_data *
preprocess_grouping_sets(PlannerInfo *root)
{
    Query      *parse = root->parse;
    List       *sets;
    int         maxref = 0;
    ListCell   *lc;
    ListCell   *lc_set;
    grouping_sets_data *gd = palloc0(sizeof(grouping_sets_data));

    parse->groupingSets = expand_grouping_sets(parse->groupingSets, parse->groupDistinct, -1);

    gd->any_hashable = false;
    gd->unhashable_refs = NULL;
    gd->unsortable_refs = NULL;
    gd->unsortable_sets = NIL;

    if (parse->groupClause)
    {
        ListCell   *lc;

        foreach(lc, parse->groupClause)
        {
            SortGroupClause *gc = lfirst_node(SortGroupClause, lc);
            Index       ref = gc->tleSortGroupRef;

            if (ref > maxref)
                maxref = ref;

            if (!gc->hashable)
                gd->unhashable_refs = bms_add_member(gd->unhashable_refs, ref);

            if (!OidIsValid(gc->sortop))
                gd->unsortable_refs = bms_add_member(gd->unsortable_refs, ref);
        }
    }

    /* Allocate workspace array for remapping */
    gd->tleref_to_colnum_map = (int *) palloc((maxref + 1) * sizeof(int));

    /*
     * If we have any unsortable sets, we must extract them before trying to
     * prepare rollups. Unsortable sets don't go through
     * reorder_grouping_sets, so we must apply the GroupingSetData annotation
     * here.
     */
    if (!bms_is_empty(gd->unsortable_refs))
    {
        List       *sortable_sets = NIL;

        foreach(lc, parse->groupingSets)
        {
            List       *gset = (List *) lfirst(lc);

            if (bms_overlap_list(gd->unsortable_refs, gset))
            {
                GroupingSetData *gs = makeNode(GroupingSetData);

                gs->set = gset;
                gd->unsortable_sets = lappend(gd->unsortable_sets, gs);

                /*
                 * We must enforce here that an unsortable set is hashable;
                 * later code assumes this.  Parse analysis only checks that
                 * every individual column is either hashable or sortable.
                 *
                 * Note that passing this test doesn't guarantee we can
                 * generate a plan; there might be other showstoppers.
                 */
                if (bms_overlap_list(gd->unhashable_refs, gset))
                    ereport(ERROR,
                            (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                             errmsg("could not implement GROUP BY"),
                             errdetail("Some of the datatypes only support hashing, while others only support sorting.")));
            }
            else
                sortable_sets = lappend(sortable_sets, gset);
        }

        if (sortable_sets)
            sets = extract_rollup_sets(sortable_sets);
        else
            sets = NIL;
    }
    else
        sets = extract_rollup_sets(parse->groupingSets);

    foreach(lc_set, sets)
    {
        List       *current_sets = (List *) lfirst(lc_set);
        RollupData *rollup = makeNode(RollupData);
        GroupingSetData *gs;

        /*
         * Reorder the current list of grouping sets into correct prefix
         * order.  If only one aggregation pass is needed, try to make the
         * list match the ORDER BY clause; if more than one pass is needed, we
         * don't bother with that.
         *
         * Note that this reorders the sets from smallest-member-first to
         * largest-member-first, and applies the GroupingSetData annotations,
         * though the data will be filled in later.
         */
        current_sets = reorder_grouping_sets(current_sets,
                                             (list_length(sets) == 1
                                              ? parse->sortClause
                                              : NIL));

        /*
         * Get the initial (and therefore largest) grouping set.
         */
        gs = linitial_node(GroupingSetData, current_sets);

        /*
         * Order the groupClause appropriately.  If the first grouping set is
         * empty, then the groupClause must also be empty; otherwise we have
         * to force the groupClause to match that grouping set's order.
         *
         * (The first grouping set can be empty even though parse->groupClause
         * is not empty only if all non-empty grouping sets are unsortable.
         * The groupClauses for hashed grouping sets are built later on.)
         */
        if (gs->set)
            rollup->groupClause = preprocess_groupclause(root, gs->set);
        else
            rollup->groupClause = NIL;

        /*
         * Is it hashable? We pretend empty sets are hashable even though we
         * actually force them not to be hashed later. But don't bother if
         * there's nothing but empty sets (since in that case we can't hash
         * anything).
         */
        if (gs->set &&
            !bms_overlap_list(gd->unhashable_refs, gs->set))
        {
            rollup->hashable = true;
            gd->any_hashable = true;
        }

        /*
         * Now that we've pinned down an order for the groupClause for this
         * list of grouping sets, we need to remap the entries in the grouping
         * sets from sortgrouprefs to plain indices (0-based) into the
         * groupClause for this collection of grouping sets. We keep the
         * original form for later use, though.
         */
        rollup->gsets = remap_to_groupclause_idx(rollup->groupClause,
                                                 current_sets,
                                                 gd->tleref_to_colnum_map);
        rollup->gsets_data = current_sets;

        gd->rollups = lappend(gd->rollups, rollup);
    }

    if (gd->unsortable_sets)
    {
        /*
         * We have not yet pinned down a groupclause for this, but we will
         * need index-based lists for estimation purposes. Construct
         * hash_sets_idx based on the entire original groupclause for now.
         */
        gd->hash_sets_idx = remap_to_groupclause_idx(parse->groupClause,
                                                     gd->unsortable_sets,
                                                     gd->tleref_to_colnum_map);
        gd->any_hashable = true;
    }

    return gd;
}

/*
 * Given a groupclause and a list of GroupingSetData, return equivalent sets
 * (without annotation) mapped to indexes into the given groupclause.
 */
static List *
remap_to_groupclause_idx(List *groupClause,
                         List *gsets,
                         int *tleref_to_colnum_map)
{
    int         ref = 0;
    List       *result = NIL;
    ListCell   *lc;

    foreach(lc, groupClause)
    {
        SortGroupClause *gc = lfirst_node(SortGroupClause, lc);

        tleref_to_colnum_map[gc->tleSortGroupRef] = ref++;
    }

    foreach(lc, gsets)
    {
        List       *set = NIL;
        ListCell   *lc2;
        GroupingSetData *gs = lfirst_node(GroupingSetData, lc);

        foreach(lc2, gs->set)
        {
            set = lappend_int(set, tleref_to_colnum_map[lfirst_int(lc2)]);
        }

        result = lappend(result, set);
    }

    return result;
}


/*
 * preprocess_rowmarks - set up PlanRowMarks if needed
 */
static void
preprocess_rowmarks(PlannerInfo *root)
{
    Query      *parse = root->parse;
    Bitmapset  *rels;
    List       *prowmarks;
    ListCell   *l;
    int         i;

    if (parse->rowMarks)
    {
        /*
         * We've got trouble if FOR [KEY] UPDATE/SHARE appears inside
         * grouping, since grouping renders a reference to individual tuple
         * CTIDs invalid.  This is also checked at parse time, but that's
         * insufficient because of rule substitution, query pullup, etc.
         */
        CheckSelectLocking(parse, linitial_node(RowMarkClause,
                                                parse->rowMarks)->strength);
    }
    else
    {
        /*
         * We only need rowmarks for UPDATE, DELETE, or FOR [KEY]
         * UPDATE/SHARE.
         */
        if (parse->commandType != CMD_UPDATE &&
            parse->commandType != CMD_DELETE)
            return;
    }

    /*
     * We need to have rowmarks for all base relations except the target. We
     * make a bitmapset of all base rels and then remove the items we don't
     * need or have FOR [KEY] UPDATE/SHARE marks for.
     */
    rels = get_relids_in_jointree((Node *) parse->jointree, false);
    if (parse->resultRelation)
        rels = bms_del_member(rels, parse->resultRelation);

    /*
     * Convert RowMarkClauses to PlanRowMark representation.
     */
    prowmarks = NIL;
    foreach(l, parse->rowMarks)
    {
        RowMarkClause *rc = lfirst_node(RowMarkClause, l);
        RangeTblEntry *rte = rt_fetch(rc->rti, parse->rtable);
        PlanRowMark *newrc;

        /*
         * Currently, it is syntactically impossible to have FOR UPDATE et al
         * applied to an update/delete target rel.  If that ever becomes
         * possible, we should drop the target from the PlanRowMark list.
         */
        Assert(rc->rti != parse->resultRelation);

        /*
         * Ignore RowMarkClauses for subqueries; they aren't real tables and
         * can't support true locking.  Subqueries that got flattened into the
         * main query should be ignored completely.  Any that didn't will get
         * ROW_MARK_COPY items in the next loop.
         */
        if (rte->rtekind != RTE_RELATION)
            continue;

        rels = bms_del_member(rels, rc->rti);

        newrc = makeNode(PlanRowMark);
        newrc->rti = newrc->prti = rc->rti;
        newrc->rowmarkId = ++(root->glob->lastRowMarkId);
        newrc->markType = select_rowmark_type(rte, rc->strength);
        newrc->allMarkTypes = (1 << newrc->markType);
        newrc->strength = rc->strength;
        newrc->waitPolicy = rc->waitPolicy;
        newrc->isParent = false;

        prowmarks = lappend(prowmarks, newrc);
    }

    /*
     * Now, add rowmarks for any non-target, non-locked base relations.
     */
    i = 0;
    foreach(l, parse->rtable)
    {
        RangeTblEntry *rte = lfirst_node(RangeTblEntry, l);
        PlanRowMark *newrc;

        i++;
        if (!bms_is_member(i, rels))
            continue;

        newrc = makeNode(PlanRowMark);
        newrc->rti = newrc->prti = i;
        newrc->rowmarkId = ++(root->glob->lastRowMarkId);
        newrc->markType = select_rowmark_type(rte, LCS_NONE);
        newrc->allMarkTypes = (1 << newrc->markType);
        newrc->strength = LCS_NONE;
        newrc->waitPolicy = LockWaitBlock;  /* doesn't matter */
        newrc->isParent = false;

        prowmarks = lappend(prowmarks, newrc);
    }

    root->rowMarks = prowmarks;
}

/*
 * Select RowMarkType to use for a given table
 */
RowMarkType
select_rowmark_type(RangeTblEntry *rte, LockClauseStrength strength)
{
    if (rte->rtekind != RTE_RELATION)
    {
        /* If it's not a table at all, use ROW_MARK_COPY */
        return ROW_MARK_COPY;
    }
    else if (rte->relkind == RELKIND_FOREIGN_TABLE)
    {
        /* Let the FDW select the rowmark type, if it wants to */
        FdwRoutine *fdwroutine = GetFdwRoutineByRelId(rte->relid);

        if (fdwroutine->GetForeignRowMarkType != NULL)
            return fdwroutine->GetForeignRowMarkType(rte, strength);
        /* Otherwise, use ROW_MARK_COPY by default */
        return ROW_MARK_COPY;
    }
    else
    {
        /* Regular table, apply the appropriate lock type */
        switch (strength)
        {
            case LCS_NONE:

                /*
                 * We don't need a tuple lock, only the ability to re-fetch
                 * the row.
                 */
                return ROW_MARK_REFERENCE;
                break;
            case LCS_FORKEYSHARE:
                return ROW_MARK_KEYSHARE;
                break;
            case LCS_FORSHARE:
                return ROW_MARK_SHARE;
                break;
            case LCS_FORNOKEYUPDATE:
                return ROW_MARK_NOKEYEXCLUSIVE;
                break;
            case LCS_FORUPDATE:
                return ROW_MARK_EXCLUSIVE;
                break;
        }
        elog(ERROR, "unrecognized LockClauseStrength %d", (int) strength);
        return ROW_MARK_EXCLUSIVE;  /* keep compiler quiet */
    }
}

/*
 * preprocess_limit - do pre-estimation for LIMIT and/or OFFSET clauses
 *
 * We try to estimate the values of the LIMIT/OFFSET clauses, and pass the
 * results back in *count_est and *offset_est.  These variables are set to
 * 0 if the corresponding clause is not present, and -1 if it's present
 * but we couldn't estimate the value for it.  (The "0" convention is OK
 * for OFFSET but a little bit bogus for LIMIT: effectively we estimate
 * LIMIT 0 as though it were LIMIT 1.  But this is in line with the planner's
 * usual practice of never estimating less than one row.)  These values will
 * be passed to create_limit_path, which see if you change this code.
 *
 * The return value is the suitably adjusted tuple_fraction to use for
 * planning the query.  This adjustment is not overridable, since it reflects
 * plan actions that grouping_planner() will certainly take, not assumptions
 * about context.
 */
static double
preprocess_limit(PlannerInfo *root, double tuple_fraction,
                 int64 *offset_est, int64 *count_est)
{
    Query      *parse = root->parse;
    Node       *est;
    double      limit_fraction;

    /* Should not be called unless LIMIT or OFFSET */
    Assert(parse->limitCount || parse->limitOffset);

    /*
     * Try to obtain the clause values.  We use estimate_expression_value
     * primarily because it can sometimes do something useful with Params.
     */
    if (parse->limitCount)
    {
        est = estimate_expression_value(root, parse->limitCount);
        if (est && IsA(est, Const))
        {
            if (((Const *) est)->constisnull)
            {
                /* NULL indicates LIMIT ALL, ie, no limit */
                *count_est = 0; /* treat as not present */
            }
            else
            {
                *count_est = DatumGetInt64(((Const *) est)->constvalue);
                if (*count_est <= 0)
                    *count_est = 1; /* force to at least 1 */
            }
        }
        else
            *count_est = -1;    /* can't estimate */
    }
    else
        *count_est = 0;         /* not present */

    if (parse->limitOffset)
    {
        est = estimate_expression_value(root, parse->limitOffset);
        if (est && IsA(est, Const))
        {
            if (((Const *) est)->constisnull)
            {
                /* Treat NULL as no offset; the executor will too */
                *offset_est = 0;    /* treat as not present */
            }
            else
            {
                *offset_est = DatumGetInt64(((Const *) est)->constvalue);
                if (*offset_est < 0)
                    *offset_est = 0;    /* treat as not present */
            }
        }
        else
            *offset_est = -1;   /* can't estimate */
    }
    else
        *offset_est = 0;        /* not present */

    if (*count_est != 0)
    {
        /*
         * A LIMIT clause limits the absolute number of tuples returned.
         * However, if it's not a constant LIMIT then we have to guess; for
         * lack of a better idea, assume 10% of the plan's result is wanted.
         */
        if (*count_est < 0 || *offset_est < 0)
        {
            /* LIMIT or OFFSET is an expression ... punt ... */
            limit_fraction = 0.10;
        }
        else
        {
            /* LIMIT (plus OFFSET, if any) is max number of tuples needed */
            limit_fraction = (double) *count_est + (double) *offset_est;
        }

        /*
         * If we have absolute limits from both caller and LIMIT, use the
         * smaller value; likewise if they are both fractional.  If one is
         * fractional and the other absolute, we can't easily determine which
         * is smaller, but we use the heuristic that the absolute will usually
         * be smaller.
         */
        if (tuple_fraction >= 1.0)
        {
            if (limit_fraction >= 1.0)
            {
                /* both absolute */
                tuple_fraction = Min(tuple_fraction, limit_fraction);
            }
            else
            {
                /* caller absolute, limit fractional; use caller's value */
            }
        }
        else if (tuple_fraction > 0.0)
        {
            if (limit_fraction >= 1.0)
            {
                /* caller fractional, limit absolute; use limit */
                tuple_fraction = limit_fraction;
            }
            else
            {
                /* both fractional */
                tuple_fraction = Min(tuple_fraction, limit_fraction);
            }
        }
        else
        {
            /* no info from caller, just use limit */
            tuple_fraction = limit_fraction;
        }
    }
    else if (*offset_est != 0 && tuple_fraction > 0.0)
    {
        /*
         * We have an OFFSET but no LIMIT.  This acts entirely differently
         * from the LIMIT case: here, we need to increase rather than decrease
         * the caller's tuple_fraction, because the OFFSET acts to cause more
         * tuples to be fetched instead of fewer.  This only matters if we got
         * a tuple_fraction > 0, however.
         *
         * As above, use 10% if OFFSET is present but unestimatable.
         */
        if (*offset_est < 0)
            limit_fraction = 0.10;
        else
            limit_fraction = (double) *offset_est;

        /*
         * If we have absolute counts from both caller and OFFSET, add them
         * together; likewise if they are both fractional.  If one is
         * fractional and the other absolute, we want to take the larger, and
         * we heuristically assume that's the fractional one.
         */
        if (tuple_fraction >= 1.0)
        {
            if (limit_fraction >= 1.0)
            {
                /* both absolute, so add them together */
                tuple_fraction += limit_fraction;
            }
            else
            {
                /* caller absolute, limit fractional; use limit */
                tuple_fraction = limit_fraction;
            }
        }
        else
        {
            if (limit_fraction >= 1.0)
            {
                /* caller fractional, limit absolute; use caller's value */
            }
            else
            {
                /* both fractional, so add them together */
                tuple_fraction += limit_fraction;
                if (tuple_fraction >= 1.0)
                    tuple_fraction = 0.0;   /* assume fetch all */
            }
        }
    }

    return tuple_fraction;
}

/*
 * limit_needed - do we actually need a Limit plan node?
 *
 * If we have constant-zero OFFSET and constant-null LIMIT, we can skip adding
 * a Limit node.  This is worth checking for because "OFFSET 0" is a common
 * locution for an optimization fence.  (Because other places in the planner
 * merely check whether parse->limitOffset isn't NULL, it will still work as
 * an optimization fence --- we're just suppressing unnecessary run-time
 * overhead.)
 *
 * This might look like it could be merged into preprocess_limit, but there's
 * a key distinction: here we need hard constants in OFFSET/LIMIT, whereas
 * in preprocess_limit it's good enough to consider estimated values.
 */
bool
limit_needed(Query *parse)
{
    Node       *node;

    node = parse->limitCount;
    if (node)
    {
        if (IsA(node, Const))
        {
            /* NULL indicates LIMIT ALL, ie, no limit */
            if (!((Const *) node)->constisnull)
                return true;    /* LIMIT with a constant value */
        }
        else
            return true;        /* non-constant LIMIT */
    }

    node = parse->limitOffset;
    if (node)
    {
        if (IsA(node, Const))
        {
            /* Treat NULL as no offset; the executor would too */
            if (!((Const *) node)->constisnull)
            {
                int64       offset = DatumGetInt64(((Const *) node)->constvalue);

                if (offset != 0)
                    return true;    /* OFFSET with a nonzero value */
            }
        }
        else
            return true;        /* non-constant OFFSET */
    }

    return false;               /* don't need a Limit plan node */
}


/*
 * remove_useless_groupby_columns
 *      Remove any columns in the GROUP BY clause that are redundant due to
 *      being functionally dependent on other GROUP BY columns.
 *
 * Since some other DBMSes do not allow references to ungrouped columns, it's
 * not unusual to find all columns listed in GROUP BY even though listing the
 * primary-key columns would be sufficient.  Deleting such excess columns
 * avoids redundant sorting work, so it's worth doing.
 *
 * Relcache invalidations will ensure that cached plans become invalidated
 * when the underlying index of the pkey constraint is dropped.
 *
 * Currently, we only make use of pkey constraints for this, however, we may
 * wish to take this further in the future and also use unique constraints
 * which have NOT NULL columns.  In that case, plan invalidation will still
 * work since relations will receive a relcache invalidation when a NOT NULL
 * constraint is dropped.
 */
static void
remove_useless_groupby_columns(PlannerInfo *root)
{
    Query      *parse = root->parse;
    Bitmapset **groupbyattnos;
    Bitmapset **surplusvars;
    ListCell   *lc;
    int         relid;

    /* No chance to do anything if there are less than two GROUP BY items */
    if (list_length(parse->groupClause) < 2)
        return;

    /* Don't fiddle with the GROUP BY clause if the query has grouping sets */
    if (parse->groupingSets)
        return;

    /*
     * Scan the GROUP BY clause to find GROUP BY items that are simple Vars.
     * Fill groupbyattnos[k] with a bitmapset of the column attnos of RTE k
     * that are GROUP BY items.
     */
    groupbyattnos = (Bitmapset **) palloc0(sizeof(Bitmapset *) *
                                           (list_length(parse->rtable) + 1));
    foreach(lc, parse->groupClause)
    {
        SortGroupClause *sgc = lfirst_node(SortGroupClause, lc);
        TargetEntry *tle = get_sortgroupclause_tle(sgc, parse->targetList);
        Var        *var = (Var *) tle->expr;

        /*
         * Ignore non-Vars and Vars from other query levels.
         *
         * XXX in principle, stable expressions containing Vars could also be
         * removed, if all the Vars are functionally dependent on other GROUP
         * BY items.  But it's not clear that such cases occur often enough to
         * be worth troubling over.
         */
        if (!IsA(var, Var) ||
            var->varlevelsup > 0)
            continue;

        /* OK, remember we have this Var */
        relid = var->varno;
        Assert(relid <= list_length(parse->rtable));
        groupbyattnos[relid] = bms_add_member(groupbyattnos[relid],
                                              var->varattno - FirstLowInvalidHeapAttributeNumber);
    }

    /*
     * Consider each relation and see if it is possible to remove some of its
     * Vars from GROUP BY.  For simplicity and speed, we do the actual removal
     * in a separate pass.  Here, we just fill surplusvars[k] with a bitmapset
     * of the column attnos of RTE k that are removable GROUP BY items.
     */
    surplusvars = NULL;         /* don't allocate array unless required */
    relid = 0;
    foreach(lc, parse->rtable)
    {
        RangeTblEntry *rte = lfirst_node(RangeTblEntry, lc);
        Bitmapset  *relattnos;
        Bitmapset  *pkattnos;
        Oid         constraintOid;

        relid++;

        /* Only plain relations could have primary-key constraints */
        if (rte->rtekind != RTE_RELATION)
            continue;

        /*
         * We must skip inheritance parent tables as some of the child rels
         * may cause duplicate rows.  This cannot happen with partitioned
         * tables, however.
         */
        if (rte->inh && rte->relkind != RELKIND_PARTITIONED_TABLE)
            continue;

        /* Nothing to do unless this rel has multiple Vars in GROUP BY */
        relattnos = groupbyattnos[relid];
        if (bms_membership(relattnos) != BMS_MULTIPLE)
            continue;

        /*
         * Can't remove any columns for this rel if there is no suitable
         * (i.e., nondeferrable) primary key constraint.
         */
        pkattnos = get_primary_key_attnos(rte->relid, false, &constraintOid);
        if (pkattnos == NULL)
            continue;

        /*
         * If the primary key is a proper subset of relattnos then we have
         * some items in the GROUP BY that can be removed.
         */
        if (bms_subset_compare(pkattnos, relattnos) == BMS_SUBSET1)
        {
            /*
             * To easily remember whether we've found anything to do, we don't
             * allocate the surplusvars[] array until we find something.
             */
            if (surplusvars == NULL)
                surplusvars = (Bitmapset **) palloc0(sizeof(Bitmapset *) *
                                                     (list_length(parse->rtable) + 1));

            /* Remember the attnos of the removable columns */
            surplusvars[relid] = bms_difference(relattnos, pkattnos);
        }
    }

    /*
     * If we found any surplus Vars, build a new GROUP BY clause without them.
     * (Note: this may leave some TLEs with unreferenced ressortgroupref
     * markings, but that's harmless.)
     */
    if (surplusvars != NULL)
    {
        List       *new_groupby = NIL;

        foreach(lc, parse->groupClause)
        {
            SortGroupClause *sgc = lfirst_node(SortGroupClause, lc);
            TargetEntry *tle = get_sortgroupclause_tle(sgc, parse->targetList);
            Var        *var = (Var *) tle->expr;

            /*
             * New list must include non-Vars, outer Vars, and anything not
             * marked as surplus.
             */
            if (!IsA(var, Var) ||
                var->varlevelsup > 0 ||
                !bms_is_member(var->varattno - FirstLowInvalidHeapAttributeNumber,
                               surplusvars[var->varno]))
                new_groupby = lappend(new_groupby, sgc);
        }

        parse->groupClause = new_groupby;
    }
}

/*
 * preprocess_groupclause - do preparatory work on GROUP BY clause
 *
 * The idea here is to adjust the ordering of the GROUP BY elements
 * (which in itself is semantically insignificant) to match ORDER BY,
 * thereby allowing a single sort operation to both implement the ORDER BY
 * requirement and set up for a Unique step that implements GROUP BY.
 *
 * In principle it might be interesting to consider other orderings of the
 * GROUP BY elements, which could match the sort ordering of other
 * possible plans (eg an indexscan) and thereby reduce cost.  We don't
 * bother with that, though.  Hashed grouping will frequently win anyway.
 *
 * Note: we need no comparable processing of the distinctClause because
 * the parser already enforced that that matches ORDER BY.
 *
 * For grouping sets, the order of items is instead forced to agree with that
 * of the grouping set (and items not in the grouping set are skipped). The
 * work of sorting the order of grouping set elements to match the ORDER BY if
 * possible is done elsewhere.
 */
static List *
preprocess_groupclause(PlannerInfo *root, List *force)
{
    Query      *parse = root->parse;
    List       *new_groupclause = NIL;
    bool        partial_match;
    ListCell   *sl;
    ListCell   *gl;

    /* For grouping sets, we need to force the ordering */
    if (force)
    {
        foreach(sl, force)
        {
            Index       ref = lfirst_int(sl);
            SortGroupClause *cl = get_sortgroupref_clause(ref, parse->groupClause);

            new_groupclause = lappend(new_groupclause, cl);
        }

        return new_groupclause;
    }

    /* If no ORDER BY, nothing useful to do here */
    if (parse->sortClause == NIL)
        return parse->groupClause;

    /*
     * Scan the ORDER BY clause and construct a list of matching GROUP BY
     * items, but only as far as we can make a matching prefix.
     *
     * This code assumes that the sortClause contains no duplicate items.
     */
    foreach(sl, parse->sortClause)
    {
        SortGroupClause *sc = lfirst_node(SortGroupClause, sl);

        foreach(gl, parse->groupClause)
        {
            SortGroupClause *gc = lfirst_node(SortGroupClause, gl);

            if (equal(gc, sc))
            {
                new_groupclause = lappend(new_groupclause, gc);
                break;
            }
        }
        if (gl == NULL)
            break;              /* no match, so stop scanning */
    }

    /* Did we match all of the ORDER BY list, or just some of it? */
    partial_match = (sl != NULL);

    /* If no match at all, no point in reordering GROUP BY */
    if (new_groupclause == NIL)
        return parse->groupClause;

    /*
     * Add any remaining GROUP BY items to the new list, but only if we were
     * able to make a complete match.  In other words, we only rearrange the
     * GROUP BY list if the result is that one list is a prefix of the other
     * --- otherwise there's no possibility of a common sort.  Also, give up
     * if there are any non-sortable GROUP BY items, since then there's no
     * hope anyway.
     */
    foreach(gl, parse->groupClause)
    {
        SortGroupClause *gc = lfirst_node(SortGroupClause, gl);

        if (list_member_ptr(new_groupclause, gc))
            continue;           /* it matched an ORDER BY item */
        if (partial_match)
            return parse->groupClause;  /* give up, no common sort possible */
        if (!OidIsValid(gc->sortop))
            return parse->groupClause;  /* give up, GROUP BY can't be sorted */
        new_groupclause = lappend(new_groupclause, gc);
    }

    /* Success --- install the rearranged GROUP BY list */
    Assert(list_length(parse->groupClause) == list_length(new_groupclause));
    return new_groupclause;
}

/*
 * Extract lists of grouping sets that can be implemented using a single
 * rollup-type aggregate pass each. Returns a list of lists of grouping sets.
 *
 * Input must be sorted with smallest sets first. Result has each sublist
 * sorted with smallest sets first.
 *
 * We want to produce the absolute minimum possible number of lists here to
 * avoid excess sorts. Fortunately, there is an algorithm for this; the problem
 * of finding the minimal partition of a partially-ordered set into chains
 * (which is what we need, taking the list of grouping sets as a poset ordered
 * by set inclusion) can be mapped to the problem of finding the maximum
 * cardinality matching on a bipartite graph, which is solvable in polynomial
 * time with a worst case of no worse than O(n^2.5) and usually much
 * better. Since our N is at most 4096, we don't need to consider fallbacks to
 * heuristic or approximate methods.  (Planning time for a 12-d cube is under
 * half a second on my modest system even with optimization off and assertions
 * on.)
 */
static List *
extract_rollup_sets(List *groupingSets)
{
    int         num_sets_raw = list_length(groupingSets);
    int         num_empty = 0;
    int         num_sets = 0;   /* distinct sets */
    int         num_chains = 0;
    List       *result = NIL;
    List      **results;
    List      **orig_sets;
    Bitmapset **set_masks;
    int        *chains;
    short     **adjacency;
    short      *adjacency_buf;
    BipartiteMatchState *state;
    int         i;
    int         j;
    int         j_size;
    ListCell   *lc1 = list_head(groupingSets);
    ListCell   *lc;

    /*
     * Start by stripping out empty sets.  The algorithm doesn't require this,
     * but the planner currently needs all empty sets to be returned in the
     * first list, so we strip them here and add them back after.
     */
    while (lc1 && lfirst(lc1) == NIL)
    {
        ++num_empty;
        lc1 = lnext(groupingSets, lc1);
    }

    /* bail out now if it turns out that all we had were empty sets. */
    if (!lc1)
        return list_make1(groupingSets);

    /*----------
     * We don't strictly need to remove duplicate sets here, but if we don't,
     * they tend to become scattered through the result, which is a bit
     * confusing (and irritating if we ever decide to optimize them out).
     * So we remove them here and add them back after.
     *
     * For each non-duplicate set, we fill in the following:
     *
     * orig_sets[i] = list of the original set lists
     * set_masks[i] = bitmapset for testing inclusion
     * adjacency[i] = array [n, v1, v2, ... vn] of adjacency indices
     *
     * chains[i] will be the result group this set is assigned to.
     *
     * We index all of these from 1 rather than 0 because it is convenient
     * to leave 0 free for the NIL node in the graph algorithm.
     *----------
     */
    orig_sets = palloc0((num_sets_raw + 1) * sizeof(List *));
    set_masks = palloc0((num_sets_raw + 1) * sizeof(Bitmapset *));
    adjacency = palloc0((num_sets_raw + 1) * sizeof(short *));
    adjacency_buf = palloc((num_sets_raw + 1) * sizeof(short));

    j_size = 0;
    j = 0;
    i = 1;

    for_each_cell(lc, groupingSets, lc1)
    {
        List       *candidate = (List *) lfirst(lc);
        Bitmapset  *candidate_set = NULL;
        ListCell   *lc2;
        int         dup_of = 0;

        foreach(lc2, candidate)
        {
            candidate_set = bms_add_member(candidate_set, lfirst_int(lc2));
        }

        /* we can only be a dup if we're the same length as a previous set */
        if (j_size == list_length(candidate))
        {
            int         k;

            for (k = j; k < i; ++k)
            {
                if (bms_equal(set_masks[k], candidate_set))
                {
                    dup_of = k;
                    break;
                }
            }
        }
        else if (j_size < list_length(candidate))
        {
            j_size = list_length(candidate);
            j = i;
        }

        if (dup_of > 0)
        {
            orig_sets[dup_of] = lappend(orig_sets[dup_of], candidate);
            bms_free(candidate_set);
        }
        else
        {
            int         k;
            int         n_adj = 0;

            orig_sets[i] = list_make1(candidate);
            set_masks[i] = candidate_set;

            /* fill in adjacency list; no need to compare equal-size sets */

            for (k = j - 1; k > 0; --k)
            {
                if (bms_is_subset(set_masks[k], candidate_set))
                    adjacency_buf[++n_adj] = k;
            }

            if (n_adj > 0)
            {
                adjacency_buf[0] = n_adj;
                adjacency[i] = palloc((n_adj + 1) * sizeof(short));
                memcpy(adjacency[i], adjacency_buf, (n_adj + 1) * sizeof(short));
            }
            else
                adjacency[i] = NULL;

            ++i;
        }
    }

    num_sets = i - 1;

    /*
     * Apply the graph matching algorithm to do the work.
     */
    state = BipartiteMatch(num_sets, num_sets, adjacency);

    /*
     * Now, the state->pair* fields have the info we need to assign sets to
     * chains. Two sets (u,v) belong to the same chain if pair_uv[u] = v or
     * pair_vu[v] = u (both will be true, but we check both so that we can do
     * it in one pass)
     */
    chains = palloc0((num_sets + 1) * sizeof(int));

    for (i = 1; i <= num_sets; ++i)
    {
        int         u = state->pair_vu[i];
        int         v = state->pair_uv[i];

        if (u > 0 && u < i)
            chains[i] = chains[u];
        else if (v > 0 && v < i)
            chains[i] = chains[v];
        else
            chains[i] = ++num_chains;
    }

    /* build result lists. */
    results = palloc0((num_chains + 1) * sizeof(List *));

    for (i = 1; i <= num_sets; ++i)
    {
        int         c = chains[i];

        Assert(c > 0);

        results[c] = list_concat(results[c], orig_sets[i]);
    }

    /* push any empty sets back on the first list. */
    while (num_empty-- > 0)
        results[1] = lcons(NIL, results[1]);

    /* make result list */
    for (i = 1; i <= num_chains; ++i)
        result = lappend(result, results[i]);

    /*
     * Free all the things.
     *
     * (This is over-fussy for small sets but for large sets we could have
     * tied up a nontrivial amount of memory.)
     */
    BipartiteMatchFree(state);
    pfree(results);
    pfree(chains);
    for (i = 1; i <= num_sets; ++i)
        if (adjacency[i])
            pfree(adjacency[i]);
    pfree(adjacency);
    pfree(adjacency_buf);
    pfree(orig_sets);
    for (i = 1; i <= num_sets; ++i)
        bms_free(set_masks[i]);
    pfree(set_masks);

    return result;
}

/*
 * Reorder the elements of a list of grouping sets such that they have correct
 * prefix relationships. Also inserts the GroupingSetData annotations.
 *
 * The input must be ordered with smallest sets first; the result is returned
 * with largest sets first.  Note that the result shares no list substructure
 * with the input, so it's safe for the caller to modify it later.
 *
 * If we're passed in a sortclause, we follow its order of columns to the
 * extent possible, to minimize the chance that we add unnecessary sorts.
 * (We're trying here to ensure that GROUPING SETS ((a,b,c),(c)) ORDER BY c,b,a
 * gets implemented in one pass.)
 */
static List *
reorder_grouping_sets(List *groupingsets, List *sortclause)
{
    ListCell   *lc;
    List       *previous = NIL;
    List       *result = NIL;

    foreach(lc, groupingsets)
    {
        List       *candidate = (List *) lfirst(lc);
        List       *new_elems = list_difference_int(candidate, previous);
        GroupingSetData *gs = makeNode(GroupingSetData);

        while (list_length(sortclause) > list_length(previous) &&
               list_length(new_elems) > 0)
        {
            SortGroupClause *sc = list_nth(sortclause, list_length(previous));
            int         ref = sc->tleSortGroupRef;

            if (list_member_int(new_elems, ref))
            {
                previous = lappend_int(previous, ref);
                new_elems = list_delete_int(new_elems, ref);
            }
            else
            {
                /* diverged from the sortclause; give up on it */
                sortclause = NIL;
                break;
            }
        }

        previous = list_concat(previous, new_elems);

        gs->set = list_copy(previous);
        result = lcons(gs, result);
    }

    list_free(previous);

    return result;
}

/*
 * Compute query_pathkeys and other pathkeys during plan generation
 */
static void
standard_qp_callback(PlannerInfo *root, void *extra)
{
    Query      *parse = root->parse;
    standard_qp_extra *qp_extra = (standard_qp_extra *) extra;
    List       *tlist = root->processed_tlist;
    List       *activeWindows = qp_extra->activeWindows;

    /*
     * Calculate pathkeys that represent grouping/ordering requirements.  The
     * sortClause is certainly sort-able, but GROUP BY and DISTINCT might not
     * be, in which case we just leave their pathkeys empty.
     */
    if (qp_extra->groupClause &&
        grouping_is_sortable(qp_extra->groupClause))
        root->group_pathkeys =
            make_pathkeys_for_sortclauses(root,
                                          qp_extra->groupClause,
                                          tlist);
    else
        root->group_pathkeys = NIL;

    /* We consider only the first (bottom) window in pathkeys logic */
    if (activeWindows != NIL)
    {
        WindowClause *wc = linitial_node(WindowClause, activeWindows);

        root->window_pathkeys = make_pathkeys_for_window(root,
                                                         wc,
                                                         tlist);
    }
    else
        root->window_pathkeys = NIL;

    if (parse->distinctClause &&
        grouping_is_sortable(parse->distinctClause))
        root->distinct_pathkeys =
            make_pathkeys_for_sortclauses(root,
                                          parse->distinctClause,
                                          tlist);
    else
        root->distinct_pathkeys = NIL;

    root->sort_pathkeys =
        make_pathkeys_for_sortclauses(root,
                                      parse->sortClause,
                                      tlist);

    /*
     * Figure out whether we want a sorted result from query_planner.
     *
     * If we have a sortable GROUP BY clause, then we want a result sorted
     * properly for grouping.  Otherwise, if we have window functions to
     * evaluate, we try to sort for the first window.  Otherwise, if there's a
     * sortable DISTINCT clause that's more rigorous than the ORDER BY clause,
     * we try to produce output that's sufficiently well sorted for the
     * DISTINCT.  Otherwise, if there is an ORDER BY clause, we want to sort
     * by the ORDER BY clause.
     *
     * Note: if we have both ORDER BY and GROUP BY, and ORDER BY is a superset
     * of GROUP BY, it would be tempting to request sort by ORDER BY --- but
     * that might just leave us failing to exploit an available sort order at
     * all.  Needs more thought.  The choice for DISTINCT versus ORDER BY is
     * much easier, since we know that the parser ensured that one is a
     * superset of the other.
     */
    if (root->group_pathkeys)
        root->query_pathkeys = root->group_pathkeys;
    else if (root->window_pathkeys)
        root->query_pathkeys = root->window_pathkeys;
    else if (list_length(root->distinct_pathkeys) >
             list_length(root->sort_pathkeys))
        root->query_pathkeys = root->distinct_pathkeys;
    else if (root->sort_pathkeys)
        root->query_pathkeys = root->sort_pathkeys;
    else
        root->query_pathkeys = NIL;
}

/*
 * Estimate number of groups produced by grouping clauses (1 if not grouping)
 *
 * path_rows: number of output rows from scan/join step
 * gd: grouping sets data including list of grouping sets and their clauses
 * target_list: target list containing group clause references
 *
 * If doing grouping sets, we also annotate the gsets data with the estimates
 * for each set and each individual rollup list, with a view to later
 * determining whether some combination of them could be hashed instead.
 */
static double
get_number_of_groups(PlannerInfo *root,
                     double path_rows,
                     grouping_sets_data *gd,
                     List *target_list)
{
    Query      *parse = root->parse;
    double      dNumGroups;

    if (parse->groupClause)
    {
        List       *groupExprs;

        if (parse->groupingSets)
        {
            /* Add up the estimates for each grouping set */
            ListCell   *lc;
            ListCell   *lc2;

            Assert(gd);         /* keep Coverity happy */

            dNumGroups = 0;

            foreach(lc, gd->rollups)
            {
                RollupData *rollup = lfirst_node(RollupData, lc);
                ListCell   *lc;

                groupExprs = get_sortgrouplist_exprs(rollup->groupClause,
                                                     target_list);

                rollup->numGroups = 0.0;

                forboth(lc, rollup->gsets, lc2, rollup->gsets_data)
                {
                    List       *gset = (List *) lfirst(lc);
                    GroupingSetData *gs = lfirst_node(GroupingSetData, lc2);
                    double      numGroups = estimate_num_groups(root,
                                                                groupExprs,
                                                                path_rows,
                                                                &gset,
                                                                NULL);

                    gs->numGroups = numGroups;
                    rollup->numGroups += numGroups;
                }

                dNumGroups += rollup->numGroups;
            }

            if (gd->hash_sets_idx)
            {
                ListCell   *lc;

                gd->dNumHashGroups = 0;

                groupExprs = get_sortgrouplist_exprs(parse->groupClause,
                                                     target_list);

                forboth(lc, gd->hash_sets_idx, lc2, gd->unsortable_sets)
                {
                    List       *gset = (List *) lfirst(lc);
                    GroupingSetData *gs = lfirst_node(GroupingSetData, lc2);
                    double      numGroups = estimate_num_groups(root,
                                                                groupExprs,
                                                                path_rows,
                                                                &gset,
                                                                NULL);

                    gs->numGroups = numGroups;
                    gd->dNumHashGroups += numGroups;
                }

                dNumGroups += gd->dNumHashGroups;
            }
        }
        else
        {
            /* Plain GROUP BY */
            groupExprs = get_sortgrouplist_exprs(parse->groupClause,
                                                 target_list);

            dNumGroups = estimate_num_groups(root, groupExprs, path_rows,
                                             NULL, NULL);
        }
    }
    else if (parse->groupingSets)
    {
        /* Empty grouping sets ... one result row for each one */
        dNumGroups = list_length(parse->groupingSets);
    }
    else if (parse->hasAggs || root->hasHavingQual)
    {
        /* Plain aggregation, one result row */
        dNumGroups = 1;
    }
    else
    {
        /* Not grouping */
        dNumGroups = 1;
    }

    return dNumGroups;
}

/*
 * create_grouping_paths
 *
 * Build a new upperrel containing Paths for grouping and/or aggregation.
 * Along the way, we also build an upperrel for Paths which are partially
 * grouped and/or aggregated.  A partially grouped and/or aggregated path
 * needs a FinalizeAggregate node to complete the aggregation.  Currently,
 * the only partially grouped paths we build are also partial paths; that
 * is, they need a Gather and then a FinalizeAggregate.
 *
 * input_rel: contains the source-data Paths
 * target: the pathtarget for the result Paths to compute
 * gd: grouping sets data including list of grouping sets and their clauses
 *
 * Note: all Paths in input_rel are expected to return the target computed
 * by make_group_input_target.
 */
static RelOptInfo *
create_grouping_paths(PlannerInfo *root,
                      RelOptInfo *input_rel,
                      PathTarget *target,
                      bool target_parallel_safe,
                      grouping_sets_data *gd)
{
    Query      *parse = root->parse;
    RelOptInfo *grouped_rel;
    RelOptInfo *partially_grouped_rel;
    AggClauseCosts agg_costs;

    MemSet(&agg_costs, 0, sizeof(AggClauseCosts));
    get_agg_clause_costs(root, AGGSPLIT_SIMPLE, &agg_costs);

    /*
     * Create grouping relation to hold fully aggregated grouping and/or
     * aggregation paths.
     */
    grouped_rel = make_grouping_rel(root, input_rel, target,
                                    target_parallel_safe, parse->havingQual);

    /*
     * Create either paths for a degenerate grouping or paths for ordinary
     * grouping, as appropriate.
     */
    if (is_degenerate_grouping(root))
        create_degenerate_grouping_paths(root, input_rel, grouped_rel);
    else
    {
        int         flags = 0;
        GroupPathExtraData extra;

        /*
         * Determine whether it's possible to perform sort-based
         * implementations of grouping.  (Note that if groupClause is empty,
         * grouping_is_sortable() is trivially true, and all the
         * pathkeys_contained_in() tests will succeed too, so that we'll
         * consider every surviving input path.)
         *
         * If we have grouping sets, we might be able to sort some but not all
         * of them; in this case, we need can_sort to be true as long as we
         * must consider any sorted-input plan.
         */
        if ((gd && gd->rollups != NIL)
            || grouping_is_sortable(parse->groupClause))
            flags |= GROUPING_CAN_USE_SORT;

        /*
         * Determine whether we should consider hash-based implementations of
         * grouping.
         *
         * Hashed aggregation only applies if we're grouping. If we have
         * grouping sets, some groups might be hashable but others not; in
         * this case we set can_hash true as long as there is nothing globally
         * preventing us from hashing (and we should therefore consider plans
         * with hashes).
         *
         * Executor doesn't support hashed aggregation with DISTINCT or ORDER
         * BY aggregates.  (Doing so would imply storing *all* the input
         * values in the hash table, and/or running many sorts in parallel,
         * either of which seems like a certain loser.)  We similarly don't
         * support ordered-set aggregates in hashed aggregation, but that case
         * is also included in the numOrderedAggs count.
         *
         * Note: grouping_is_hashable() is much more expensive to check than
         * the other gating conditions, so we want to do it last.
         */
        if ((parse->groupClause != NIL &&
             root->numOrderedAggs == 0 &&
             (gd ? gd->any_hashable : grouping_is_hashable(parse->groupClause))))
            flags |= GROUPING_CAN_USE_HASH;

        /*
         * Determine whether partial aggregation is possible.
         */
        if (can_partial_agg(root))
            flags |= GROUPING_CAN_PARTIAL_AGG;

        extra.flags = flags;
        extra.target_parallel_safe = target_parallel_safe;
        extra.havingQual = parse->havingQual;
        extra.targetList = parse->targetList;
        extra.partial_costs_set = false;

        /*
         * Determine whether partitionwise aggregation is in theory possible.
         * It can be disabled by the user, and for now, we don't try to
         * support grouping sets.  create_ordinary_grouping_paths() will check
         * additional conditions, such as whether input_rel is partitioned.
         */
        if (enable_partitionwise_aggregate && !parse->groupingSets)
            extra.patype = PARTITIONWISE_AGGREGATE_FULL;
        else
            extra.patype = PARTITIONWISE_AGGREGATE_NONE;

        create_ordinary_grouping_paths(root, input_rel, grouped_rel,
                                       &agg_costs, gd, &extra,
                                       &partially_grouped_rel);
    }

    set_cheapest(grouped_rel);
    return grouped_rel;
}

/*
 * make_grouping_rel
 *
 * Create a new grouping rel and set basic properties.
 *
 * input_rel represents the underlying scan/join relation.
 * target is the output expected from the grouping relation.
 */
static RelOptInfo *
make_grouping_rel(PlannerInfo *root, RelOptInfo *input_rel,
                  PathTarget *target, bool target_parallel_safe,
                  Node *havingQual)
{
    RelOptInfo *grouped_rel;

    if (IS_OTHER_REL(input_rel))
    {
        grouped_rel = fetch_upper_rel(root, UPPERREL_GROUP_AGG,
                                      input_rel->relids);
        grouped_rel->reloptkind = RELOPT_OTHER_UPPER_REL;
    }
    else
    {
        /*
         * By tradition, the relids set for the main grouping relation is
         * NULL.  (This could be changed, but might require adjustments
         * elsewhere.)
         */
        grouped_rel = fetch_upper_rel(root, UPPERREL_GROUP_AGG, NULL);
    }

    /* Set target. */
    grouped_rel->reltarget = target;

    /*
     * If the input relation is not parallel-safe, then the grouped relation
     * can't be parallel-safe, either.  Otherwise, it's parallel-safe if the
     * target list and HAVING quals are parallel-safe.
     */
    if (input_rel->consider_parallel && target_parallel_safe &&
        is_parallel_safe(root, (Node *) havingQual))
        grouped_rel->consider_parallel = true;

    /*
     * If the input rel belongs to a single FDW, so does the grouped rel.
     */
    grouped_rel->serverid = input_rel->serverid;
    grouped_rel->userid = input_rel->userid;
    grouped_rel->useridiscurrent = input_rel->useridiscurrent;
    grouped_rel->fdwroutine = input_rel->fdwroutine;

    return grouped_rel;
}

/*
 * is_degenerate_grouping
 *
 * A degenerate grouping is one in which the query has a HAVING qual and/or
 * grouping sets, but no aggregates and no GROUP BY (which implies that the
 * grouping sets are all empty).
 */
static bool
is_degenerate_grouping(PlannerInfo *root)
{
    Query      *parse = root->parse;

    return (root->hasHavingQual || parse->groupingSets) &&
        !parse->hasAggs && parse->groupClause == NIL;
}

/*
 * create_degenerate_grouping_paths
 *
 * When the grouping is degenerate (see is_degenerate_grouping), we are
 * supposed to emit either zero or one row for each grouping set depending on
 * whether HAVING succeeds.  Furthermore, there cannot be any variables in
 * either HAVING or the targetlist, so we actually do not need the FROM table
 * at all! We can just throw away the plan-so-far and generate a Result node.
 * This is a sufficiently unusual corner case that it's not worth contorting
 * the structure of this module to avoid having to generate the earlier paths
 * in the first place.
 */
static void
create_degenerate_grouping_paths(PlannerInfo *root, RelOptInfo *input_rel,
                                 RelOptInfo *grouped_rel)
{
    Query      *parse = root->parse;
    int         nrows;
    Path       *path;

    nrows = list_length(parse->groupingSets);
    if (nrows > 1)
    {
        /*
         * Doesn't seem worthwhile writing code to cons up a generate_series
         * or a values scan to emit multiple rows. Instead just make N clones
         * and append them.  (With a volatile HAVING clause, this means you
         * might get between 0 and N output rows. Offhand I think that's
         * desired.)
         */
        List       *paths = NIL;

        while (--nrows >= 0)
        {
            path = (Path *)
                create_group_result_path(root, grouped_rel,
                                         grouped_rel->reltarget,
                                         (List *) parse->havingQual);
            paths = lappend(paths, path);
        }
        path = (Path *)
            create_append_path(root,
                               grouped_rel,
                               paths,
                               NIL,
                               NIL,
                               NULL,
                               0,
                               false,
                               -1);
    }
    else
    {
        /* No grouping sets, or just one, so one output row */
        path = (Path *)
            create_group_result_path(root, grouped_rel,
                                     grouped_rel->reltarget,
                                     (List *) parse->havingQual);
    }

    add_path(grouped_rel, path);
}

/*
 * create_ordinary_grouping_paths
 *
 * Create grouping paths for the ordinary (that is, non-degenerate) case.
 *
 * We need to consider sorted and hashed aggregation in the same function,
 * because otherwise (1) it would be harder to throw an appropriate error
 * message if neither way works, and (2) we should not allow hashtable size
 * considerations to dissuade us from using hashing if sorting is not possible.
 *
 * *partially_grouped_rel_p will be set to the partially grouped rel which this
 * function creates, or to NULL if it doesn't create one.
 */
static void
create_ordinary_grouping_paths(PlannerInfo *root, RelOptInfo *input_rel,
                               RelOptInfo *grouped_rel,
                               const AggClauseCosts *agg_costs,
                               grouping_sets_data *gd,
                               GroupPathExtraData *extra,
                               RelOptInfo **partially_grouped_rel_p)
{
    Path       *cheapest_path = input_rel->cheapest_total_path;
    RelOptInfo *partially_grouped_rel = NULL;
    double      dNumGroups;
    PartitionwiseAggregateType patype = PARTITIONWISE_AGGREGATE_NONE;

    /*
     * If this is the topmost grouping relation or if the parent relation is
     * doing some form of partitionwise aggregation, then we may be able to do
     * it at this level also.  However, if the input relation is not
     * partitioned, partitionwise aggregate is impossible.
     */
    if (extra->patype != PARTITIONWISE_AGGREGATE_NONE &&
        IS_PARTITIONED_REL(input_rel))
    {
        /*
         * If this is the topmost relation or if the parent relation is doing
         * full partitionwise aggregation, then we can do full partitionwise
         * aggregation provided that the GROUP BY clause contains all of the
         * partitioning columns at this level.  Otherwise, we can do at most
         * partial partitionwise aggregation.  But if partial aggregation is
         * not supported in general then we can't use it for partitionwise
         * aggregation either.
         */
        if (extra->patype == PARTITIONWISE_AGGREGATE_FULL &&
            group_by_has_partkey(input_rel, extra->targetList,
                                 root->parse->groupClause))
            patype = PARTITIONWISE_AGGREGATE_FULL;
        else if ((extra->flags & GROUPING_CAN_PARTIAL_AGG) != 0)
            patype = PARTITIONWISE_AGGREGATE_PARTIAL;
        else
            patype = PARTITIONWISE_AGGREGATE_NONE;
    }

    /*
     * Before generating paths for grouped_rel, we first generate any possible
     * partially grouped paths; that way, later code can easily consider both
     * parallel and non-parallel approaches to grouping.
     */
    if ((extra->flags & GROUPING_CAN_PARTIAL_AGG) != 0)
    {
        bool        force_rel_creation;

        /*
         * If we're doing partitionwise aggregation at this level, force
         * creation of a partially_grouped_rel so we can add partitionwise
         * paths to it.
         */
        force_rel_creation = (patype == PARTITIONWISE_AGGREGATE_PARTIAL);

        partially_grouped_rel =
            create_partial_grouping_paths(root,
                                          grouped_rel,
                                          input_rel,
                                          gd,
                                          extra,
                                          force_rel_creation);
    }

    /* Set out parameter. */
    *partially_grouped_rel_p = partially_grouped_rel;

    /* Apply partitionwise aggregation technique, if possible. */
    if (patype != PARTITIONWISE_AGGREGATE_NONE)
        create_partitionwise_grouping_paths(root, input_rel, grouped_rel,
                                            partially_grouped_rel, agg_costs,
                                            gd, patype, extra);

    /* If we are doing partial aggregation only, return. */
    if (extra->patype == PARTITIONWISE_AGGREGATE_PARTIAL)
    {
        Assert(partially_grouped_rel);

        if (partially_grouped_rel->pathlist)
            set_cheapest(partially_grouped_rel);

        return;
    }

    /* Gather any partially grouped partial paths. */
    if (partially_grouped_rel && partially_grouped_rel->partial_pathlist)
    {
        gather_grouping_paths(root, partially_grouped_rel);
        set_cheapest(partially_grouped_rel);
    }

    /*
     * Estimate number of groups.
     */
    dNumGroups = get_number_of_groups(root,
                                      cheapest_path->rows,
                                      gd,
                                      extra->targetList);

    /* Build final grouping paths */
    add_paths_to_grouping_rel(root, input_rel, grouped_rel,
                              partially_grouped_rel, agg_costs, gd,
                              dNumGroups, extra);

    /* Give a helpful error if we failed to find any implementation */
    if (grouped_rel->pathlist == NIL)
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("could not implement GROUP BY"),
                 errdetail("Some of the datatypes only support hashing, while others only support sorting.")));

    /*
     * If there is an FDW that's responsible for all baserels of the query,
     * let it consider adding ForeignPaths.
     */
    if (grouped_rel->fdwroutine &&
        grouped_rel->fdwroutine->GetForeignUpperPaths)
        grouped_rel->fdwroutine->GetForeignUpperPaths(root, UPPERREL_GROUP_AGG,
                                                      input_rel, grouped_rel,
                                                      extra);

    /* Let extensions possibly add some more paths */
    if (create_upper_paths_hook)
        (*create_upper_paths_hook) (root, UPPERREL_GROUP_AGG,
                                    input_rel, grouped_rel,
                                    extra);
}

/*
 * For a given input path, consider the possible ways of doing grouping sets on
 * it, by combinations of hashing and sorting.  This can be called multiple
 * times, so it's important that it not scribble on input.  No result is
 * returned, but any generated paths are added to grouped_rel.
 */
static void
consider_groupingsets_paths(PlannerInfo *root,
                            RelOptInfo *grouped_rel,
                            Path *path,
                            bool is_sorted,
                            bool can_hash,
                            grouping_sets_data *gd,
                            const AggClauseCosts *agg_costs,
                            double dNumGroups)
{
    Query      *parse = root->parse;
    Size        hash_mem_limit = get_hash_memory_limit();

    /*
     * If we're not being offered sorted input, then only consider plans that
     * can be done entirely by hashing.
     *
     * We can hash everything if it looks like it'll fit in hash_mem. But if
     * the input is actually sorted despite not being advertised as such, we
     * prefer to make use of that in order to use less memory.
     *
     * If none of the grouping sets are sortable, then ignore the hash_mem
     * limit and generate a path anyway, since otherwise we'll just fail.
     */
    if (!is_sorted)
    {
        List       *new_rollups = NIL;
        RollupData *unhashed_rollup = NULL;
        List       *sets_data;
        List       *empty_sets_data = NIL;
        List       *empty_sets = NIL;
        ListCell   *lc;
        ListCell   *l_start = list_head(gd->rollups);
        AggStrategy strat = AGG_HASHED;
        double      hashsize;
        double      exclude_groups = 0.0;

        Assert(can_hash);

        /*
         * If the input is coincidentally sorted usefully (which can happen
         * even if is_sorted is false, since that only means that our caller
         * has set up the sorting for us), then save some hashtable space by
         * making use of that. But we need to watch out for degenerate cases:
         *
         * 1) If there are any empty grouping sets, then group_pathkeys might
         * be NIL if all non-empty grouping sets are unsortable. In this case,
         * there will be a rollup containing only empty groups, and the
         * pathkeys_contained_in test is vacuously true; this is ok.
         *
         * XXX: the above relies on the fact that group_pathkeys is generated
         * from the first rollup. If we add the ability to consider multiple
         * sort orders for grouping input, this assumption might fail.
         *
         * 2) If there are no empty sets and only unsortable sets, then the
         * rollups list will be empty (and thus l_start == NULL), and
         * group_pathkeys will be NIL; we must ensure that the vacuously-true
         * pathkeys_contained_in test doesn't cause us to crash.
         */
        if (l_start != NULL &&
            pathkeys_contained_in(root->group_pathkeys, path->pathkeys))
        {
            unhashed_rollup = lfirst_node(RollupData, l_start);
            exclude_groups = unhashed_rollup->numGroups;
            l_start = lnext(gd->rollups, l_start);
        }

        hashsize = estimate_hashagg_tablesize(root,
                                              path,
                                              agg_costs,
                                              dNumGroups - exclude_groups);

        /*
         * gd->rollups is empty if we have only unsortable columns to work
         * with.  Override hash_mem in that case; otherwise, we'll rely on the
         * sorted-input case to generate usable mixed paths.
         */
        if (hashsize > hash_mem_limit && gd->rollups)
            return;             /* nope, won't fit */

        /*
         * We need to burst the existing rollups list into individual grouping
         * sets and recompute a groupClause for each set.
         */
        sets_data = list_copy(gd->unsortable_sets);

        for_each_cell(lc, gd->rollups, l_start)
        {
            RollupData *rollup = lfirst_node(RollupData, lc);

            /*
             * If we find an unhashable rollup that's not been skipped by the
             * "actually sorted" check above, we can't cope; we'd need sorted
             * input (with a different sort order) but we can't get that here.
             * So bail out; we'll get a valid path from the is_sorted case
             * instead.
             *
             * The mere presence of empty grouping sets doesn't make a rollup
             * unhashable (see preprocess_grouping_sets), we handle those
             * specially below.
             */
            if (!rollup->hashable)
                return;

            sets_data = list_concat(sets_data, rollup->gsets_data);
        }
        foreach(lc, sets_data)
        {
            GroupingSetData *gs = lfirst_node(GroupingSetData, lc);
            List       *gset = gs->set;
            RollupData *rollup;

            if (gset == NIL)
            {
                /* Empty grouping sets can't be hashed. */
                empty_sets_data = lappend(empty_sets_data, gs);
                empty_sets = lappend(empty_sets, NIL);
            }
            else
            {
                rollup = makeNode(RollupData);

                rollup->groupClause = preprocess_groupclause(root, gset);
                rollup->gsets_data = list_make1(gs);
                rollup->gsets = remap_to_groupclause_idx(rollup->groupClause,
                                                         rollup->gsets_data,
                                                         gd->tleref_to_colnum_map);
                rollup->numGroups = gs->numGroups;
                rollup->hashable = true;
                rollup->is_hashed = true;
                new_rollups = lappend(new_rollups, rollup);
            }
        }

        /*
         * If we didn't find anything nonempty to hash, then bail.  We'll
         * generate a path from the is_sorted case.
         */
        if (new_rollups == NIL)
            return;

        /*
         * If there were empty grouping sets they should have been in the
         * first rollup.
         */
        Assert(!unhashed_rollup || !empty_sets);

        if (unhashed_rollup)
        {
            new_rollups = lappend(new_rollups, unhashed_rollup);
            strat = AGG_MIXED;
        }
        else if (empty_sets)
        {
            RollupData *rollup = makeNode(RollupData);

            rollup->groupClause = NIL;
            rollup->gsets_data = empty_sets_data;
            rollup->gsets = empty_sets;
            rollup->numGroups = list_length(empty_sets);
            rollup->hashable = false;
            rollup->is_hashed = false;
            new_rollups = lappend(new_rollups, rollup);
            strat = AGG_MIXED;
        }

        add_path(grouped_rel, (Path *)
                 create_groupingsets_path(root,
                                          grouped_rel,
                                          path,
                                          (List *) parse->havingQual,
                                          strat,
                                          new_rollups,
                                          agg_costs,
                                          dNumGroups));
        return;
    }

    /*
     * If we have sorted input but nothing we can do with it, bail.
     */
    if (list_length(gd->rollups) == 0)
        return;

    /*
     * Given sorted input, we try and make two paths: one sorted and one mixed
     * sort/hash. (We need to try both because hashagg might be disabled, or
     * some columns might not be sortable.)
     *
     * can_hash is passed in as false if some obstacle elsewhere (such as
     * ordered aggs) means that we shouldn't consider hashing at all.
     */
    if (can_hash && gd->any_hashable)
    {
        List       *rollups = NIL;
        List       *hash_sets = list_copy(gd->unsortable_sets);
        double      availspace = hash_mem_limit;
        ListCell   *lc;

        /*
         * Account first for space needed for groups we can't sort at all.
         */
        availspace -= estimate_hashagg_tablesize(root,
                                                 path,
                                                 agg_costs,
                                                 gd->dNumHashGroups);

        if (availspace > 0 && list_length(gd->rollups) > 1)
        {
            double      scale;
            int         num_rollups = list_length(gd->rollups);
            int         k_capacity;
            int        *k_weights = palloc(num_rollups * sizeof(int));
            Bitmapset  *hash_items = NULL;
            int         i;

            /*
             * We treat this as a knapsack problem: the knapsack capacity
             * represents hash_mem, the item weights are the estimated memory
             * usage of the hashtables needed to implement a single rollup,
             * and we really ought to use the cost saving as the item value;
             * however, currently the costs assigned to sort nodes don't
             * reflect the comparison costs well, and so we treat all items as
             * of equal value (each rollup we hash instead saves us one sort).
             *
             * To use the discrete knapsack, we need to scale the values to a
             * reasonably small bounded range.  We choose to allow a 5% error
             * margin; we have no more than 4096 rollups in the worst possible
             * case, which with a 5% error margin will require a bit over 42MB
             * of workspace. (Anyone wanting to plan queries that complex had
             * better have the memory for it.  In more reasonable cases, with
             * no more than a couple of dozen rollups, the memory usage will
             * be negligible.)
             *
             * k_capacity is naturally bounded, but we clamp the values for
             * scale and weight (below) to avoid overflows or underflows (or
             * uselessly trying to use a scale factor less than 1 byte).
             */
            scale = Max(availspace / (20.0 * num_rollups), 1.0);
            k_capacity = (int) floor(availspace / scale);

            /*
             * We leave the first rollup out of consideration since it's the
             * one that matches the input sort order.  We assign indexes "i"
             * to only those entries considered for hashing; the second loop,
             * below, must use the same condition.
             */
            i = 0;
            for_each_from(lc, gd->rollups, 1)
            {
                RollupData *rollup = lfirst_node(RollupData, lc);

                if (rollup->hashable)
                {
                    double      sz = estimate_hashagg_tablesize(root,
                                                                path,
                                                                agg_costs,
                                                                rollup->numGroups);

                    /*
                     * If sz is enormous, but hash_mem (and hence scale) is
                     * small, avoid integer overflow here.
                     */
                    k_weights[i] = (int) Min(floor(sz / scale),
                                             k_capacity + 1.0);
                    ++i;
                }
            }

            /*
             * Apply knapsack algorithm; compute the set of items which
             * maximizes the value stored (in this case the number of sorts
             * saved) while keeping the total size (approximately) within
             * capacity.
             */
            if (i > 0)
                hash_items = DiscreteKnapsack(k_capacity, i, k_weights, NULL);

            if (!bms_is_empty(hash_items))
            {
                rollups = list_make1(linitial(gd->rollups));

                i = 0;
                for_each_from(lc, gd->rollups, 1)
                {
                    RollupData *rollup = lfirst_node(RollupData, lc);

                    if (rollup->hashable)
                    {
                        if (bms_is_member(i, hash_items))
                            hash_sets = list_concat(hash_sets,
                                                    rollup->gsets_data);
                        else
                            rollups = lappend(rollups, rollup);
                        ++i;
                    }
                    else
                        rollups = lappend(rollups, rollup);
                }
            }
        }

        if (!rollups && hash_sets)
            rollups = list_copy(gd->rollups);

        foreach(lc, hash_sets)
        {
            GroupingSetData *gs = lfirst_node(GroupingSetData, lc);
            RollupData *rollup = makeNode(RollupData);

            Assert(gs->set != NIL);

            rollup->groupClause = preprocess_groupclause(root, gs->set);
            rollup->gsets_data = list_make1(gs);
            rollup->gsets = remap_to_groupclause_idx(rollup->groupClause,
                                                     rollup->gsets_data,
                                                     gd->tleref_to_colnum_map);
            rollup->numGroups = gs->numGroups;
            rollup->hashable = true;
            rollup->is_hashed = true;
            rollups = lcons(rollup, rollups);
        }

        if (rollups)
        {
            add_path(grouped_rel, (Path *)
                     create_groupingsets_path(root,
                                              grouped_rel,
                                              path,
                                              (List *) parse->havingQual,
                                              AGG_MIXED,
                                              rollups,
                                              agg_costs,
                                              dNumGroups));
        }
    }

    /*
     * Now try the simple sorted case.
     */
    if (!gd->unsortable_sets)
        add_path(grouped_rel, (Path *)
                 create_groupingsets_path(root,
                                          grouped_rel,
                                          path,
                                          (List *) parse->havingQual,
                                          AGG_SORTED,
                                          gd->rollups,
                                          agg_costs,
                                          dNumGroups));
}

/*
 * create_window_paths
 *
 * Build a new upperrel containing Paths for window-function evaluation.
 *
 * input_rel: contains the source-data Paths
 * input_target: result of make_window_input_target
 * output_target: what the topmost WindowAggPath should return
 * wflists: result of find_window_functions
 * activeWindows: result of select_active_windows
 *
 * Note: all Paths in input_rel are expected to return input_target.
 */
static RelOptInfo *
create_window_paths(PlannerInfo *root,
                    RelOptInfo *input_rel,
                    PathTarget *input_target,
                    PathTarget *output_target,
                    bool output_target_parallel_safe,
                    WindowFuncLists *wflists,
                    List *activeWindows)
{
    RelOptInfo *window_rel;
    ListCell   *lc;

    /* For now, do all work in the (WINDOW, NULL) upperrel */
    window_rel = fetch_upper_rel(root, UPPERREL_WINDOW, NULL);

    /*
     * If the input relation is not parallel-safe, then the window relation
     * can't be parallel-safe, either.  Otherwise, we need to examine the
     * target list and active windows for non-parallel-safe constructs.
     */
    if (input_rel->consider_parallel && output_target_parallel_safe &&
        is_parallel_safe(root, (Node *) activeWindows))
        window_rel->consider_parallel = true;

    /*
     * If the input rel belongs to a single FDW, so does the window rel.
     */
    window_rel->serverid = input_rel->serverid;
    window_rel->userid = input_rel->userid;
    window_rel->useridiscurrent = input_rel->useridiscurrent;
    window_rel->fdwroutine = input_rel->fdwroutine;

    /*
     * Consider computing window functions starting from the existing
     * cheapest-total path (which will likely require a sort) as well as any
     * existing paths that satisfy or partially satisfy root->window_pathkeys.
     */
    foreach(lc, input_rel->pathlist)
    {
        Path       *path = (Path *) lfirst(lc);
        int         presorted_keys;

        if (path == input_rel->cheapest_total_path ||
            pathkeys_count_contained_in(root->window_pathkeys, path->pathkeys,
                                        &presorted_keys) ||
            presorted_keys > 0)
            create_one_window_path(root,
                                   window_rel,
                                   path,
                                   input_target,
                                   output_target,
                                   wflists,
                                   activeWindows);
    }

    /*
     * If there is an FDW that's responsible for all baserels of the query,
     * let it consider adding ForeignPaths.
     */
    if (window_rel->fdwroutine &&
        window_rel->fdwroutine->GetForeignUpperPaths)
        window_rel->fdwroutine->GetForeignUpperPaths(root, UPPERREL_WINDOW,
                                                     input_rel, window_rel,
                                                     NULL);

    /* Let extensions possibly add some more paths */
    if (create_upper_paths_hook)
        (*create_upper_paths_hook) (root, UPPERREL_WINDOW,
                                    input_rel, window_rel, NULL);

    /* Now choose the best path(s) */
    set_cheapest(window_rel);

    return window_rel;
}

/*
 * Stack window-function implementation steps atop the given Path, and
 * add the result to window_rel.
 *
 * window_rel: upperrel to contain result
 * path: input Path to use (must return input_target)
 * input_target: result of make_window_input_target
 * output_target: what the topmost WindowAggPath should return
 * wflists: result of find_window_functions
 * activeWindows: result of select_active_windows
 */
static void
create_one_window_path(PlannerInfo *root,
                       RelOptInfo *window_rel,
                       Path *path,
                       PathTarget *input_target,
                       PathTarget *output_target,
                       WindowFuncLists *wflists,
                       List *activeWindows)
{
    PathTarget *window_target;
    ListCell   *l;

    /*
     * Since each window clause could require a different sort order, we stack
     * up a WindowAgg node for each clause, with sort steps between them as
     * needed.  (We assume that select_active_windows chose a good order for
     * executing the clauses in.)
     *
     * input_target should contain all Vars and Aggs needed for the result.
     * (In some cases we wouldn't need to propagate all of these all the way
     * to the top, since they might only be needed as inputs to WindowFuncs.
     * It's probably not worth trying to optimize that though.)  It must also
     * contain all window partitioning and sorting expressions, to ensure
     * they're computed only once at the bottom of the stack (that's critical
     * for volatile functions).  As we climb up the stack, we'll add outputs
     * for the WindowFuncs computed at each level.
     */
    window_target = input_target;

    foreach(l, activeWindows)
    {
        WindowClause *wc = lfirst_node(WindowClause, l);
        List       *window_pathkeys;
        int         presorted_keys;
        bool        is_sorted;

        window_pathkeys = make_pathkeys_for_window(root,
                                                   wc,
                                                   root->processed_tlist);

        is_sorted = pathkeys_count_contained_in(window_pathkeys,
                                                path->pathkeys,
                                                &presorted_keys);

        /* Sort if necessary */
        if (!is_sorted)
        {
            /*
             * No presorted keys or incremental sort disabled, just perform a
             * complete sort.
             */
            if (presorted_keys == 0 || !enable_incremental_sort)
                path = (Path *) create_sort_path(root, window_rel,
                                                 path,
                                                 window_pathkeys,
                                                 -1.0);
            else
            {
                /*
                 * Since we have presorted keys and incremental sort is
                 * enabled, just use incremental sort.
                 */
                path = (Path *) create_incremental_sort_path(root,
                                                             window_rel,
                                                             path,
                                                             window_pathkeys,
                                                             presorted_keys,
                                                             -1.0);
            }
        }

        if (lnext(activeWindows, l))
        {
            /*
             * Add the current WindowFuncs to the output target for this
             * intermediate WindowAggPath.  We must copy window_target to
             * avoid changing the previous path's target.
             *
             * Note: a WindowFunc adds nothing to the target's eval costs; but
             * we do need to account for the increase in tlist width.
             */
            ListCell   *lc2;

            window_target = copy_pathtarget(window_target);
            foreach(lc2, wflists->windowFuncs[wc->winref])
            {
                WindowFunc *wfunc = lfirst_node(WindowFunc, lc2);

                add_column_to_pathtarget(window_target, (Expr *) wfunc, 0);
                window_target->width += get_typavgwidth(wfunc->wintype, -1);
            }
        }
        else
        {
            /* Install the goal target in the topmost WindowAgg */
            window_target = output_target;
        }

        path = (Path *)
            create_windowagg_path(root, window_rel, path, window_target,
                                  wflists->windowFuncs[wc->winref],
                                  wc);
    }

    add_path(window_rel, path);
}

/*
 * create_distinct_paths
 *
 * Build a new upperrel containing Paths for SELECT DISTINCT evaluation.
 *
 * input_rel: contains the source-data Paths
 *
 * Note: input paths should already compute the desired pathtarget, since
 * Sort/Unique won't project anything.
 */
static RelOptInfo *
create_distinct_paths(PlannerInfo *root, RelOptInfo *input_rel)
{
    RelOptInfo *distinct_rel;

    /* For now, do all work in the (DISTINCT, NULL) upperrel */
    distinct_rel = fetch_upper_rel(root, UPPERREL_DISTINCT, NULL);

    /*
     * We don't compute anything at this level, so distinct_rel will be
     * parallel-safe if the input rel is parallel-safe.  In particular, if
     * there is a DISTINCT ON (...) clause, any path for the input_rel will
     * output those expressions, and will not be parallel-safe unless those
     * expressions are parallel-safe.
     */
    distinct_rel->consider_parallel = input_rel->consider_parallel;

    /*
     * If the input rel belongs to a single FDW, so does the distinct_rel.
     */
    distinct_rel->serverid = input_rel->serverid;
    distinct_rel->userid = input_rel->userid;
    distinct_rel->useridiscurrent = input_rel->useridiscurrent;
    distinct_rel->fdwroutine = input_rel->fdwroutine;

    /* build distinct paths based on input_rel's pathlist */
    create_final_distinct_paths(root, input_rel, distinct_rel);

    /* now build distinct paths based on input_rel's partial_pathlist */
    create_partial_distinct_paths(root, input_rel, distinct_rel);

    /* Give a helpful error if we failed to create any paths */
    if (distinct_rel->pathlist == NIL)
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("could not implement DISTINCT"),
                 errdetail("Some of the datatypes only support hashing, while others only support sorting.")));

    /*
     * If there is an FDW that's responsible for all baserels of the query,
     * let it consider adding ForeignPaths.
     */
    if (distinct_rel->fdwroutine &&
        distinct_rel->fdwroutine->GetForeignUpperPaths)
        distinct_rel->fdwroutine->GetForeignUpperPaths(root,
                                                       UPPERREL_DISTINCT,
                                                       input_rel,
                                                       distinct_rel,
                                                       NULL);

    /* Let extensions possibly add some more paths */
    if (create_upper_paths_hook)
        (*create_upper_paths_hook) (root, UPPERREL_DISTINCT, input_rel,
                                    distinct_rel, NULL);

    /* Now choose the best path(s) */
    set_cheapest(distinct_rel);

    return distinct_rel;
}

/*
 * create_partial_distinct_paths
 *
 * Process 'input_rel' partial paths and add unique/aggregate paths to the
 * UPPERREL_PARTIAL_DISTINCT rel.  For paths created, add Gather/GatherMerge
 * paths on top and add a final unique/aggregate path to remove any duplicate
 * produced from combining rows from parallel workers.
 */
static void
create_partial_distinct_paths(PlannerInfo *root, RelOptInfo *input_rel,
                              RelOptInfo *final_distinct_rel)
{
    RelOptInfo *partial_distinct_rel;
    Query      *parse;
    List       *distinctExprs;
    double      numDistinctRows;
    Path       *cheapest_partial_path;
    ListCell   *lc;

    /* nothing to do when there are no partial paths in the input rel */
    if (!input_rel->consider_parallel || input_rel->partial_pathlist == NIL)
        return;

    parse = root->parse;

    /* can't do parallel DISTINCT ON */
    if (parse->hasDistinctOn)
        return;

    partial_distinct_rel = fetch_upper_rel(root, UPPERREL_PARTIAL_DISTINCT,
                                           NULL);
    partial_distinct_rel->reltarget = root->upper_targets[UPPERREL_PARTIAL_DISTINCT];
    partial_distinct_rel->consider_parallel = input_rel->consider_parallel;

    /*
     * If input_rel belongs to a single FDW, so does the partial_distinct_rel.
     */
    partial_distinct_rel->serverid = input_rel->serverid;
    partial_distinct_rel->userid = input_rel->userid;
    partial_distinct_rel->useridiscurrent = input_rel->useridiscurrent;
    partial_distinct_rel->fdwroutine = input_rel->fdwroutine;

    cheapest_partial_path = linitial(input_rel->partial_pathlist);

    distinctExprs = get_sortgrouplist_exprs(parse->distinctClause,
                                            parse->targetList);

    /* estimate how many distinct rows we'll get from each worker */
    numDistinctRows = estimate_num_groups(root, distinctExprs,
                                          cheapest_partial_path->rows,
                                          NULL, NULL);

    /* first try adding unique paths atop of sorted paths */
    if (grouping_is_sortable(parse->distinctClause))
    {
        foreach(lc, input_rel->partial_pathlist)
        {
            Path       *path = (Path *) lfirst(lc);

            if (pathkeys_contained_in(root->distinct_pathkeys, path->pathkeys))
            {
                add_partial_path(partial_distinct_rel, (Path *)
                                 create_upper_unique_path(root,
                                                          partial_distinct_rel,
                                                          path,
                                                          list_length(root->distinct_pathkeys),
                                                          numDistinctRows));
            }
        }
    }

    /*
     * Now try hash aggregate paths, if enabled and hashing is possible. Since
     * we're not on the hook to ensure we do our best to create at least one
     * path here, we treat enable_hashagg as a hard off-switch rather than the
     * slightly softer variant in create_final_distinct_paths.
     */
    if (enable_hashagg && grouping_is_hashable(parse->distinctClause))
    {
        add_partial_path(partial_distinct_rel, (Path *)
                         create_agg_path(root,
                                         partial_distinct_rel,
                                         cheapest_partial_path,
                                         cheapest_partial_path->pathtarget,
                                         AGG_HASHED,
                                         AGGSPLIT_SIMPLE,
                                         parse->distinctClause,
                                         NIL,
                                         NULL,
                                         numDistinctRows));
    }

    /*
     * If there is an FDW that's responsible for all baserels of the query,
     * let it consider adding ForeignPaths.
     */
    if (partial_distinct_rel->fdwroutine &&
        partial_distinct_rel->fdwroutine->GetForeignUpperPaths)
        partial_distinct_rel->fdwroutine->GetForeignUpperPaths(root,
                                                               UPPERREL_PARTIAL_DISTINCT,
                                                               input_rel,
                                                               partial_distinct_rel,
                                                               NULL);

    /* Let extensions possibly add some more partial paths */
    if (create_upper_paths_hook)
        (*create_upper_paths_hook) (root, UPPERREL_PARTIAL_DISTINCT,
                                    input_rel, partial_distinct_rel, NULL);

    if (partial_distinct_rel->partial_pathlist != NIL)
    {
        generate_gather_paths(root, partial_distinct_rel, true);
        set_cheapest(partial_distinct_rel);

        /*
         * Finally, create paths to distinctify the final result.  This step
         * is needed to remove any duplicates due to combining rows from
         * parallel workers.
         */
        create_final_distinct_paths(root, partial_distinct_rel,
                                    final_distinct_rel);
    }
}

/*
 * create_final_distinct_paths
 *      Create distinct paths in 'distinct_rel' based on 'input_rel' pathlist
 *
 * input_rel: contains the source-data paths
 * distinct_rel: destination relation for storing created paths
 */
static RelOptInfo *
create_final_distinct_paths(PlannerInfo *root, RelOptInfo *input_rel,
                            RelOptInfo *distinct_rel)
{
    Query      *parse = root->parse;
    Path       *cheapest_input_path = input_rel->cheapest_total_path;
    double      numDistinctRows;
    bool        allow_hash;
    Path       *path;
    ListCell   *lc;

    /* Estimate number of distinct rows there will be */
    if (parse->groupClause || parse->groupingSets || parse->hasAggs ||
        root->hasHavingQual)
    {
        /*
         * If there was grouping or aggregation, use the number of input rows
         * as the estimated number of DISTINCT rows (ie, assume the input is
         * already mostly unique).
         */
        numDistinctRows = cheapest_input_path->rows;
    }
    else
    {
        /*
         * Otherwise, the UNIQUE filter has effects comparable to GROUP BY.
         */
        List       *distinctExprs;

        distinctExprs = get_sortgrouplist_exprs(parse->distinctClause,
                                                parse->targetList);
        numDistinctRows = estimate_num_groups(root, distinctExprs,
                                              cheapest_input_path->rows,
                                              NULL, NULL);
    }

    /*
     * Consider sort-based implementations of DISTINCT, if possible.
     */
    if (grouping_is_sortable(parse->distinctClause))
    {
        /*
         * First, if we have any adequately-presorted paths, just stick a
         * Unique node on those.  Then consider doing an explicit sort of the
         * cheapest input path and Unique'ing that.
         *
         * When we have DISTINCT ON, we must sort by the more rigorous of
         * DISTINCT and ORDER BY, else it won't have the desired behavior.
         * Also, if we do have to do an explicit sort, we might as well use
         * the more rigorous ordering to avoid a second sort later.  (Note
         * that the parser will have ensured that one clause is a prefix of
         * the other.)
         */
        List       *needed_pathkeys;

        if (parse->hasDistinctOn &&
            list_length(root->distinct_pathkeys) <
            list_length(root->sort_pathkeys))
            needed_pathkeys = root->sort_pathkeys;
        else
            needed_pathkeys = root->distinct_pathkeys;

        foreach(lc, input_rel->pathlist)
        {
            Path       *path = (Path *) lfirst(lc);

            if (pathkeys_contained_in(needed_pathkeys, path->pathkeys))
            {
                add_path(distinct_rel, (Path *)
                         create_upper_unique_path(root, distinct_rel,
                                                  path,
                                                  list_length(root->distinct_pathkeys),
                                                  numDistinctRows));
            }
        }

        /* For explicit-sort case, always use the more rigorous clause */
        if (list_length(root->distinct_pathkeys) <
            list_length(root->sort_pathkeys))
        {
            needed_pathkeys = root->sort_pathkeys;
            /* Assert checks that parser didn't mess up... */
            Assert(pathkeys_contained_in(root->distinct_pathkeys,
                                         needed_pathkeys));
        }
        else
            needed_pathkeys = root->distinct_pathkeys;

        path = cheapest_input_path;
        if (!pathkeys_contained_in(needed_pathkeys, path->pathkeys))
            path = (Path *) create_sort_path(root, distinct_rel,
                                             path,
                                             needed_pathkeys,
                                             -1.0);

        add_path(distinct_rel, (Path *)
                 create_upper_unique_path(root, distinct_rel,
                                          path,
                                          list_length(root->distinct_pathkeys),
                                          numDistinctRows));
    }

    /*
     * Consider hash-based implementations of DISTINCT, if possible.
     *
     * If we were not able to make any other types of path, we *must* hash or
     * die trying.  If we do have other choices, there are two things that
     * should prevent selection of hashing: if the query uses DISTINCT ON
     * (because it won't really have the expected behavior if we hash), or if
     * enable_hashagg is off.
     *
     * Note: grouping_is_hashable() is much more expensive to check than the
     * other gating conditions, so we want to do it last.
     */
    if (distinct_rel->pathlist == NIL)
        allow_hash = true;      /* we have no alternatives */
    else if (parse->hasDistinctOn || !enable_hashagg)
        allow_hash = false;     /* policy-based decision not to hash */
    else
        allow_hash = true;      /* default */

    if (allow_hash && grouping_is_hashable(parse->distinctClause))
    {
        /* Generate hashed aggregate path --- no sort needed */
        add_path(distinct_rel, (Path *)
                 create_agg_path(root,
                                 distinct_rel,
                                 cheapest_input_path,
                                 cheapest_input_path->pathtarget,
                                 AGG_HASHED,
                                 AGGSPLIT_SIMPLE,
                                 parse->distinctClause,
                                 NIL,
                                 NULL,
                                 numDistinctRows));
    }

    return distinct_rel;
}

/*
 * create_ordered_paths
 *
 * Build a new upperrel containing Paths for ORDER BY evaluation.
 *
 * All paths in the result must satisfy the ORDER BY ordering.
 * The only new paths we need consider are an explicit full sort
 * and incremental sort on the cheapest-total existing path.
 *
 * input_rel: contains the source-data Paths
 * target: the output tlist the result Paths must emit
 * limit_tuples: estimated bound on the number of output tuples,
 *      or -1 if no LIMIT or couldn't estimate
 *
 * XXX This only looks at sort_pathkeys. I wonder if it needs to look at the
 * other pathkeys (grouping, ...) like generate_useful_gather_paths.
 */
static RelOptInfo *
create_ordered_paths(PlannerInfo *root,
                     RelOptInfo *input_rel,
                     PathTarget *target,
                     bool target_parallel_safe,
                     double limit_tuples)
{
    Path       *cheapest_input_path = input_rel->cheapest_total_path;
    RelOptInfo *ordered_rel;
    ListCell   *lc;

    /* For now, do all work in the (ORDERED, NULL) upperrel */
    ordered_rel = fetch_upper_rel(root, UPPERREL_ORDERED, NULL);

    /*
     * If the input relation is not parallel-safe, then the ordered relation
     * can't be parallel-safe, either.  Otherwise, it's parallel-safe if the
     * target list is parallel-safe.
     */
    if (input_rel->consider_parallel && target_parallel_safe)
        ordered_rel->consider_parallel = true;

    /*
     * If the input rel belongs to a single FDW, so does the ordered_rel.
     */
    ordered_rel->serverid = input_rel->serverid;
    ordered_rel->userid = input_rel->userid;
    ordered_rel->useridiscurrent = input_rel->useridiscurrent;
    ordered_rel->fdwroutine = input_rel->fdwroutine;

    foreach(lc, input_rel->pathlist)
    {
        Path       *input_path = (Path *) lfirst(lc);
        Path       *sorted_path = input_path;
        bool        is_sorted;
        int         presorted_keys;

        is_sorted = pathkeys_count_contained_in(root->sort_pathkeys,
                                                input_path->pathkeys, &presorted_keys);

        if (is_sorted)
        {
            /* Use the input path as is, but add a projection step if needed */
            if (sorted_path->pathtarget != target)
                sorted_path = apply_projection_to_path(root, ordered_rel,
                                                       sorted_path, target);

            add_path(ordered_rel, sorted_path);
        }
        else
        {
            /*
             * Try adding an explicit sort, but only to the cheapest total
             * path since a full sort should generally add the same cost to
             * all paths.
             */
            if (input_path == cheapest_input_path)
            {
                /*
                 * Sort the cheapest input path. An explicit sort here can
                 * take advantage of LIMIT.
                 */
                sorted_path = (Path *) create_sort_path(root,
                                                        ordered_rel,
                                                        input_path,
                                                        root->sort_pathkeys,
                                                        limit_tuples);
                /* Add projection step if needed */
                if (sorted_path->pathtarget != target)
                    sorted_path = apply_projection_to_path(root, ordered_rel,
                                                           sorted_path, target);

                add_path(ordered_rel, sorted_path);
            }

            /*
             * If incremental sort is enabled, then try it as well. Unlike
             * with regular sorts, we can't just look at the cheapest path,
             * because the cost of incremental sort depends on how well
             * presorted the path is. Additionally incremental sort may enable
             * a cheaper startup path to win out despite higher total cost.
             */
            if (!enable_incremental_sort)
                continue;

            /* Likewise, if the path can't be used for incremental sort. */
            if (!presorted_keys)
                continue;

            /* Also consider incremental sort. */
            sorted_path = (Path *) create_incremental_sort_path(root,
                                                                ordered_rel,
                                                                input_path,
                                                                root->sort_pathkeys,
                                                                presorted_keys,
                                                                limit_tuples);

            /* Add projection step if needed */
            if (sorted_path->pathtarget != target)
                sorted_path = apply_projection_to_path(root, ordered_rel,
                                                       sorted_path, target);

            add_path(ordered_rel, sorted_path);
        }
    }

    /*
     * generate_gather_paths() will have already generated a simple Gather
     * path for the best parallel path, if any, and the loop above will have
     * considered sorting it.  Similarly, generate_gather_paths() will also
     * have generated order-preserving Gather Merge plans which can be used
     * without sorting if they happen to match the sort_pathkeys, and the loop
     * above will have handled those as well.  However, there's one more
     * possibility: it may make sense to sort the cheapest partial path
     * according to the required output order and then use Gather Merge.
     */
    if (ordered_rel->consider_parallel && root->sort_pathkeys != NIL &&
        input_rel->partial_pathlist != NIL)
    {
        Path       *cheapest_partial_path;

        cheapest_partial_path = linitial(input_rel->partial_pathlist);

        /*
         * If cheapest partial path doesn't need a sort, this is redundant
         * with what's already been tried.
         */
        if (!pathkeys_contained_in(root->sort_pathkeys,
                                   cheapest_partial_path->pathkeys))
        {
            Path       *path;
            double      total_groups;

            path = (Path *) create_sort_path(root,
                                             ordered_rel,
                                             cheapest_partial_path,
                                             root->sort_pathkeys,
                                             limit_tuples);

            total_groups = cheapest_partial_path->rows *
                cheapest_partial_path->parallel_workers;
            path = (Path *)
                create_gather_merge_path(root, ordered_rel,
                                         path,
                                         path->pathtarget,
                                         root->sort_pathkeys, NULL,
                                         &total_groups);

            /* Add projection step if needed */
            if (path->pathtarget != target)
                path = apply_projection_to_path(root, ordered_rel,
                                                path, target);

            add_path(ordered_rel, path);
        }

        /*
         * Consider incremental sort with a gather merge on partial paths.
         *
         * We can also skip the entire loop when we only have a single-item
         * sort_pathkeys because then we can't possibly have a presorted
         * prefix of the list without having the list be fully sorted.
         */
        if (enable_incremental_sort && list_length(root->sort_pathkeys) > 1)
        {
            ListCell   *lc;

            foreach(lc, input_rel->partial_pathlist)
            {
                Path       *input_path = (Path *) lfirst(lc);
                Path       *sorted_path;
                bool        is_sorted;
                int         presorted_keys;
                double      total_groups;

                /*
                 * We don't care if this is the cheapest partial path - we
                 * can't simply skip it, because it may be partially sorted in
                 * which case we want to consider adding incremental sort
                 * (instead of full sort, which is what happens above).
                 */

                is_sorted = pathkeys_count_contained_in(root->sort_pathkeys,
                                                        input_path->pathkeys,
                                                        &presorted_keys);

                /* No point in adding incremental sort on fully sorted paths. */
                if (is_sorted)
                    continue;

                if (presorted_keys == 0)
                    continue;

                /* Since we have presorted keys, consider incremental sort. */
                sorted_path = (Path *) create_incremental_sort_path(root,
                                                                    ordered_rel,
                                                                    input_path,
                                                                    root->sort_pathkeys,
                                                                    presorted_keys,
                                                                    limit_tuples);
                total_groups = input_path->rows *
                    input_path->parallel_workers;
                sorted_path = (Path *)
                    create_gather_merge_path(root, ordered_rel,
                                             sorted_path,
                                             sorted_path->pathtarget,
                                             root->sort_pathkeys, NULL,
                                             &total_groups);

                /* Add projection step if needed */
                if (sorted_path->pathtarget != target)
                    sorted_path = apply_projection_to_path(root, ordered_rel,
                                                           sorted_path, target);

                add_path(ordered_rel, sorted_path);
            }
        }
    }

    /*
     * If there is an FDW that's responsible for all baserels of the query,
     * let it consider adding ForeignPaths.
     */
    if (ordered_rel->fdwroutine &&
        ordered_rel->fdwroutine->GetForeignUpperPaths)
        ordered_rel->fdwroutine->GetForeignUpperPaths(root, UPPERREL_ORDERED,
                                                      input_rel, ordered_rel,
                                                      NULL);

    /* Let extensions possibly add some more paths */
    if (create_upper_paths_hook)
        (*create_upper_paths_hook) (root, UPPERREL_ORDERED,
                                    input_rel, ordered_rel, NULL);

    /*
     * No need to bother with set_cheapest here; grouping_planner does not
     * need us to do it.
     */
    Assert(ordered_rel->pathlist != NIL);

    return ordered_rel;
}


/*
 * make_group_input_target
 *    Generate appropriate PathTarget for initial input to grouping nodes.
 *
 * If there is grouping or aggregation, the scan/join subplan cannot emit
 * the query's final targetlist; for example, it certainly can't emit any
 * aggregate function calls.  This routine generates the correct target
 * for the scan/join subplan.
 *
 * The query target list passed from the parser already contains entries
 * for all ORDER BY and GROUP BY expressions, but it will not have entries
 * for variables used only in HAVING clauses; so we need to add those
 * variables to the subplan target list.  Also, we flatten all expressions
 * except GROUP BY items into their component variables; other expressions
 * will be computed by the upper plan nodes rather than by the subplan.
 * For example, given a query like
 *      SELECT a+b,SUM(c+d) FROM table GROUP BY a+b;
 * we want to pass this targetlist to the subplan:
 *      a+b,c,d
 * where the a+b target will be used by the Sort/Group steps, and the
 * other targets will be used for computing the final results.
 *
 * 'final_target' is the query's final target list (in PathTarget form)
 *
 * The result is the PathTarget to be computed by the Paths returned from
 * query_planner().
 */
static PathTarget *
make_group_input_target(PlannerInfo *root, PathTarget *final_target)
{
    Query      *parse = root->parse;
    PathTarget *input_target;
    List       *non_group_cols;
    List       *non_group_vars;
    int         i;
    ListCell   *lc;

    /*
     * We must build a target containing all grouping columns, plus any other
     * Vars mentioned in the query's targetlist and HAVING qual.
     */
    input_target = create_empty_pathtarget();
    non_group_cols = NIL;

    i = 0;
    foreach(lc, final_target->exprs)
    {
        Expr       *expr = (Expr *) lfirst(lc);
        Index       sgref = get_pathtarget_sortgroupref(final_target, i);

        if (sgref && parse->groupClause &&
            get_sortgroupref_clause_noerr(sgref, parse->groupClause) != NULL)
        {
            /*
             * It's a grouping column, so add it to the input target as-is.
             */
            add_column_to_pathtarget(input_target, expr, sgref);
        }
        else
        {
            /*
             * Non-grouping column, so just remember the expression for later
             * call to pull_var_clause.
             */
            non_group_cols = lappend(non_group_cols, expr);
        }

        i++;
    }

    /*
     * If there's a HAVING clause, we'll need the Vars it uses, too.
     */
    if (parse->havingQual)
        non_group_cols = lappend(non_group_cols, parse->havingQual);

    /*
     * Pull out all the Vars mentioned in non-group cols (plus HAVING), and
     * add them to the input target if not already present.  (A Var used
     * directly as a GROUP BY item will be present already.)  Note this
     * includes Vars used in resjunk items, so we are covering the needs of
     * ORDER BY and window specifications.  Vars used within Aggrefs and
     * WindowFuncs will be pulled out here, too.
     */
    non_group_vars = pull_var_clause((Node *) non_group_cols,
                                     PVC_RECURSE_AGGREGATES |
                                     PVC_RECURSE_WINDOWFUNCS |
                                     PVC_INCLUDE_PLACEHOLDERS);
    add_new_columns_to_pathtarget(input_target, non_group_vars);

    /* clean up cruft */
    list_free(non_group_vars);
    list_free(non_group_cols);

    /* XXX this causes some redundant cost calculation ... */
    return set_pathtarget_cost_width(root, input_target);
}

/*
 * make_partial_grouping_target
 *    Generate appropriate PathTarget for output of partial aggregate
 *    (or partial grouping, if there are no aggregates) nodes.
 *
 * A partial aggregation node needs to emit all the same aggregates that
 * a regular aggregation node would, plus any aggregates used in HAVING;
 * except that the Aggref nodes should be marked as partial aggregates.
 *
 * In addition, we'd better emit any Vars and PlaceHolderVars that are
 * used outside of Aggrefs in the aggregation tlist and HAVING.  (Presumably,
 * these would be Vars that are grouped by or used in grouping expressions.)
 *
 * grouping_target is the tlist to be emitted by the topmost aggregation step.
 * havingQual represents the HAVING clause.
 */
static PathTarget *
make_partial_grouping_target(PlannerInfo *root,
                             PathTarget *grouping_target,
                             Node *havingQual)
{
    Query      *parse = root->parse;
    PathTarget *partial_target;
    List       *non_group_cols;
    List       *non_group_exprs;
    int         i;
    ListCell   *lc;

    partial_target = create_empty_pathtarget();
    non_group_cols = NIL;

    i = 0;
    foreach(lc, grouping_target->exprs)
    {
        Expr       *expr = (Expr *) lfirst(lc);
        Index       sgref = get_pathtarget_sortgroupref(grouping_target, i);

        if (sgref && parse->groupClause &&
            get_sortgroupref_clause_noerr(sgref, parse->groupClause) != NULL)
        {
            /*
             * It's a grouping column, so add it to the partial_target as-is.
             * (This allows the upper agg step to repeat the grouping calcs.)
             */
            add_column_to_pathtarget(partial_target, expr, sgref);
        }
        else
        {
            /*
             * Non-grouping column, so just remember the expression for later
             * call to pull_var_clause.
             */
            non_group_cols = lappend(non_group_cols, expr);
        }

        i++;
    }

    /*
     * If there's a HAVING clause, we'll need the Vars/Aggrefs it uses, too.
     */
    if (havingQual)
        non_group_cols = lappend(non_group_cols, havingQual);

    /*
     * Pull out all the Vars, PlaceHolderVars, and Aggrefs mentioned in
     * non-group cols (plus HAVING), and add them to the partial_target if not
     * already present.  (An expression used directly as a GROUP BY item will
     * be present already.)  Note this includes Vars used in resjunk items, so
     * we are covering the needs of ORDER BY and window specifications.
     */
    non_group_exprs = pull_var_clause((Node *) non_group_cols,
                                      PVC_INCLUDE_AGGREGATES |
                                      PVC_RECURSE_WINDOWFUNCS |
                                      PVC_INCLUDE_PLACEHOLDERS);

    add_new_columns_to_pathtarget(partial_target, non_group_exprs);

    /*
     * Adjust Aggrefs to put them in partial mode.  At this point all Aggrefs
     * are at the top level of the target list, so we can just scan the list
     * rather than recursing through the expression trees.
     */
    foreach(lc, partial_target->exprs)
    {
        Aggref     *aggref = (Aggref *) lfirst(lc);

        if (IsA(aggref, Aggref))
        {
            Aggref     *newaggref;

            /*
             * We shouldn't need to copy the substructure of the Aggref node,
             * but flat-copy the node itself to avoid damaging other trees.
             */
            newaggref = makeNode(Aggref);
            memcpy(newaggref, aggref, sizeof(Aggref));

            /* For now, assume serialization is required */
            mark_partial_aggref(newaggref, AGGSPLIT_INITIAL_SERIAL);

            lfirst(lc) = newaggref;
        }
    }

    /* clean up cruft */
    list_free(non_group_exprs);
    list_free(non_group_cols);

    /* XXX this causes some redundant cost calculation ... */
    return set_pathtarget_cost_width(root, partial_target);
}

/*
 * mark_partial_aggref
 *    Adjust an Aggref to make it represent a partial-aggregation step.
 *
 * The Aggref node is modified in-place; caller must do any copying required.
 */
void
mark_partial_aggref(Aggref *agg, AggSplit aggsplit)
{
    /* aggtranstype should be computed by this point */
    Assert(OidIsValid(agg->aggtranstype));
    /* ... but aggsplit should still be as the parser left it */
    Assert(agg->aggsplit == AGGSPLIT_SIMPLE);

    /* Mark the Aggref with the intended partial-aggregation mode */
    agg->aggsplit = aggsplit;

    /*
     * Adjust result type if needed.  Normally, a partial aggregate returns
     * the aggregate's transition type; but if that's INTERNAL and we're
     * serializing, it returns BYTEA instead.
     */
    if (DO_AGGSPLIT_SKIPFINAL(aggsplit))
    {
        if (agg->aggtranstype == INTERNALOID && DO_AGGSPLIT_SERIALIZE(aggsplit))
            agg->aggtype = BYTEAOID;
        else
            agg->aggtype = agg->aggtranstype;
    }
}

/*
 * postprocess_setop_tlist
 *    Fix up targetlist returned by plan_set_operations().
 *
 * We need to transpose sort key info from the orig_tlist into new_tlist.
 * NOTE: this would not be good enough if we supported resjunk sort keys
 * for results of set operations --- then, we'd need to project a whole
 * new tlist to evaluate the resjunk columns.  For now, just ereport if we
 * find any resjunk columns in orig_tlist.
 */
static List *
postprocess_setop_tlist(List *new_tlist, List *orig_tlist)
{
    ListCell   *l;
    ListCell   *orig_tlist_item = list_head(orig_tlist);

    foreach(l, new_tlist)
    {
        TargetEntry *new_tle = lfirst_node(TargetEntry, l);
        TargetEntry *orig_tle;

        /* ignore resjunk columns in setop result */
        if (new_tle->resjunk)
            continue;

        Assert(orig_tlist_item != NULL);
        orig_tle = lfirst_node(TargetEntry, orig_tlist_item);
        orig_tlist_item = lnext(orig_tlist, orig_tlist_item);
        if (orig_tle->resjunk)  /* should not happen */
            elog(ERROR, "resjunk output columns are not implemented");
        Assert(new_tle->resno == orig_tle->resno);
        new_tle->ressortgroupref = orig_tle->ressortgroupref;
    }
    if (orig_tlist_item != NULL)
        elog(ERROR, "resjunk output columns are not implemented");
    return new_tlist;
}

/*
 * select_active_windows
 *      Create a list of the "active" window clauses (ie, those referenced
 *      by non-deleted WindowFuncs) in the order they are to be executed.
 */
static List *
select_active_windows(PlannerInfo *root, WindowFuncLists *wflists)
{
    List       *windowClause = root->parse->windowClause;
    List       *result = NIL;
    ListCell   *lc;
    int         nActive = 0;
    WindowClauseSortData *actives = palloc(sizeof(WindowClauseSortData)
                                           * list_length(windowClause));

    /* First, construct an array of the active windows */
    foreach(lc, windowClause)
    {
        WindowClause *wc = lfirst_node(WindowClause, lc);

        /* It's only active if wflists shows some related WindowFuncs */
        Assert(wc->winref <= wflists->maxWinRef);
        if (wflists->windowFuncs[wc->winref] == NIL)
            continue;

        actives[nActive].wc = wc;   /* original clause */

        /*
         * For sorting, we want the list of partition keys followed by the
         * list of sort keys. But pathkeys construction will remove duplicates
         * between the two, so we can as well (even though we can't detect all
         * of the duplicates, since some may come from ECs - that might mean
         * we miss optimization chances here). We must, however, ensure that
         * the order of entries is preserved with respect to the ones we do
         * keep.
         *
         * partitionClause and orderClause had their own duplicates removed in
         * parse analysis, so we're only concerned here with removing
         * orderClause entries that also appear in partitionClause.
         */
        actives[nActive].uniqueOrder =
            list_concat_unique(list_copy(wc->partitionClause),
                               wc->orderClause);
        nActive++;
    }

    /*
     * Sort active windows by their partitioning/ordering clauses, ignoring
     * any framing clauses, so that the windows that need the same sorting are
     * adjacent in the list. When we come to generate paths, this will avoid
     * inserting additional Sort nodes.
     *
     * This is how we implement a specific requirement from the SQL standard,
     * which says that when two or more windows are order-equivalent (i.e.
     * have matching partition and order clauses, even if their names or
     * framing clauses differ), then all peer rows must be presented in the
     * same order in all of them. If we allowed multiple sort nodes for such
     * cases, we'd risk having the peer rows end up in different orders in
     * equivalent windows due to sort instability. (See General Rule 4 of
     * <window clause> in SQL2008 - SQL2016.)
     *
     * Additionally, if the entire list of clauses of one window is a prefix
     * of another, put first the window with stronger sorting requirements.
     * This way we will first sort for stronger window, and won't have to sort
     * again for the weaker one.
     */
    qsort(actives, nActive, sizeof(WindowClauseSortData), common_prefix_cmp);

    /* build ordered list of the original WindowClause nodes */
    for (int i = 0; i < nActive; i++)
        result = lappend(result, actives[i].wc);

    pfree(actives);

    return result;
}

/*
 * common_prefix_cmp
 *    QSort comparison function for WindowClauseSortData
 *
 * Sort the windows by the required sorting clauses. First, compare the sort
 * clauses themselves. Second, if one window's clauses are a prefix of another
 * one's clauses, put the window with more sort clauses first.
 */
static int
common_prefix_cmp(const void *a, const void *b)
{
    const WindowClauseSortData *wcsa = a;
    const WindowClauseSortData *wcsb = b;
    ListCell   *item_a;
    ListCell   *item_b;

    forboth(item_a, wcsa->uniqueOrder, item_b, wcsb->uniqueOrder)
    {
        SortGroupClause *sca = lfirst_node(SortGroupClause, item_a);
        SortGroupClause *scb = lfirst_node(SortGroupClause, item_b);

        if (sca->tleSortGroupRef > scb->tleSortGroupRef)
            return -1;
        else if (sca->tleSortGroupRef < scb->tleSortGroupRef)
            return 1;
        else if (sca->sortop > scb->sortop)
            return -1;
        else if (sca->sortop < scb->sortop)
            return 1;
        else if (sca->nulls_first && !scb->nulls_first)
            return -1;
        else if (!sca->nulls_first && scb->nulls_first)
            return 1;
        /* no need to compare eqop, since it is fully determined by sortop */
    }

    if (list_length(wcsa->uniqueOrder) > list_length(wcsb->uniqueOrder))
        return -1;
    else if (list_length(wcsa->uniqueOrder) < list_length(wcsb->uniqueOrder))
        return 1;

    return 0;
}

/*
 * make_window_input_target
 *    Generate appropriate PathTarget for initial input to WindowAgg nodes.
 *
 * When the query has window functions, this function computes the desired
 * target to be computed by the node just below the first WindowAgg.
 * This tlist must contain all values needed to evaluate the window functions,
 * compute the final target list, and perform any required final sort step.
 * If multiple WindowAggs are needed, each intermediate one adds its window
 * function results onto this base tlist; only the topmost WindowAgg computes
 * the actual desired target list.
 *
 * This function is much like make_group_input_target, though not quite enough
 * like it to share code.  As in that function, we flatten most expressions
 * into their component variables.  But we do not want to flatten window
 * PARTITION BY/ORDER BY clauses, since that might result in multiple
 * evaluations of them, which would be bad (possibly even resulting in
 * inconsistent answers, if they contain volatile functions).
 * Also, we must not flatten GROUP BY clauses that were left unflattened by
 * make_group_input_target, because we may no longer have access to the
 * individual Vars in them.
 *
 * Another key difference from make_group_input_target is that we don't
 * flatten Aggref expressions, since those are to be computed below the
 * window functions and just referenced like Vars above that.
 *
 * 'final_target' is the query's final target list (in PathTarget form)
 * 'activeWindows' is the list of active windows previously identified by
 *          select_active_windows.
 *
 * The result is the PathTarget to be computed by the plan node immediately
 * below the first WindowAgg node.
 */
static PathTarget *
make_window_input_target(PlannerInfo *root,
                         PathTarget *final_target,
                         List *activeWindows)
{
    Query      *parse = root->parse;
    PathTarget *input_target;
    Bitmapset  *sgrefs;
    List       *flattenable_cols;
    List       *flattenable_vars;
    int         i;
    ListCell   *lc;

    Assert(parse->hasWindowFuncs);

    /*
     * Collect the sortgroupref numbers of window PARTITION/ORDER BY clauses
     * into a bitmapset for convenient reference below.
     */
    sgrefs = NULL;
    foreach(lc, activeWindows)
    {
        WindowClause *wc = lfirst_node(WindowClause, lc);
        ListCell   *lc2;

        foreach(lc2, wc->partitionClause)
        {
            SortGroupClause *sortcl = lfirst_node(SortGroupClause, lc2);

            sgrefs = bms_add_member(sgrefs, sortcl->tleSortGroupRef);
        }
        foreach(lc2, wc->orderClause)
        {
            SortGroupClause *sortcl = lfirst_node(SortGroupClause, lc2);

            sgrefs = bms_add_member(sgrefs, sortcl->tleSortGroupRef);
        }
    }

    /* Add in sortgroupref numbers of GROUP BY clauses, too */
    foreach(lc, parse->groupClause)
    {
        SortGroupClause *grpcl = lfirst_node(SortGroupClause, lc);

        sgrefs = bms_add_member(sgrefs, grpcl->tleSortGroupRef);
    }

    /*
     * Construct a target containing all the non-flattenable targetlist items,
     * and save aside the others for a moment.
     */
    input_target = create_empty_pathtarget();
    flattenable_cols = NIL;

    i = 0;
    foreach(lc, final_target->exprs)
    {
        Expr       *expr = (Expr *) lfirst(lc);
        Index       sgref = get_pathtarget_sortgroupref(final_target, i);

        /*
         * Don't want to deconstruct window clauses or GROUP BY items.  (Note
         * that such items can't contain window functions, so it's okay to
         * compute them below the WindowAgg nodes.)
         */
        if (sgref != 0 && bms_is_member(sgref, sgrefs))
        {
            /*
             * Don't want to deconstruct this value, so add it to the input
             * target as-is.
             */
            add_column_to_pathtarget(input_target, expr, sgref);
        }
        else
        {
            /*
             * Column is to be flattened, so just remember the expression for
             * later call to pull_var_clause.
             */
            flattenable_cols = lappend(flattenable_cols, expr);
        }

        i++;
    }

    /*
     * Pull out all the Vars and Aggrefs mentioned in flattenable columns, and
     * add them to the input target if not already present.  (Some might be
     * there already because they're used directly as window/group clauses.)
     *
     * Note: it's essential to use PVC_INCLUDE_AGGREGATES here, so that any
     * Aggrefs are placed in the Agg node's tlist and not left to be computed
     * at higher levels.  On the other hand, we should recurse into
     * WindowFuncs to make sure their input expressions are available.
     */
    flattenable_vars = pull_var_clause((Node *) flattenable_cols,
                                       PVC_INCLUDE_AGGREGATES |
                                       PVC_RECURSE_WINDOWFUNCS |
                                       PVC_INCLUDE_PLACEHOLDERS);
    add_new_columns_to_pathtarget(input_target, flattenable_vars);

    /* clean up cruft */
    list_free(flattenable_vars);
    list_free(flattenable_cols);

    /* XXX this causes some redundant cost calculation ... */
    return set_pathtarget_cost_width(root, input_target);
}

/*
 * make_pathkeys_for_window
 *      Create a pathkeys list describing the required input ordering
 *      for the given WindowClause.
 *
 * The required ordering is first the PARTITION keys, then the ORDER keys.
 * In the future we might try to implement windowing using hashing, in which
 * case the ordering could be relaxed, but for now we always sort.
 */
static List *
make_pathkeys_for_window(PlannerInfo *root, WindowClause *wc,
                         List *tlist)
{
    List       *window_pathkeys;
    List       *window_sortclauses;

    /* Throw error if can't sort */
    if (!grouping_is_sortable(wc->partitionClause))
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("could not implement window PARTITION BY"),
                 errdetail("Window partitioning columns must be of sortable datatypes.")));
    if (!grouping_is_sortable(wc->orderClause))
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("could not implement window ORDER BY"),
                 errdetail("Window ordering columns must be of sortable datatypes.")));

    /* Okay, make the combined pathkeys */
    window_sortclauses = list_concat_copy(wc->partitionClause, wc->orderClause);
    window_pathkeys = make_pathkeys_for_sortclauses(root,
                                                    window_sortclauses,
                                                    tlist);
    list_free(window_sortclauses);
    return window_pathkeys;
}

/*
 * make_sort_input_target
 *    Generate appropriate PathTarget for initial input to Sort step.
 *
 * If the query has ORDER BY, this function chooses the target to be computed
 * by the node just below the Sort (and DISTINCT, if any, since Unique can't
 * project) steps.  This might or might not be identical to the query's final
 * output target.
 *
 * The main argument for keeping the sort-input tlist the same as the final
 * is that we avoid a separate projection node (which will be needed if
 * they're different, because Sort can't project).  However, there are also
 * advantages to postponing tlist evaluation till after the Sort: it ensures
 * a consistent order of evaluation for any volatile functions in the tlist,
 * and if there's also a LIMIT, we can stop the query without ever computing
 * tlist functions for later rows, which is beneficial for both volatile and
 * expensive functions.
 *
 * Our current policy is to postpone volatile expressions till after the sort
 * unconditionally (assuming that that's possible, ie they are in plain tlist
 * columns and not ORDER BY/GROUP BY/DISTINCT columns).  We also prefer to
 * postpone set-returning expressions, because running them beforehand would
 * bloat the sort dataset, and because it might cause unexpected output order
 * if the sort isn't stable.  However there's a constraint on that: all SRFs
 * in the tlist should be evaluated at the same plan step, so that they can
 * run in sync in nodeProjectSet.  So if any SRFs are in sort columns, we
 * mustn't postpone any SRFs.  (Note that in principle that policy should
 * probably get applied to the group/window input targetlists too, but we
 * have not done that historically.)  Lastly, expensive expressions are
 * postponed if there is a LIMIT, or if root->tuple_fraction shows that
 * partial evaluation of the query is possible (if neither is true, we expect
 * to have to evaluate the expressions for every row anyway), or if there are
 * any volatile or set-returning expressions (since once we've put in a
 * projection at all, it won't cost any more to postpone more stuff).
 *
 * Another issue that could potentially be considered here is that
 * evaluating tlist expressions could result in data that's either wider
 * or narrower than the input Vars, thus changing the volume of data that
 * has to go through the Sort.  However, we usually have only a very bad
 * idea of the output width of any expression more complex than a Var,
 * so for now it seems too risky to try to optimize on that basis.
 *
 * Note that if we do produce a modified sort-input target, and then the
 * query ends up not using an explicit Sort, no particular harm is done:
 * we'll initially use the modified target for the preceding path nodes,
 * but then change them to the final target with apply_projection_to_path.
 * Moreover, in such a case the guarantees about evaluation order of
 * volatile functions still hold, since the rows are sorted already.
 *
 * This function has some things in common with make_group_input_target and
 * make_window_input_target, though the detailed rules for what to do are
 * different.  We never flatten/postpone any grouping or ordering columns;
 * those are needed before the sort.  If we do flatten a particular
 * expression, we leave Aggref and WindowFunc nodes alone, since those were
 * computed earlier.
 *
 * 'final_target' is the query's final target list (in PathTarget form)
 * 'have_postponed_srfs' is an output argument, see below
 *
 * The result is the PathTarget to be computed by the plan node immediately
 * below the Sort step (and the Distinct step, if any).  This will be
 * exactly final_target if we decide a projection step wouldn't be helpful.
 *
 * In addition, *have_postponed_srfs is set to true if we choose to postpone
 * any set-returning functions to after the Sort.
 */
static PathTarget *
make_sort_input_target(PlannerInfo *root,
                       PathTarget *final_target,
                       bool *have_postponed_srfs)
{
    Query      *parse = root->parse;
    PathTarget *input_target;
    int         ncols;
    bool       *col_is_srf;
    bool       *postpone_col;
    bool        have_srf;
    bool        have_volatile;
    bool        have_expensive;
    bool        have_srf_sortcols;
    bool        postpone_srfs;
    List       *postponable_cols;
    List       *postponable_vars;
    int         i;
    ListCell   *lc;

    /* Shouldn't get here unless query has ORDER BY */
    Assert(parse->sortClause);

    *have_postponed_srfs = false;   /* default result */

    /* Inspect tlist and collect per-column information */
    ncols = list_length(final_target->exprs);
    col_is_srf = (bool *) palloc0(ncols * sizeof(bool));
    postpone_col = (bool *) palloc0(ncols * sizeof(bool));
    have_srf = have_volatile = have_expensive = have_srf_sortcols = false;

    i = 0;
    foreach(lc, final_target->exprs)
    {
        Expr       *expr = (Expr *) lfirst(lc);

        /*
         * If the column has a sortgroupref, assume it has to be evaluated
         * before sorting.  Generally such columns would be ORDER BY, GROUP
         * BY, etc targets.  One exception is columns that were removed from
         * GROUP BY by remove_useless_groupby_columns() ... but those would
         * only be Vars anyway.  There don't seem to be any cases where it
         * would be worth the trouble to double-check.
         */
        if (get_pathtarget_sortgroupref(final_target, i) == 0)
        {
            /*
             * Check for SRF or volatile functions.  Check the SRF case first
             * because we must know whether we have any postponed SRFs.
             */
            if (parse->hasTargetSRFs &&
                expression_returns_set((Node *) expr))
            {
                /* We'll decide below whether these are postponable */
                col_is_srf[i] = true;
                have_srf = true;
            }
            else if (contain_volatile_functions((Node *) expr))
            {
                /* Unconditionally postpone */
                postpone_col[i] = true;
                have_volatile = true;
            }
            else
            {
                /*
                 * Else check the cost.  XXX it's annoying to have to do this
                 * when set_pathtarget_cost_width() just did it.  Refactor to
                 * allow sharing the work?
                 */
                QualCost    cost;

                cost_qual_eval_node(&cost, (Node *) expr, root);

                /*
                 * We arbitrarily define "expensive" as "more than 10X
                 * cpu_operator_cost".  Note this will take in any PL function
                 * with default cost.
                 */
                if (cost.per_tuple > 10 * cpu_operator_cost)
                {
                    postpone_col[i] = true;
                    have_expensive = true;
                }
            }
        }
        else
        {
            /* For sortgroupref cols, just check if any contain SRFs */
            if (!have_srf_sortcols &&
                parse->hasTargetSRFs &&
                expression_returns_set((Node *) expr))
                have_srf_sortcols = true;
        }

        i++;
    }

    /*
     * We can postpone SRFs if we have some but none are in sortgroupref cols.
     */
    postpone_srfs = (have_srf && !have_srf_sortcols);

    /*
     * If we don't need a post-sort projection, just return final_target.
     */
    if (!(postpone_srfs || have_volatile ||
          (have_expensive &&
           (parse->limitCount || root->tuple_fraction > 0))))
        return final_target;

    /*
     * Report whether the post-sort projection will contain set-returning
     * functions.  This is important because it affects whether the Sort can
     * rely on the query's LIMIT (if any) to bound the number of rows it needs
     * to return.
     */
    *have_postponed_srfs = postpone_srfs;

    /*
     * Construct the sort-input target, taking all non-postponable columns and
     * then adding Vars, PlaceHolderVars, Aggrefs, and WindowFuncs found in
     * the postponable ones.
     */
    input_target = create_empty_pathtarget();
    postponable_cols = NIL;

    i = 0;
    foreach(lc, final_target->exprs)
    {
        Expr       *expr = (Expr *) lfirst(lc);

        if (postpone_col[i] || (postpone_srfs && col_is_srf[i]))
            postponable_cols = lappend(postponable_cols, expr);
        else
            add_column_to_pathtarget(input_target, expr,
                                     get_pathtarget_sortgroupref(final_target, i));

        i++;
    }

    /*
     * Pull out all the Vars, Aggrefs, and WindowFuncs mentioned in
     * postponable columns, and add them to the sort-input target if not
     * already present.  (Some might be there already.)  We mustn't
     * deconstruct Aggrefs or WindowFuncs here, since the projection node
     * would be unable to recompute them.
     */
    postponable_vars = pull_var_clause((Node *) postponable_cols,
                                       PVC_INCLUDE_AGGREGATES |
                                       PVC_INCLUDE_WINDOWFUNCS |
                                       PVC_INCLUDE_PLACEHOLDERS);
    add_new_columns_to_pathtarget(input_target, postponable_vars);

    /* clean up cruft */
    list_free(postponable_vars);
    list_free(postponable_cols);

    /* XXX this represents even more redundant cost calculation ... */
    return set_pathtarget_cost_width(root, input_target);
}

/*
 * get_cheapest_fractional_path
 *    Find the cheapest path for retrieving a specified fraction of all
 *    the tuples expected to be returned by the given relation.
 *
 * We interpret tuple_fraction the same way as grouping_planner.
 *
 * We assume set_cheapest() has been run on the given rel.
 */
Path *
get_cheapest_fractional_path(RelOptInfo *rel, double tuple_fraction)
{
    Path       *best_path = rel->cheapest_total_path;
    ListCell   *l;

    /* If all tuples will be retrieved, just return the cheapest-total path */
    if (tuple_fraction <= 0.0)
        return best_path;

    /* Convert absolute # of tuples to a fraction; no need to clamp to 0..1 */
    if (tuple_fraction >= 1.0 && best_path->rows > 0)
        tuple_fraction /= best_path->rows;

    foreach(l, rel->pathlist)
    {
        Path       *path = (Path *) lfirst(l);

        if (path == rel->cheapest_total_path ||
            compare_fractional_path_costs(best_path, path, tuple_fraction) <= 0)
            continue;

        best_path = path;
    }

    return best_path;
}

/*
 * adjust_paths_for_srfs
 *      Fix up the Paths of the given upperrel to handle tSRFs properly.
 *
 * The executor can only handle set-returning functions that appear at the
 * top level of the targetlist of a ProjectSet plan node.  If we have any SRFs
 * that are not at top level, we need to split up the evaluation into multiple
 * plan levels in which each level satisfies this constraint.  This function
 * modifies each Path of an upperrel that (might) compute any SRFs in its
 * output tlist to insert appropriate projection steps.
 *
 * The given targets and targets_contain_srfs lists are from
 * split_pathtarget_at_srfs().  We assume the existing Paths emit the first
 * target in targets.
 */
static void
adjust_paths_for_srfs(PlannerInfo *root, RelOptInfo *rel,
                      List *targets, List *targets_contain_srfs)
{
    ListCell   *lc;

    Assert(list_length(targets) == list_length(targets_contain_srfs));
    Assert(!linitial_int(targets_contain_srfs));

    /* If no SRFs appear at this plan level, nothing to do */
    if (list_length(targets) == 1)
        return;

    /*
     * Stack SRF-evaluation nodes atop each path for the rel.
     *
     * In principle we should re-run set_cheapest() here to identify the
     * cheapest path, but it seems unlikely that adding the same tlist eval
     * costs to all the paths would change that, so we don't bother. Instead,
     * just assume that the cheapest-startup and cheapest-total paths remain
     * so.  (There should be no parameterized paths anymore, so we needn't
     * worry about updating cheapest_parameterized_paths.)
     */
    foreach(lc, rel->pathlist)
    {
        Path       *subpath = (Path *) lfirst(lc);
        Path       *newpath = subpath;
        ListCell   *lc1,
                   *lc2;

        Assert(subpath->param_info == NULL);
        forboth(lc1, targets, lc2, targets_contain_srfs)
        {
            PathTarget *thistarget = lfirst_node(PathTarget, lc1);
            bool        contains_srfs = (bool) lfirst_int(lc2);

            /* If this level doesn't contain SRFs, do regular projection */
            if (contains_srfs)
                newpath = (Path *) create_set_projection_path(root,
                                                              rel,
                                                              newpath,
                                                              thistarget);
            else
                newpath = (Path *) apply_projection_to_path(root,
                                                            rel,
                                                            newpath,
                                                            thistarget);
        }
        lfirst(lc) = newpath;
        if (subpath == rel->cheapest_startup_path)
            rel->cheapest_startup_path = newpath;
        if (subpath == rel->cheapest_total_path)
            rel->cheapest_total_path = newpath;
    }

    /* Likewise for partial paths, if any */
    foreach(lc, rel->partial_pathlist)
    {
        Path       *subpath = (Path *) lfirst(lc);
        Path       *newpath = subpath;
        ListCell   *lc1,
                   *lc2;

        Assert(subpath->param_info == NULL);
        forboth(lc1, targets, lc2, targets_contain_srfs)
        {
            PathTarget *thistarget = lfirst_node(PathTarget, lc1);
            bool        contains_srfs = (bool) lfirst_int(lc2);

            /* If this level doesn't contain SRFs, do regular projection */
            if (contains_srfs)
                newpath = (Path *) create_set_projection_path(root,
                                                              rel,
                                                              newpath,
                                                              thistarget);
            else
            {
                /* avoid apply_projection_to_path, in case of multiple refs */
                newpath = (Path *) create_projection_path(root,
                                                          rel,
                                                          newpath,
                                                          thistarget);
            }
        }
        lfirst(lc) = newpath;
    }
}

/*
 * expression_planner
 *      Perform planner's transformations on a standalone expression.
 *
 * Various utility commands need to evaluate expressions that are not part
 * of a plannable query.  They can do so using the executor's regular
 * expression-execution machinery, but first the expression has to be fed
 * through here to transform it from parser output to something executable.
 *
 * Currently, we disallow sublinks in standalone expressions, so there's no
 * real "planning" involved here.  (That might not always be true though.)
 * What we must do is run eval_const_expressions to ensure that any function
 * calls are converted to positional notation and function default arguments
 * get inserted.  The fact that constant subexpressions get simplified is a
 * side-effect that is useful when the expression will get evaluated more than
 * once.  Also, we must fix operator function IDs.
 *
 * This does not return any information about dependencies of the expression.
 * Hence callers should use the results only for the duration of the current
 * query.  Callers that would like to cache the results for longer should use
 * expression_planner_with_deps, probably via the plancache.
 *
 * Note: this must not make any damaging changes to the passed-in expression
 * tree.  (It would actually be okay to apply fix_opfuncids to it, but since
 * we first do an expression_tree_mutator-based walk, what is returned will
 * be a new node tree.)  The result is constructed in the current memory
 * context; beware that this can leak a lot of additional stuff there, too.
 */
Expr *
expression_planner(Expr *expr)
{
    Node       *result;

    /*
     * Convert named-argument function calls, insert default arguments and
     * simplify constant subexprs
     */
    result = eval_const_expressions(NULL, (Node *) expr);

    /* Fill in opfuncid values if missing */
    fix_opfuncids(result);

    return (Expr *) result;
}

/*
 * expression_planner_with_deps
 *      Perform planner's transformations on a standalone expression,
 *      returning expression dependency information along with the result.
 *
 * This is identical to expression_planner() except that it also returns
 * information about possible dependencies of the expression, ie identities of
 * objects whose definitions affect the result.  As in a PlannedStmt, these
 * are expressed as a list of relation Oids and a list of PlanInvalItems.
 */
Expr *
expression_planner_with_deps(Expr *expr,
                             List **relationOids,
                             List **invalItems)
{
    Node       *result;
    PlannerGlobal glob;
    PlannerInfo root;

    /* Make up dummy planner state so we can use setrefs machinery */
    MemSet(&glob, 0, sizeof(glob));
    glob.type = T_PlannerGlobal;
    glob.relationOids = NIL;
    glob.invalItems = NIL;

    MemSet(&root, 0, sizeof(root));
    root.type = T_PlannerInfo;
    root.glob = &glob;

    /*
     * Convert named-argument function calls, insert default arguments and
     * simplify constant subexprs.  Collect identities of inlined functions
     * and elided domains, too.
     */
    result = eval_const_expressions(&root, (Node *) expr);

    /* Fill in opfuncid values if missing */
    fix_opfuncids(result);

    /*
     * Now walk the finished expression to find anything else we ought to
     * record as an expression dependency.
     */
    (void) extract_query_dependencies_walker(result, &root);

    *relationOids = glob.relationOids;
    *invalItems = glob.invalItems;

    return (Expr *) result;
}


/*
 * plan_cluster_use_sort
 *      Use the planner to decide how CLUSTER should implement sorting
 *
 * tableOid is the OID of a table to be clustered on its index indexOid
 * (which is already known to be a btree index).  Decide whether it's
 * cheaper to do an indexscan or a seqscan-plus-sort to execute the CLUSTER.
 * Return true to use sorting, false to use an indexscan.
 *
 * Note: caller had better already hold some type of lock on the table.
 */
bool
plan_cluster_use_sort(Oid tableOid, Oid indexOid)