planner.c

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/*-------------------------------------------------------------------------
 *
 * planner.c
 *    The query optimizer external interface.
 *
 * Portions Copyright (c) 1996-2017, 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/htup_details.h"
#include "access/parallel.h"
#include "access/sysattr.h"
#include "access/xact.h"
#include "catalog/pg_constraint_fn.h"
#include "catalog/pg_proc.h"
#include "catalog/pg_type.h"
#include "executor/executor.h"
#include "executor/nodeAgg.h"
#include "foreign/fdwapi.h"
#include "miscadmin.h"
#include "lib/bipartite_match.h"
#include "lib/knapsack.h"
#include "nodes/makefuncs.h"
#include "nodes/nodeFuncs.h"
#ifdef OPTIMIZER_DEBUG
#include "nodes/print.h"
#endif
#include "optimizer/clauses.h"
#include "optimizer/cost.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 "optimizer/var.h"
#include "parser/analyze.h"
#include "parser/parsetree.h"
#include "parser/parse_agg.h"
#include "rewrite/rewriteManip.h"
#include "storage/dsm_impl.h"
#include "utils/rel.h"
#include "utils/selfuncs.h"
#include "utils/lsyscache.h"
#include "utils/syscache.h"


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

/* 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       *tlist;          /* preprocessed query targetlist */
    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;

/* Local functions */
static Node *preprocess_expression(PlannerInfo *root, Node *expr, int kind);
static void preprocess_qual_conditions(PlannerInfo *root, Node *jtnode);
static void inheritance_planner(PlannerInfo *root);
static void grouping_planner(PlannerInfo *root, bool inheritance_update,
                 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 bool limit_needed(Query *parse);
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);
static Size estimate_hashagg_tablesize(Path *path,
                           const AggClauseCosts *agg_costs,
                           double dNumGroups);
static RelOptInfo *create_grouping_paths(PlannerInfo *root,
                      RelOptInfo *input_rel,
                      PathTarget *target,
                      const AggClauseCosts *agg_costs,
                      grouping_sets_data *gd);
static void consider_groupingsets_paths(PlannerInfo *root,
                            RelOptInfo *grouped_rel,
                            Path *path,
                            bool is_sorted,
                            bool can_hash,
                            PathTarget *target,
                            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,
                    List *tlist,
                    WindowFuncLists *wflists,
                    List *activeWindows);
static void create_one_window_path(PlannerInfo *root,
                       RelOptInfo *window_rel,
                       Path *path,
                       PathTarget *input_target,
                       PathTarget *output_target,
                       List *tlist,
                       WindowFuncLists *wflists,
                       List *activeWindows);
static RelOptInfo *create_distinct_paths(PlannerInfo *root,
                      RelOptInfo *input_rel);
static RelOptInfo *create_ordered_paths(PlannerInfo *root,
                     RelOptInfo *input_rel,
                     PathTarget *target,
                     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);
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);


/*****************************************************************************
 *
 *     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, int cursorOptions, ParamListInfo boundParams)
{
    PlannedStmt *result;

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

PlannedStmt *
standard_planner(Query *parse, 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->nonleafResultRelations = NIL;
    glob->rootResultRelations = NIL;
    glob->relationOids = NIL;
    glob->invalItems = NIL;
    glob->nParamExec = 0;
    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.
     *
     * 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.
     *
     * We can't use parallelism in serializable mode because the predicate
     * locking code is not parallel-aware.  It's not catastrophic if someone
     * tries to run a parallel plan in serializable mode; it just won't get
     * any workers and will run serially.  But it seems like a good heuristic
     * to assume that the same serialization level will be in effect at plan
     * time and execution time, so don't generate a parallel plan if we're in
     * serializable mode.
     */
    if ((cursorOptions & CURSOR_OPT_PARALLEL_OK) != 0 &&
        IsUnderPostmaster &&
        dynamic_shared_memory_type != DSM_IMPL_NONE &&
        parse->commandType == CMD_SELECT &&
        !parse->hasModifyingCTE &&
        max_parallel_workers_per_gather > 0 &&
        !IsParallelWorker() &&
        !IsolationIsSerializable())
    {
        /* 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
     * labelled 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);

        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);

        /*
         * 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->nParamExec > 0)
    {
        Assert(list_length(glob->subplans) == list_length(glob->subroots));
        forboth(lp, glob->subplans, lr, glob->subroots)
        {
            Plan       *subplan = (Plan *) lfirst(lp);
            PlannerInfo *subroot = (PlannerInfo *) lfirst(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->nonleafResultRelations == NIL);
    Assert(glob->rootResultRelations == 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 = (PlannerInfo *) lfirst(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->nonleafResultRelations = glob->nonleafResultRelations;
    result->rootResultRelations = glob->rootResultRelations;
    result->subplans = glob->subplans;
    result->rewindPlanIDs = glob->rewindPlanIDs;
    result->rowMarks = glob->finalrowmarks;
    result->relationOids = glob->relationOids;
    result->invalItems = glob->invalItems;
    result->nParamExec = glob->nParamExec;
    /* 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;

    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;
    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->append_rel_list = NIL;
    root->pcinfo_list = 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->grouping_map = NULL;
    root->minmax_aggs = NIL;
    root->qual_security_level = 0;
    root->hasInheritedTarget = false;
    root->hasRecursion = hasRecursion;
    if (hasRecursion)
        root->wt_param_id = SS_assign_special_param(root);
    else
        root->wt_param_id = -1;
    root->non_recursive_path = NULL;

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

    /*
     * 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 set-returning functions, and inline them if
     * possible (producing subqueries that might get pulled up next).
     * Recursion issues here are handled in the same way as for SubLinks.
     */
    inline_set_returning_functions(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);

    /*
     * Detect whether any rangetable entries are RTE_JOIN kind; if not, we can
     * avoid the expense of doing flatten_join_alias_vars().  Also check for
     * outer joins --- if none, we can skip reduce_outer_joins().  And check
     * for LATERAL RTEs, too.  This must be done after we have done
     * pull_up_subqueries(), of course.
     */
    root->hasJoinRTEs = false;
    root->hasLateralRTEs = false;
    hasOuterJoins = false;
    foreach(l, parse->rtable)
    {
        RangeTblEntry *rte = (RangeTblEntry *) lfirst(l);

        if (rte->rtekind == RTE_JOIN)
        {
            root->hasJoinRTEs = true;
            if (IS_OUTER_JOIN(rte->jointype))
                hasOuterJoins = true;
        }
        if (rte->lateral)
            root->hasLateralRTEs = true;
    }

    /*
     * Preprocess RowMark information.  We need to do this after subquery
     * pullup (so that all non-inherited RTEs are present) and before
     * inheritance expansion (so that the info is available for
     * expand_inherited_tables to examine and modify).
     */
    preprocess_rowmarks(root);

    /*
     * Expand any rangetable entries that are inheritance sets into "append
     * relations".  This can add entries to the rangetable, but they must be
     * plain base relations not joins, so it's OK (and marginally more
     * efficient) to do it after checking for join RTEs.  We must do it after
     * pulling up subqueries, else we'd fail to handle inherited tables in
     * subqueries.
     */
    expand_inherited_tables(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);

    /* Clear this flag; might get set in distribute_qual_to_rels */
    root->hasPseudoConstantQuals = false;

    /*
     * 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 = (WithCheckOption *) lfirst(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 = (WindowClause *) lfirst(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 = (RangeTblEntry *) lfirst(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, (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);
        }
    }

    /*
     * 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);

    /*
     * Do the main planning.  If we have an inherited target relation, that
     * needs special processing, else go straight to grouping_planner.
     */
    if (parse->resultRelation &&
        rt_fetch(parse->resultRelation, parse->rtable)->inh)
        inheritance_planner(root);
    else
        grouping_planner(root, false, 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 before sublink processing,
     * else sublinks expanded out from join aliases would not get processed.
     * We can skip it in non-lateral RTE functions, VALUES lists, and
     * TABLESAMPLE clauses, however, 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, expr);

    /*
     * Simplify constant expressions.
     *
     * 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.
     */
    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);

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

    /* 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);
}

/*
 * inheritance_planner
 *    Generate Paths in the case where the result relation is an
 *    inheritance set.
 *
 * We have to handle this case differently from cases where a source relation
 * is an inheritance set. Source inheritance is expanded at the bottom of the
 * plan tree (see allpaths.c), but target inheritance has to be expanded at
 * the top.  The reason is that for UPDATE, each target relation needs a
 * different targetlist matching its own column set.  Fortunately,
 * the UPDATE/DELETE target can never be the nullable side of an outer join,
 * so it's OK to generate the plan this way.
 *
 * Returns nothing; the useful output is in the Paths we attach to
 * the (UPPERREL_FINAL, NULL) upperrel stored in *root.
 *
 * Note that we have not done set_cheapest() on the final rel; it's convenient
 * to leave this to the caller.
 */
static void
inheritance_planner(PlannerInfo *root)
{
    Query      *parse = root->parse;
    int         parentRTindex = parse->resultRelation;
    Bitmapset  *subqueryRTindexes;
    Bitmapset  *modifiableARIindexes;
    int         nominalRelation = -1;
    List       *final_rtable = NIL;
    int         save_rel_array_size = 0;
    RelOptInfo **save_rel_array = NULL;
    List       *subpaths = NIL;
    List       *subroots = NIL;
    List       *resultRelations = NIL;
    List       *withCheckOptionLists = NIL;
    List       *returningLists = NIL;
    List       *rowMarks;
    RelOptInfo *final_rel;
    ListCell   *lc;
    Index       rti;
    RangeTblEntry *parent_rte;
    List       *partitioned_rels = NIL;

    Assert(parse->commandType != CMD_INSERT);

    /*
     * We generate a modified instance of the original Query for each target
     * relation, plan that, and put all the plans into a list that will be
     * controlled by a single ModifyTable node.  All the instances share the
     * same rangetable, but each instance must have its own set of subquery
     * RTEs within the finished rangetable because (1) they are likely to get
     * scribbled on during planning, and (2) it's not inconceivable that
     * subqueries could get planned differently in different cases.  We need
     * not create duplicate copies of other RTE kinds, in particular not the
     * target relations, because they don't have either of those issues.  Not
     * having to duplicate the target relations is important because doing so
     * (1) would result in a rangetable of length O(N^2) for N targets, with
     * at least O(N^3) work expended here; and (2) would greatly complicate
     * management of the rowMarks list.
     *
     * To begin with, generate a bitmapset of the relids of the subquery RTEs.
     */
    subqueryRTindexes = NULL;
    rti = 1;
    foreach(lc, parse->rtable)
    {
        RangeTblEntry *rte = (RangeTblEntry *) lfirst(lc);

        if (rte->rtekind == RTE_SUBQUERY)
            subqueryRTindexes = bms_add_member(subqueryRTindexes, rti);
        rti++;
    }

    /*
     * Next, we want to identify which AppendRelInfo items contain references
     * to any of the aforesaid subquery RTEs.  These items will need to be
     * copied and modified to adjust their subquery references; whereas the
     * other ones need not be touched.  It's worth being tense over this
     * because we can usually avoid processing most of the AppendRelInfo
     * items, thereby saving O(N^2) space and time when the target is a large
     * inheritance tree.  We can identify AppendRelInfo items by their
     * child_relid, since that should be unique within the list.
     */
    modifiableARIindexes = NULL;
    if (subqueryRTindexes != NULL)
    {
        foreach(lc, root->append_rel_list)
        {
            AppendRelInfo *appinfo = (AppendRelInfo *) lfirst(lc);

            if (bms_is_member(appinfo->parent_relid, subqueryRTindexes) ||
                bms_is_member(appinfo->child_relid, subqueryRTindexes) ||
                bms_overlap(pull_varnos((Node *) appinfo->translated_vars),
                            subqueryRTindexes))
                modifiableARIindexes = bms_add_member(modifiableARIindexes,
                                                      appinfo->child_relid);
        }
    }

    /*
     * If the parent RTE is a partitioned table, we should use that as the
     * nominal relation, because the RTEs added for partitioned tables
     * (including the root parent) as child members of the inheritance set do
     * not appear anywhere else in the plan.  The situation is exactly the
     * opposite in the case of non-partitioned inheritance parent as described
     * below.
     */
    parent_rte = rt_fetch(parentRTindex, root->parse->rtable);
    if (parent_rte->relkind == RELKIND_PARTITIONED_TABLE)
        nominalRelation = parentRTindex;

    /*
     * And now we can get on with generating a plan for each child table.
     */
    foreach(lc, root->append_rel_list)
    {
        AppendRelInfo *appinfo = (AppendRelInfo *) lfirst(lc);
        PlannerInfo *subroot;
        RangeTblEntry *child_rte;
        RelOptInfo *sub_final_rel;
        Path       *subpath;

        /* append_rel_list contains all append rels; ignore others */
        if (appinfo->parent_relid != parentRTindex)
            continue;

        /*
         * We need a working copy of the PlannerInfo so that we can control
         * propagation of information back to the main copy.
         */
        subroot = makeNode(PlannerInfo);
        memcpy(subroot, root, sizeof(PlannerInfo));

        /*
         * Generate modified query with this rel as target.  We first apply
         * adjust_appendrel_attrs, which copies the Query and changes
         * references to the parent RTE to refer to the current child RTE,
         * then fool around with subquery RTEs.
         */
        subroot->parse = (Query *)
            adjust_appendrel_attrs(root,
                                   (Node *) parse,
                                   1, &appinfo);

        /*
         * If there are securityQuals attached to the parent, move them to the
         * child rel (they've already been transformed properly for that).
         */
        parent_rte = rt_fetch(parentRTindex, subroot->parse->rtable);
        child_rte = rt_fetch(appinfo->child_relid, subroot->parse->rtable);
        child_rte->securityQuals = parent_rte->securityQuals;
        parent_rte->securityQuals = NIL;

        /*
         * The rowMarks list might contain references to subquery RTEs, so
         * make a copy that we can apply ChangeVarNodes to.  (Fortunately, the
         * executor doesn't need to see the modified copies --- we can just
         * pass it the original rowMarks list.)
         */
        subroot->rowMarks = copyObject(root->rowMarks);

        /*
         * The append_rel_list likewise might contain references to subquery
         * RTEs (if any subqueries were flattenable UNION ALLs).  So prepare
         * to apply ChangeVarNodes to that, too.  As explained above, we only
         * want to copy items that actually contain such references; the rest
         * can just get linked into the subroot's append_rel_list.
         *
         * If we know there are no such references, we can just use the outer
         * append_rel_list unmodified.
         */
        if (modifiableARIindexes != NULL)
        {
            ListCell   *lc2;

            subroot->append_rel_list = NIL;
            foreach(lc2, root->append_rel_list)
            {
                AppendRelInfo *appinfo2 = (AppendRelInfo *) lfirst(lc2);

                if (bms_is_member(appinfo2->child_relid, modifiableARIindexes))
                    appinfo2 = copyObject(appinfo2);

                subroot->append_rel_list = lappend(subroot->append_rel_list,
                                                   appinfo2);
            }
        }

        /*
         * Add placeholders to the child Query's rangetable list to fill the
         * RT indexes already reserved for subqueries in previous children.
         * These won't be referenced, so there's no need to make them very
         * valid-looking.
         */
        while (list_length(subroot->parse->rtable) < list_length(final_rtable))
            subroot->parse->rtable = lappend(subroot->parse->rtable,
                                             makeNode(RangeTblEntry));

        /*
         * If this isn't the first child Query, generate duplicates of all
         * subquery RTEs, and adjust Var numbering to reference the
         * duplicates. To simplify the loop logic, we scan the original rtable
         * not the copy just made by adjust_appendrel_attrs; that should be OK
         * since subquery RTEs couldn't contain any references to the target
         * rel.
         */
        if (final_rtable != NIL && subqueryRTindexes != NULL)
        {
            ListCell   *lr;

            rti = 1;
            foreach(lr, parse->rtable)
            {
                RangeTblEntry *rte = (RangeTblEntry *) lfirst(lr);

                if (bms_is_member(rti, subqueryRTindexes))
                {
                    Index       newrti;

                    /*
                     * The RTE can't contain any references to its own RT
                     * index, except in its securityQuals, so we can save a
                     * few cycles by applying ChangeVarNodes to the rest of
                     * the rangetable before we append the RTE to it.
                     */
                    newrti = list_length(subroot->parse->rtable) + 1;
                    ChangeVarNodes((Node *) subroot->parse, rti, newrti, 0);
                    ChangeVarNodes((Node *) subroot->rowMarks, rti, newrti, 0);
                    /* Skip processing unchanging parts of append_rel_list */
                    if (modifiableARIindexes != NULL)
                    {
                        ListCell   *lc2;

                        foreach(lc2, subroot->append_rel_list)
                        {
                            AppendRelInfo *appinfo2 = (AppendRelInfo *) lfirst(lc2);

                            if (bms_is_member(appinfo2->child_relid,
                                              modifiableARIindexes))
                                ChangeVarNodes((Node *) appinfo2, rti, newrti, 0);
                        }
                    }
                    rte = copyObject(rte);
                    ChangeVarNodes((Node *) rte->securityQuals, rti, newrti, 0);
                    subroot->parse->rtable = lappend(subroot->parse->rtable,
                                                     rte);
                }
                rti++;
            }
        }

        /* There shouldn't be any OJ info to translate, as yet */
        Assert(subroot->join_info_list == NIL);
        /* and we haven't created PlaceHolderInfos, either */
        Assert(subroot->placeholder_list == NIL);
        /* hack to mark target relation as an inheritance partition */
        subroot->hasInheritedTarget = true;

        /* Generate Path(s) for accessing this result relation */
        grouping_planner(subroot, true, 0.0 /* retrieve all tuples */ );

        /*
         * Set the nomimal target relation of the ModifyTable node if not
         * already done.  We use the inheritance parent RTE as the nominal
         * target relation if it's a partitioned table (see just above this
         * loop).  In the non-partitioned parent case, we'll use the first
         * child relation (even if it's excluded) as the nominal target
         * relation.  Because of the way expand_inherited_rtentry works, the
         * latter should be the RTE representing the parent table in its role
         * as a simple member of the inheritance set.
         *
         * It would be logically cleaner to *always* use the inheritance
         * parent RTE as the nominal relation; but that RTE is not otherwise
         * referenced in the plan in the non-partitioned inheritance case.
         * Instead the duplicate child RTE created by expand_inherited_rtentry
         * is used elsewhere in the plan, so using the original parent RTE
         * would give rise to confusing use of multiple aliases in EXPLAIN
         * output for what the user will think is the "same" table.  OTOH,
         * it's not a problem in the partitioned inheritance case, because the
         * duplicate child RTE added for the parent does not appear anywhere
         * else in the plan tree.
         */
        if (nominalRelation < 0)
            nominalRelation = appinfo->child_relid;

        /*
         * Select cheapest path in case there's more than one.  We always run
         * modification queries to conclusion, so we care only for the
         * cheapest-total path.
         */
        sub_final_rel = fetch_upper_rel(subroot, UPPERREL_FINAL, NULL);
        set_cheapest(sub_final_rel);
        subpath = sub_final_rel->cheapest_total_path;

        /*
         * If this child rel was excluded by constraint exclusion, exclude it
         * from the result plan.
         */
        if (IS_DUMMY_PATH(subpath))
            continue;

        /*
         * If this is the first non-excluded child, its post-planning rtable
         * becomes the initial contents of final_rtable; otherwise, append
         * just its modified subquery RTEs to final_rtable.
         */
        if (final_rtable == NIL)
            final_rtable = subroot->parse->rtable;
        else
            final_rtable = list_concat(final_rtable,
                                       list_copy_tail(subroot->parse->rtable,
                                                      list_length(final_rtable)));

        /*
         * We need to collect all the RelOptInfos from all child plans into
         * the main PlannerInfo, since setrefs.c will need them.  We use the
         * last child's simple_rel_array (previous ones are too short), so we
         * have to propagate forward the RelOptInfos that were already built
         * in previous children.
         */
        Assert(subroot->simple_rel_array_size >= save_rel_array_size);
        for (rti = 1; rti < save_rel_array_size; rti++)
        {
            RelOptInfo *brel = save_rel_array[rti];

            if (brel)
                subroot->simple_rel_array[rti] = brel;
        }
        save_rel_array_size = subroot->simple_rel_array_size;
        save_rel_array = subroot->simple_rel_array;

        /* Make sure any initplans from this rel get into the outer list */
        root->init_plans = subroot->init_plans;

        /* Build list of sub-paths */
        subpaths = lappend(subpaths, subpath);

        /* Build list of modified subroots, too */
        subroots = lappend(subroots, subroot);

        /* Build list of target-relation RT indexes */
        resultRelations = lappend_int(resultRelations, appinfo->child_relid);

        /* Build lists of per-relation WCO and RETURNING targetlists */
        if (parse->withCheckOptions)
            withCheckOptionLists = lappend(withCheckOptionLists,
                                           subroot->parse->withCheckOptions);
        if (parse->returningList)
            returningLists = lappend(returningLists,
                                     subroot->parse->returningList);

        Assert(!parse->onConflict);
    }

    if (parent_rte->relkind == RELKIND_PARTITIONED_TABLE)
    {
        partitioned_rels = get_partitioned_child_rels(root, parentRTindex);
        /* The root partitioned table is included as a child rel */
        Assert(list_length(partitioned_rels) >= 1);
    }

    /* Result path must go into outer query's FINAL upperrel */
    final_rel = fetch_upper_rel(root, UPPERREL_FINAL, NULL);

    /*
     * We don't currently worry about setting final_rel's consider_parallel
     * flag in this case, nor about allowing FDWs or create_upper_paths_hook
     * to get control here.
     */

    /*
     * If we managed to exclude every child rel, return a dummy plan; it
     * doesn't even need a ModifyTable node.
     */
    if (subpaths == NIL)
    {
        set_dummy_rel_pathlist(final_rel);
        return;
    }

    /*
     * Put back the final adjusted rtable into the master copy of the Query.
     * (We mustn't do this if we found no non-excluded children.)
     */
    parse->rtable = final_rtable;
    root->simple_rel_array_size = save_rel_array_size;
    root->simple_rel_array = save_rel_array;
    /* Must reconstruct master's simple_rte_array, too */
    root->simple_rte_array = (RangeTblEntry **)
        palloc0((list_length(final_rtable) + 1) * sizeof(RangeTblEntry *));
    rti = 1;
    foreach(lc, final_rtable)
    {
        RangeTblEntry *rte = (RangeTblEntry *) lfirst(lc);

        root->simple_rte_array[rti++] = rte;
    }

    /*
     * 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;

    /* Create Path representing a ModifyTable to do the UPDATE/DELETE work */
    add_path(final_rel, (Path *)
             create_modifytable_path(root, final_rel,
                                     parse->commandType,
                                     parse->canSetTag,
                                     nominalRelation,
                                     partitioned_rels,
                                     resultRelations,
                                     subpaths,
                                     subroots,
                                     withCheckOptionLists,
                                     returningLists,
                                     rowMarks,
                                     NULL,
                                     SS_assign_special_param(root)));
}

/*--------------------
 * 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.
 *
 * If inheritance_update is true, we're being called from inheritance_planner
 * and should not include a ModifyTable step in the resulting Path(s).
 * (inheritance_planner will create a single ModifyTable node covering all the
 * target tables.)
 *
 * 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, bool inheritance_update,
                 double tuple_fraction)
{
    Query      *parse = root->parse;
    List       *tlist = parse->targetList;
    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;
    RelOptInfo *current_rel;
    RelOptInfo *final_rel;
    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 targetlist 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);

        tlist = root->processed_tlist;  /* from plan_set_operations */

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

        /* Save aside the final decorated tlist */
        root->processed_tlist = tlist;

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

        /* 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(((RowMarkClause *)
                                          linitial(parse->rowMarks))->strength))));

        /*
         * Calculate pathkeys that represent result ordering requirements
         */
        Assert(parse->distinctClause == NIL);
        root->sort_pathkeys = make_pathkeys_for_sortclauses(root,
                                                            parse->sortClause,
                                                            tlist);
    }
    else
    {
        /* No set operations, do regular planning */
        PathTarget *sort_input_target;
        List       *sort_input_targets;
        List       *sort_input_targets_contain_srfs;
        PathTarget *grouping_target;
        List       *grouping_targets;
        List       *grouping_targets_contain_srfs;
        PathTarget *scanjoin_target;
        List       *scanjoin_targets;
        List       *scanjoin_targets_contain_srfs;
        bool        have_grouping;
        AggClauseCosts agg_costs;
        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 */
        tlist = preprocess_targetlist(root, tlist);

        if (parse->onConflict)
            parse->onConflict->onConflictSet =
                preprocess_onconflict_targetlist(parse->onConflict->onConflictSet,
                                                 parse->resultRelation,
                                                 parse->rtable);

        /*
         * We are now done hacking up the query's targetlist.  Most of the
         * remaining planning work will be done with the PathTarget
         * representation of tlists, but save aside the full representation so
         * that we can transfer its decoration (resnames etc) to the topmost
         * tlist of the finished Plan.
         */
        root->processed_tlist = tlist;

        /*
         * Collect statistics about aggregates for estimating costs, and mark
         * all the aggregates with resolved aggtranstypes.  We must do this
         * before slicing and dicing the tlist into various pathtargets, else
         * some copies of the Aggref nodes might escape being marked with the
         * correct transtypes.
         *
         * Note: currently, we do not detect duplicate aggregates here.  This
         * may result in somewhat-overestimated cost, which is fine for our
         * purposes since all Paths will get charged the same.  But at some
         * point we might wish to do that detection in the planner, rather
         * than during executor startup.
         */
        MemSet(&agg_costs, 0, sizeof(AggClauseCosts));
        if (parse->hasAggs)
        {
            get_agg_clause_costs(root, (Node *) tlist, AGGSPLIT_SIMPLE,
                                 &agg_costs);
            get_agg_clause_costs(root, parse->havingQual, AGGSPLIT_SIMPLE,
                                 &agg_costs);
        }

        /*
         * 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 *) 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, tlist);

        /*
         * 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.tlist = tlist;
        qp_extra.activeWindows = activeWindows;
        qp_extra.groupClause = (gset_data
                                ? (gset_data->rollups ? ((RollupData *) linitial(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, tlist,
                                    standard_qp_callback, &qp_extra);

        /*
         * Convert the query's result tlist into PathTarget format.
         *
         * Note: it's desirable to not do this till after query_planner(),
         * because the target width estimates can use per-Var width numbers
         * that were obtained within query_planner().
         */
        final_target = create_pathtarget(root, tlist);

        /*
         * 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);
        else
            sort_input_target = final_target;

        /*
         * 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);
        else
            grouping_target = sort_input_target;

        /*
         * 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);
        else
            scanjoin_target = grouping_target;

        /*
         * 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 = (PathTarget *) linitial(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 = (PathTarget *) linitial(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 = (PathTarget *) linitial(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 = (PathTarget *) linitial(scanjoin_targets);
            Assert(!linitial_int(scanjoin_targets_contain_srfs));
        }
        else
        {
            /* initialize lists, just to keep compiler quiet */
            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 = scanjoin_targets_contain_srfs = NIL;
        }

        /*
         * Forcibly apply SRF-free scan/join target to all the Paths for the
         * scan/join 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, current_rel->pathlist)
        {
            Path       *subpath = (Path *) lfirst(lc);
            Path       *path;

            Assert(subpath->param_info == NULL);
            path = apply_projection_to_path(root, current_rel,
                                            subpath, scanjoin_target);
            /* If we had to add a Result, path is different from subpath */
            if (path != subpath)
            {
                lfirst(lc) = path;
                if (subpath == current_rel->cheapest_startup_path)
                    current_rel->cheapest_startup_path = path;
                if (subpath == current_rel->cheapest_total_path)
                    current_rel->cheapest_total_path = path;
            }
        }

        /*
         * Upper planning steps which make use of the top scan/join rel's
         * partial pathlist will expect partial paths for that rel to produce
         * the same output as complete paths ... and we just changed the
         * output for the complete paths, so we'll need to do the same thing
         * for partial paths.  But only parallel-safe expressions can be
         * computed by partial paths.
         */
        if (current_rel->partial_pathlist &&
            is_parallel_safe(root, (Node *) scanjoin_target->exprs))
        {
            /* Apply the scan/join target to each partial path */
            foreach(lc, current_rel->partial_pathlist)
            {
                Path       *subpath = (Path *) lfirst(lc);
                Path       *newpath;

                /* Shouldn't have any parameterized paths anymore */
                Assert(subpath->param_info == NULL);

                /*
                 * Don't use apply_projection_to_path() here, because there
                 * could be other pointers to these paths, and therefore we
                 * mustn't modify them in place.
                 */
                newpath = (Path *) create_projection_path(root,
                                                          current_rel,
                                                          subpath,
                                                          scanjoin_target);
                lfirst(lc) = newpath;
            }
        }
        else
        {
            /*
             * In the unfortunate event that scanjoin_target is not
             * parallel-safe, we can't apply it to the partial paths; in that
             * case, we'll need to forget about the partial paths, which
             * aren't valid input for upper planning steps.
             */
            current_rel->partial_pathlist = NIL;
        }

        /* Now fix things up if scan/join target contains SRFs */
        if (parse->hasTargetSRFs)
            adjust_paths_for_srfs(root, current_rel,
                                  scanjoin_targets,
                                  scanjoin_targets_contain_srfs);

        /*
         * 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_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,
                                                &agg_costs,
                                                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,
                                              tlist,
                                              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,
                                           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,
                                                 SS_assign_special_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,
                                              offset_est, count_est);
        }

        /*
         * If this is an INSERT/UPDATE/DELETE, and we're not being called from
         * inheritance_planner, add the ModifyTable node.
         */
        if (parse->commandType != CMD_SELECT && !inheritance_update)
        {
            List       *withCheckOptionLists;
            List       *returningLists;
            List       *rowMarks;

            /*
             * Set up the WITH CHECK OPTION and RETURNING lists-of-lists, if
             * needed.
             */
            if (parse->withCheckOptions)
                withCheckOptionLists = list_make1(parse->withCheckOptions);
            else
                withCheckOptionLists = NIL;

            if (parse->returningList)
                returningLists = list_make1(parse->returningList);
            else
                returningLists = NIL;

            /*
             * 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,
                                        parse->commandType,
                                        parse->canSetTag,
                                        parse->resultRelation,
                                        NIL,
                                        list_make1_int(parse->resultRelation),
                                        list_make1(path),
                                        list_make1(root),
                                        withCheckOptionLists,
                                        returningLists,
                                        rowMarks,
                                        parse->onConflict,
                                        SS_assign_special_param(root));
        }

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

    /*
     * 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);

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

    /* 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, -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(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 = 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(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(lc);

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

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

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

        result = lappend(result, set);
    }

    return result;
}



/*
 * Detect whether a plan node is a "dummy" plan created when a relation
 * is deemed not to need scanning due to constraint exclusion.
 *
 * Currently, such dummy plans are Result nodes with constant FALSE
 * filter quals (see set_dummy_rel_pathlist and create_append_plan).
 *
 * XXX this probably ought to be somewhere else, but not clear where.
 */
bool
is_dummy_plan(Plan *plan)
{
    if (IsA(plan, Result))
    {
        List       *rcqual = (List *) ((Result *) plan)->resconstantqual;

        if (list_length(rcqual) == 1)
        {
            Const      *constqual = (Const *) linitial(rcqual);

            if (constqual && IsA(constqual, Const))
            {
                if (!constqual->constisnull &&
                    !DatumGetBool(constqual->constvalue))
                    return true;
            }
        }
    }
    return false;
}

/*
 * 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, ((RowMarkClause *)
                                   linitial(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 = (RowMarkClause *) lfirst(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 = (RangeTblEntry *) lfirst(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.
 */
static 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.  When we do this, we
 * must mark the plan as dependent on the pkey constraint (compare the
 * parser's check_ungrouped_columns() and check_functional_grouping()).
 *
 * In principle, we could treat any NOT-NULL columns appearing in a UNIQUE
 * index as the determining columns.  But as with check_functional_grouping(),
 * there's currently no way to represent dependency on a NOT NULL constraint,
 * so we consider only the pkey for now.
 */
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 = (SortGroupClause *) lfirst(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 = (RangeTblEntry *) lfirst(lc);
        Bitmapset  *relattnos;
        Bitmapset  *pkattnos;
        Oid         constraintOid;

        relid++;

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

            /* Also, mark the resulting plan as dependent on this constraint */
            parse->constraintDeps = lappend_oid(parse->constraintDeps,
                                                constraintOid);
        }
    }

    /*
     * 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 = (SortGroupClause *) lfirst(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 = (SortGroupClause *) lfirst(sl);

        foreach(gl, parse->groupClause)
        {
            SortGroupClause *gc = (SortGroupClause *) lfirst(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 = (SortGroupClause *) lfirst(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(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, lc1)
    {
        List       *candidate = 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;
    ListCell   *lc2;
    List       *previous = NIL;
    List       *result = NIL;

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

        if (list_length(new_elems) > 0)
        {
            while (list_length(sortclause) > list_length(previous))
            {
                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;
                }
            }

            foreach(lc2, new_elems)
            {
                previous = lappend_int(previous, lfirst_int(lc2));
            }
        }

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

    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 = qp_extra->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 = (WindowClause *) linitial(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
 * gsets: grouping set data, or NULL if not doing grouping sets
 *
 * 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)
{
    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(lc);
                ListCell   *lc;

                groupExprs = get_sortgrouplist_exprs(rollup->groupClause,
                                                     parse->targetList);

                rollup->numGroups = 0.0;

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

                    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,
                                                     parse->targetList);

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

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

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

            dNumGroups = estimate_num_groups(root, groupExprs, path_rows,
                                             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;
}

/*
 * estimate_hashagg_tablesize
 *    estimate the number of bytes that a hash aggregate hashtable will
 *    require based on the agg_costs, path width and dNumGroups.
 *
 * XXX this may be over-estimating the size now that hashagg knows to omit
 * unneeded columns from the hashtable. Also for mixed-mode grouping sets,
 * grouping columns not in the hashed set are counted here even though hashagg
 * won't store them. Is this a problem?
 */
static Size
estimate_hashagg_tablesize(Path *path, const AggClauseCosts *agg_costs,
                           double dNumGroups)
{
    Size        hashentrysize;

    /* Estimate per-hash-entry space at tuple width... */
    hashentrysize = MAXALIGN(path->pathtarget->width) +
        MAXALIGN(SizeofMinimalTupleHeader);

    /* plus space for pass-by-ref transition values... */
    hashentrysize += agg_costs->transitionSpace;
    /* plus the per-hash-entry overhead */
    hashentrysize += hash_agg_entry_size(agg_costs->numAggs);

    /*
     * Note that this disregards the effect of fill-factor and growth policy
     * of the hash-table. That's probably ok, given default the default
     * fill-factor is relatively high. It'd be hard to meaningfully factor in
     * "double-in-size" growth policies here.
     */
    return hashentrysize * dNumGroups;
}

/*
 * create_grouping_paths
 *
 * Build a new upperrel containing Paths for grouping and/or aggregation.
 *
 * input_rel: contains the source-data Paths
 * target: the pathtarget for the result Paths to compute
 * agg_costs: cost info about all aggregates in query (in AGGSPLIT_SIMPLE mode)
 * rollup_lists: list of grouping sets, or NIL if not doing grouping sets
 * rollup_groupclauses: list of grouping clauses for grouping sets,
 *      or NIL if not doing grouping sets
 *
 * Note: all Paths in input_rel are expected to return the target computed
 * by make_group_input_target.
 *
 * 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.
 */
static RelOptInfo *
create_grouping_paths(PlannerInfo *root,
                      RelOptInfo *input_rel,
                      PathTarget *target,
                      const AggClauseCosts *agg_costs,
                      grouping_sets_data *gd)
{
    Query      *parse = root->parse;
    Path       *cheapest_path = input_rel->cheapest_total_path;
    RelOptInfo *grouped_rel;
    PathTarget *partial_grouping_target = NULL;
    AggClauseCosts agg_partial_costs;   /* parallel only */
    AggClauseCosts agg_final_costs; /* parallel only */
    Size        hashaggtablesize;
    double      dNumGroups;
    double      dNumPartialGroups = 0;
    bool        can_hash;
    bool        can_sort;
    bool        try_parallel_aggregation;

    ListCell   *lc;

    /* For now, do all work in the (GROUP_AGG, NULL) upperrel */
    grouped_rel = fetch_upper_rel(root, UPPERREL_GROUP_AGG, NULL);

    /*
     * 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 &&
        is_parallel_safe(root, (Node *) target->exprs) &&
        is_parallel_safe(root, (Node *) parse->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;

    /*
     * Check for degenerate grouping.
     */
    if ((root->hasHavingQual || parse->groupingSets) &&
        !parse->hasAggs && parse->groupClause == NIL)
    {
        /*
         * We have a HAVING qual and/or grouping sets, but no aggregates and
         * no GROUP BY (which implies that the grouping sets are all empty).
         *
         * This is a degenerate case in which 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.
         */
        int         nrows = list_length(parse->groupingSets);
        Path       *path;

        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_result_path(root, grouped_rel,
                                       target,
                                       (List *) parse->havingQual);
                paths = lappend(paths, path);
            }
            path = (Path *)
                create_append_path(grouped_rel,
                                   paths,
                                   NULL,
                                   0,
                                   NIL);
            path->pathtarget = target;
        }
        else
        {
            /* No grouping sets, or just one, so one output row */
            path = (Path *)
                create_result_path(root, grouped_rel,
                                   target,
                                   (List *) parse->havingQual);
        }

        add_path(grouped_rel, path);

        /* No need to consider any other alternatives. */
        set_cheapest(grouped_rel);

        return grouped_rel;
    }

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

    /*
     * 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.
     */
    can_sort = (gd && gd->rollups != NIL)
        || grouping_is_sortable(parse->groupClause);

    /*
     * 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.
     */
    can_hash = (parse->groupClause != NIL &&
                agg_costs->numOrderedAggs == 0 &&
                (gd ? gd->any_hashable : grouping_is_hashable(parse->groupClause)));

    /*
     * If grouped_rel->consider_parallel is true, then paths that we generate
     * for this grouping relation could be run inside of a worker, but that
     * doesn't mean we can actually use the PartialAggregate/FinalizeAggregate
     * execution strategy.  Figure that out.
     */
    if (!grouped_rel->consider_parallel)
    {
        /* Not even parallel-safe. */
        try_parallel_aggregation = false;
    }
    else if (input_rel->partial_pathlist == NIL)
    {
        /* Nothing to use as input for partial aggregate. */
        try_parallel_aggregation = false;
    }
    else if (!parse->hasAggs && parse->groupClause == NIL)
    {
        /*
         * We don't know how to do parallel aggregation unless we have either
         * some aggregates or a grouping clause.
         */
        try_parallel_aggregation = false;
    }
    else if (parse->groupingSets)
    {
        /* We don't know how to do grouping sets in parallel. */
        try_parallel_aggregation = false;
    }
    else if (agg_costs->hasNonPartial || agg_costs->hasNonSerial)
    {
        /* Insufficient support for partial mode. */
        try_parallel_aggregation = false;
    }
    else
    {
        /* Everything looks good. */
        try_parallel_aggregation = true;
    }

    /*
     * Before generating paths for grouped_rel, we first generate any possible
     * partial paths; that way, later code can easily consider both parallel
     * and non-parallel approaches to grouping.  Note that the partial paths
     * we generate here are also partially aggregated, so simply pushing a
     * Gather node on top is insufficient to create a final path, as would be
     * the case for a scan/join rel.
     */
    if (try_parallel_aggregation)
    {
        Path       *cheapest_partial_path = linitial(input_rel->partial_pathlist);

        /*
         * Build target list for partial aggregate paths.  These paths cannot
         * just emit the same tlist as regular aggregate paths, because (1) we
         * must include Vars and Aggrefs needed in HAVING, which might not
         * appear in the result tlist, and (2) the Aggrefs must be set in
         * partial mode.
         */
        partial_grouping_target = make_partial_grouping_target(root, target);

        /* Estimate number of partial groups. */
        dNumPartialGroups = get_number_of_groups(root,
                                                 cheapest_partial_path->rows,
                                                 gd);

        /*
         * Collect statistics about aggregates for estimating costs of
         * performing aggregation in parallel.
         */
        MemSet(&agg_partial_costs, 0, sizeof(AggClauseCosts));
        MemSet(&agg_final_costs, 0, sizeof(AggClauseCosts));
        if (parse->hasAggs)
        {
            /* partial phase */
            get_agg_clause_costs(root, (Node *) partial_grouping_target->exprs,
                                 AGGSPLIT_INITIAL_SERIAL,
                                 &agg_partial_costs);

            /* final phase */
            get_agg_clause_costs(root, (Node *) target->exprs,
                                 AGGSPLIT_FINAL_DESERIAL,
                                 &agg_final_costs);
            get_agg_clause_costs(root, parse->havingQual,
                                 AGGSPLIT_FINAL_DESERIAL,
                                 &agg_final_costs);
        }

        if (can_sort)
        {
            /* This was checked before setting try_parallel_aggregation */
            Assert(parse->hasAggs || parse->groupClause);

            /*
             * Use any available suitably-sorted path as input, and also
             * consider sorting the cheapest partial path.
             */
            foreach(lc, input_rel->partial_pathlist)
            {
                Path       *path = (Path *) lfirst(lc);
                bool        is_sorted;

                is_sorted = pathkeys_contained_in(root->group_pathkeys,
                                                  path->pathkeys);
                if (path == cheapest_partial_path || is_sorted)
                {
                    /* Sort the cheapest partial path, if it isn't already */
                    if (!is_sorted)
                        path = (Path *) create_sort_path(root,
                                                         grouped_rel,
                                                         path,
                                                         root->group_pathkeys,
                                                         -1.0);

                    if (parse->hasAggs)
                        add_partial_path(grouped_rel, (Path *)
                                         create_agg_path(root,
                                                         grouped_rel,
                                                         path,
                                                         partial_grouping_target,
                                                         parse->groupClause ? AGG_SORTED : AGG_PLAIN,
                                                         AGGSPLIT_INITIAL_SERIAL,
                                                         parse->groupClause,
                                                         NIL,
                                                         &agg_partial_costs,
                                                         dNumPartialGroups));
                    else
                        add_partial_path(grouped_rel, (Path *)
                                         create_group_path(root,
                                                           grouped_rel,
                                                           path,
                                                           partial_grouping_target,
                                                           parse->groupClause,
                                                           NIL,
                                                           dNumPartialGroups));
                }
            }
        }

        if (can_hash)
        {
            /* Checked above */
            Assert(parse->hasAggs || parse->groupClause);

            hashaggtablesize =
                estimate_hashagg_tablesize(cheapest_partial_path,
                                           &agg_partial_costs,
                                           dNumPartialGroups);

            /*
             * Tentatively produce a partial HashAgg Path, depending on if it
             * looks as if the hash table will fit in work_mem.
             */
            if (hashaggtablesize < work_mem * 1024L)
            {
                add_partial_path(grouped_rel, (Path *)
                                 create_agg_path(root,
                                                 grouped_rel,
                                                 cheapest_partial_path,
                                                 partial_grouping_target,
                                                 AGG_HASHED,
                                                 AGGSPLIT_INITIAL_SERIAL,
                                                 parse->groupClause,
                                                 NIL,
                                                 &agg_partial_costs,
                                                 dNumPartialGroups));
            }
        }
    }

    /* Build final grouping paths */
    if (can_sort)
    {
        /*
         * Use any available suitably-sorted path as input, and also consider
         * sorting the cheapest-total path.
         */
        foreach(lc, input_rel->pathlist)
        {
            Path       *path = (Path *) lfirst(lc);
            bool        is_sorted;

            is_sorted = pathkeys_contained_in(root->group_pathkeys,
                                              path->pathkeys);
            if (path == cheapest_path || is_sorted)
            {
                /* Sort the cheapest-total path if it isn't already sorted */
                if (!is_sorted)
                    path = (Path *) create_sort_path(root,
                                                     grouped_rel,
                                                     path,
                                                     root->group_pathkeys,
                                                     -1.0);

                /* Now decide what to stick atop it */
                if (parse->groupingSets)
                {
                    consider_groupingsets_paths(root, grouped_rel,
                                                path, true, can_hash, target,
                                                gd, agg_costs, dNumGroups);
                }
                else if (parse->hasAggs)
                {
                    /*
                     * We have aggregation, possibly with plain GROUP BY. Make
                     * an AggPath.
                     */
                    add_path(grouped_rel, (Path *)
                             create_agg_path(root,
                                             grouped_rel,
                                             path,
                                             target,
                                             parse->groupClause ? AGG_SORTED : AGG_PLAIN,
                                             AGGSPLIT_SIMPLE,
                                             parse->groupClause,
                                             (List *) parse->havingQual,
                                             agg_costs,
                                             dNumGroups));
                }
                else if (parse->groupClause)
                {
                    /*
                     * We have GROUP BY without aggregation or grouping sets.
                     * Make a GroupPath.
                     */
                    add_path(grouped_rel, (Path *)
                             create_group_path(root,
                                               grouped_rel,
                                               path,
                                               target,
                                               parse->groupClause,
                                               (List *) parse->havingQual,
                                               dNumGroups));
                }
                else
                {
                    /* Other cases should have been handled above */
                    Assert(false);
                }
            }
        }

        /*
         * Now generate a complete GroupAgg Path atop of the cheapest partial
         * path.  We can do this using either Gather or Gather Merge.
         */
        if (grouped_rel->partial_pathlist)
        {
            Path       *path = (Path *) linitial(grouped_rel->partial_pathlist);
            double      total_groups = path->rows * path->parallel_workers;

            path = (Path *) create_gather_path(root,
                                               grouped_rel,
                                               path,
                                               partial_grouping_target,
                                               NULL,
                                               &total_groups);

            /*
             * Since Gather's output is always unsorted, we'll need to sort,
             * unless there's no GROUP BY clause or a degenerate (constant)
             * one, in which case there will only be a single group.
             */
            if (root->group_pathkeys)
                path = (Path *) create_sort_path(root,
                                                 grouped_rel,
                                                 path,
                                                 root->group_pathkeys,
                                                 -1.0);

            if (parse->hasAggs)
                add_path(grouped_rel, (Path *)
                         create_agg_path(root,
                                         grouped_rel,
                                         path,
                                         target,
                                         parse->groupClause ? AGG_SORTED : AGG_PLAIN,
                                         AGGSPLIT_FINAL_DESERIAL,
                                         parse->groupClause,
                                         (List *) parse->havingQual,
                                         &agg_final_costs,
                                         dNumGroups));
            else
                add_path(grouped_rel, (Path *)
                         create_group_path(root,
                                           grouped_rel,
                                           path,
                                           target,
                                           parse->groupClause,
                                           (List *) parse->havingQual,
                                           dNumGroups));

            /*
             * The point of using Gather Merge rather than Gather is that it
             * can preserve the ordering of the input path, so there's no
             * reason to try it unless (1) it's possible to produce more than
             * one output row and (2) we want the output path to be ordered.
             */
            if (parse->groupClause != NIL && root->group_pathkeys != NIL)
            {
                foreach(lc, grouped_rel->partial_pathlist)
                {
                    Path       *subpath = (Path *) lfirst(lc);
                    Path       *gmpath;
                    double      total_groups;

                    /*
                     * It's useful to consider paths that are already properly
                     * ordered for Gather Merge, because those don't need a
                     * sort.  It's also useful to consider the cheapest path,
                     * because sorting it in parallel and then doing Gather
                     * Merge may be better than doing an unordered Gather
                     * followed by a sort.  But there's no point in
                     * considering non-cheapest paths that aren't already
                     * sorted correctly.
                     */
                    if (path != subpath &&
                        !pathkeys_contained_in(root->group_pathkeys,
                                               subpath->pathkeys))
                        continue;

                    total_groups = subpath->rows * subpath->parallel_workers;

                    gmpath = (Path *)
                        create_gather_merge_path(root,
                                                 grouped_rel,
                                                 subpath,
                                                 partial_grouping_target,
                                                 root->group_pathkeys,
                                                 NULL,
                                                 &total_groups);

                    if (parse->hasAggs)
                        add_path(grouped_rel, (Path *)
                                 create_agg_path(root,
                                                 grouped_rel,
                                                 gmpath,
                                                 target,
                                                 parse->groupClause ? AGG_SORTED : AGG_PLAIN,
                                                 AGGSPLIT_FINAL_DESERIAL,
                                                 parse->groupClause,
                                                 (List *) parse->havingQual,
                                                 &agg_final_costs,
                                                 dNumGroups));
                    else
                        add_path(grouped_rel, (Path *)
                                 create_group_path(root,
                                                   grouped_rel,
                                                   gmpath,
                                                   target,
                                                   parse->groupClause,
                                                   (List *) parse->havingQual,
                                                   dNumGroups));
                }
            }
        }
    }

    if (can_hash)
    {
        if (parse->groupingSets)
        {
            /*
             * Try for a hash-only groupingsets path over unsorted input.
             */
            consider_groupingsets_paths(root, grouped_rel,
                                        cheapest_path, false, true, target,
                                        gd, agg_costs, dNumGroups);
        }
        else
        {
            hashaggtablesize = estimate_hashagg_tablesize(cheapest_path,
                                                          agg_costs,
                                                          dNumGroups);

            /*
             * Provided that the estimated size of the hashtable does not
             * exceed work_mem, we'll generate a HashAgg Path, although if we
             * were unable to sort above, then we'd better generate a Path, so
             * that we at least have one.
             */
            if (hashaggtablesize < work_mem * 1024L ||
                grouped_rel->pathlist == NIL)
            {
                /*
                 * We just need an Agg over the cheapest-total input path,
                 * since input order won't matter.
                 */
                add_path(grouped_rel, (Path *)
                         create_agg_path(root, grouped_rel,
                                         cheapest_path,
                                         target,
                                         AGG_HASHED,
                                         AGGSPLIT_SIMPLE,
                                         parse->groupClause,
                                         (List *) parse->havingQual,
                                         agg_costs,
                                         dNumGroups));
            }
        }

        /*
         * Generate a HashAgg Path atop of the cheapest partial path. Once
         * again, we'll only do this if it looks as though the hash table
         * won't exceed work_mem.
         */
        if (grouped_rel->partial_pathlist)
        {
            Path       *path = (Path *) linitial(grouped_rel->partial_pathlist);

            hashaggtablesize = estimate_hashagg_tablesize(path,
                                                          &agg_final_costs,
                                                          dNumGroups);

            if (hashaggtablesize < work_mem * 1024L)
            {
                double      total_groups = path->rows * path->parallel_workers;

                path = (Path *) create_gather_path(root,
                                                   grouped_rel,
                                                   path,
                                                   partial_grouping_target,
                                                   NULL,
                                                   &total_groups);

                add_path(grouped_rel, (Path *)
                         create_agg_path(root,
                                         grouped_rel,
                                         path,
                                         target,
                                         AGG_HASHED,
                                         AGGSPLIT_FINAL_DESERIAL,
                                         parse->groupClause,
                                         (List *) parse->havingQual,
                                         &agg_final_costs,
                                         dNumGroups));
            }
        }
    }

    /* 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);

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

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

    /*
     * We've been using the partial pathlist for the grouped relation to hold
     * partially aggregated paths, but that's actually a little bit bogus
     * because it's unsafe for later planning stages -- like ordered_rel ---
     * to get the idea that they can use these partial paths as if they didn't
     * need a FinalizeAggregate step.  Zap the partial pathlist at this stage
     * so we don't get confused.
     */
    grouped_rel->partial_pathlist = NIL;

    return grouped_rel;
}


/*
 * 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,
                            PathTarget *target,
                            grouping_sets_data *gd,
                            const AggClauseCosts *agg_costs,
                            double dNumGroups)
{
    Query      *parse = root->parse;

    /*
     * 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 work_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 work_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;
        Size        hashsize;
        double      exclude_groups = 0.0;

        Assert(can_hash);

        if (pathkeys_contained_in(root->group_pathkeys, path->pathkeys))
        {
            unhashed_rollup = lfirst(l_start);
            exclude_groups = unhashed_rollup->numGroups;
            l_start = lnext(l_start);
        }

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

        /*
         * gd->rollups is empty if we have only unsortable columns to work
         * with.  Override work_mem in that case; otherwise, we'll rely on the
         * sorted-input case to generate usable mixed paths.
         */
        if (hashsize > work_mem * 1024L && 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, l_start)
        {
            RollupData *rollup = lfirst(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;
            else
                sets_data = list_concat(sets_data, list_copy(rollup->gsets_data));
        }
        foreach(lc, sets_data)
        {
            GroupingSetData *gs = lfirst(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,
                                          target,
                                          (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 = (work_mem * 1024.0);
        ListCell   *lc;

        /*
         * Account first for space needed for groups we can't sort at all.
         */
        availspace -= (double) estimate_hashagg_tablesize(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 work_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_cell(lc, lnext(list_head(gd->rollups)))
            {
                RollupData *rollup = lfirst(lc);

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

                    /*
                     * If sz is enormous, but work_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_cell(lc, lnext(list_head(gd->rollups)))
                {
                    RollupData *rollup = lfirst(lc);

                    if (rollup->hashable)
                    {
                        if (bms_is_member(i, hash_items))
                            hash_sets = list_concat(hash_sets,
                                                    list_copy(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(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,
                                              target,
                                              (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,
                                          target,
                                          (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
 * tlist: query's target list (needed to look up pathkeys)
 * 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,
                    List *tlist,
                    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 &&
        is_parallel_safe(root, (Node *) output_target->exprs) &&
        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 root->window_pathkeys (which won't).
     */
    foreach(lc, input_rel->pathlist)
    {
        Path       *path = (Path *) lfirst(lc);

        if (path == input_rel->cheapest_total_path ||
            pathkeys_contained_in(root->window_pathkeys, path->pathkeys))
            create_one_window_path(root,
                                   window_rel,
                                   path,
                                   input_target,
                                   output_target,
                                   tlist,
                                   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);

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

    /* 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
 * tlist: query's target list (needed to look up pathkeys)
 * 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,
                       List *tlist,
                       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 = (WindowClause *) lfirst(l);
        List       *window_pathkeys;

        window_pathkeys = make_pathkeys_for_window(root,
                                                   wc,
                                                   tlist);

        /* Sort if necessary */
        if (!pathkeys_contained_in(window_pathkeys, path->pathkeys))
        {
            path = (Path *) create_sort_path(root, window_rel,
                                             path,
                                             window_pathkeys,
                                             -1.0);
        }

        if (lnext(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,
                                  window_pathkeys);
    }

    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)
{
    Query      *parse = root->parse;
    Path       *cheapest_input_path = input_rel->cheapest_total_path;
    RelOptInfo *distinct_rel;
    double      numDistinctRows;
    bool        allow_hash;
    Path       *path;
    ListCell   *lc;

    /* 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;

    /* 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);
    }

    /*
     * 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 several 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, or if it looks like the hashtable will exceed
     * work_mem.
     *
     * 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
    {
        Size        hashentrysize;

        /* Estimate per-hash-entry space at tuple width... */
        hashentrysize = MAXALIGN(cheapest_input_path->pathtarget->width) +
            MAXALIGN(SizeofMinimalTupleHeader);
        /* plus the per-hash-entry overhead */
        hashentrysize += hash_agg_entry_size(0);

        /* Allow hashing only if hashtable is predicted to fit in work_mem */
        allow_hash = (hashentrysize * numDistinctRows <= work_mem * 1024L);
    }

    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));
    }

    /* Give a helpful error if we failed to find any implementation */
    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);

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

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

    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 path we need consider is an explicit 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
 */
static RelOptInfo *
create_ordered_paths(PlannerInfo *root,
                     RelOptInfo *input_rel,
                     PathTarget *target,
                     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 &&
        is_parallel_safe(root, (Node *) target->exprs))
        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       *path = (Path *) lfirst(lc);
        bool        is_sorted;

        is_sorted = pathkeys_contained_in(root->sort_pathkeys,
                                          path->pathkeys);
        if (path == cheapest_input_path || is_sorted)
        {
            if (!is_sorted)
            {
                /* An explicit sort here can take advantage of LIMIT */
                path = (Path *) create_sort_path(root,
                                                 ordered_rel,
                                                 path,
                                                 root->sort_pathkeys,
                                                 limit_tuples);
            }

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

            add_path(ordered_rel, 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,
                                             -1.0);

            total_groups = cheapest_partial_path->rows *
                cheapest_partial_path->parallel_workers;
            path = (Path *)
                create_gather_merge_path(root, ordered_rel,
                                         path,
                                         target, 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);
        }
    }

    /*
     * 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);

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

    /*
     * 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.
 * We get the HAVING clause out of *root.
 */
static PathTarget *
make_partial_grouping_target(PlannerInfo *root, PathTarget *grouping_target)
{
    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 (parse->havingQual)
        non_group_cols = lappend(non_group_cols, parse->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 = (TargetEntry *) lfirst(l);
        TargetEntry *orig_tle;

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

        Assert(orig_tlist_item != NULL);
        orig_tle = (TargetEntry *) lfirst(orig_tlist_item);
        orig_tlist_item = lnext(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       *result;
    List       *actives;
    ListCell   *lc;

    /* First, make a list of the active windows */
    actives = NIL;
    foreach(lc, root->parse->windowClause)
    {
        WindowClause *wc = (WindowClause *) lfirst(lc);

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

    /*
     * Now, ensure that windows with identical partitioning/ordering clauses
     * are adjacent in the list.  This is required by the SQL standard, which
     * says that only one sort is to be used for such windows, even if they
     * are otherwise distinct (eg, different names or framing clauses).
     *
     * There is room to be much smarter here, for example detecting whether
     * one window's sort keys are a prefix of another's (so that sorting for
     * the latter would do for the former), or putting windows first that
     * match a sort order available for the underlying query.  For the moment
     * we are content with meeting the spec.
     */
    result = NIL;
    while (actives != NIL)
    {
        WindowClause *wc = (WindowClause *) linitial(actives);
        ListCell   *prev;
        ListCell   *next;

        /* Move wc from actives to result */
        actives = list_delete_first(actives);
        result = lappend(result, wc);

        /* Now move any matching windows from actives to result */
        prev = NULL;
        for (lc = list_head(actives); lc; lc = next)
        {
            WindowClause *wc2 = (WindowClause *) lfirst(lc);

            next = lnext(lc);
            /* framing options are NOT to be compared here! */
            if (equal(wc->partitionClause, wc2->partitionClause) &&
                equal(wc->orderClause, wc2->orderClause))
            {
                actives = list_delete_cell(actives, lc, prev);
                result = lappend(result, wc2);
            }
            else
                prev = lc;
        }
    }

    return result;
}

/*
 * 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 = (WindowClause *) lfirst(lc);
        ListCell   *lc2;

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

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

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

    /* Add in sortgroupref numbers of GROUP BY clauses, too */
    foreach(lc, parse->groupClause)
    {
        SortGroupClause *grpcl = (SortGroupClause *) lfirst(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.
 *
 * Caution: if you change this, see createplan.c's get_column_info_for_window!
 */
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(list_copy(wc->partitionClause),
                                     list_copy(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 n