allpaths.c

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/*-------------------------------------------------------------------------
 *
 * allpaths.c
 *    Routines to find possible search paths for processing a query
 *
 * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/optimizer/path/allpaths.c
 *
 *-------------------------------------------------------------------------
 */

#include "postgres.h"

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

#include "access/sysattr.h"
#include "access/tsmapi.h"
#include "catalog/pg_class.h"
#include "catalog/pg_operator.h"
#include "catalog/pg_proc.h"
#include "foreign/fdwapi.h"
#include "miscadmin.h"
#include "nodes/makefuncs.h"
#include "nodes/nodeFuncs.h"
#ifdef OPTIMIZER_DEBUG
#include "nodes/print.h"
#endif
#include "optimizer/appendinfo.h"
#include "optimizer/clauses.h"
#include "optimizer/cost.h"
#include "optimizer/geqo.h"
#include "optimizer/inherit.h"
#include "optimizer/optimizer.h"
#include "optimizer/pathnode.h"
#include "optimizer/paths.h"
#include "optimizer/plancat.h"
#include "optimizer/planner.h"
#include "optimizer/restrictinfo.h"
#include "optimizer/tlist.h"
#include "parser/parse_clause.h"
#include "parser/parsetree.h"
#include "partitioning/partbounds.h"
#include "partitioning/partprune.h"
#include "rewrite/rewriteManip.h"
#include "utils/lsyscache.h"


/* results of subquery_is_pushdown_safe */
typedef struct pushdown_safety_info
{
    bool       *unsafeColumns;  /* which output columns are unsafe to use */
    bool        unsafeVolatile; /* don't push down volatile quals */
    bool        unsafeLeaky;    /* don't push down leaky quals */
} pushdown_safety_info;

/* These parameters are set by GUC */
bool        enable_geqo = false;    /* just in case GUC doesn't set it */
int         geqo_threshold;
int         min_parallel_table_scan_size;
int         min_parallel_index_scan_size;

/* Hook for plugins to get control in set_rel_pathlist() */
set_rel_pathlist_hook_type set_rel_pathlist_hook = NULL;

/* Hook for plugins to replace standard_join_search() */
join_search_hook_type join_search_hook = NULL;


static void set_base_rel_consider_startup(PlannerInfo *root);
static void set_base_rel_sizes(PlannerInfo *root);
static void set_base_rel_pathlists(PlannerInfo *root);
static void set_rel_size(PlannerInfo *root, RelOptInfo *rel,
                         Index rti, RangeTblEntry *rte);
static void set_rel_pathlist(PlannerInfo *root, RelOptInfo *rel,
                             Index rti, RangeTblEntry *rte);
static void set_plain_rel_size(PlannerInfo *root, RelOptInfo *rel,
                               RangeTblEntry *rte);
static void create_plain_partial_paths(PlannerInfo *root, RelOptInfo *rel);
static void set_rel_consider_parallel(PlannerInfo *root, RelOptInfo *rel,
                                      RangeTblEntry *rte);
static void set_plain_rel_pathlist(PlannerInfo *root, RelOptInfo *rel,
                                   RangeTblEntry *rte);
static void set_tablesample_rel_size(PlannerInfo *root, RelOptInfo *rel,
                                     RangeTblEntry *rte);
static void set_tablesample_rel_pathlist(PlannerInfo *root, RelOptInfo *rel,
                                         RangeTblEntry *rte);
static void set_foreign_size(PlannerInfo *root, RelOptInfo *rel,
                             RangeTblEntry *rte);
static void set_foreign_pathlist(PlannerInfo *root, RelOptInfo *rel,
                                 RangeTblEntry *rte);
static void set_append_rel_size(PlannerInfo *root, RelOptInfo *rel,
                                Index rti, RangeTblEntry *rte);
static void set_append_rel_pathlist(PlannerInfo *root, RelOptInfo *rel,
                                    Index rti, RangeTblEntry *rte);
static void generate_orderedappend_paths(PlannerInfo *root, RelOptInfo *rel,
                                         List *live_childrels,
                                         List *all_child_pathkeys);
static Path *get_cheapest_parameterized_child_path(PlannerInfo *root,
                                                   RelOptInfo *rel,
                                                   Relids required_outer);
static void accumulate_append_subpath(Path *path,
                                      List **subpaths,
                                      List **special_subpaths);
static Path *get_singleton_append_subpath(Path *path);
static void set_dummy_rel_pathlist(RelOptInfo *rel);
static void set_subquery_pathlist(PlannerInfo *root, RelOptInfo *rel,
                                  Index rti, RangeTblEntry *rte);
static void set_function_pathlist(PlannerInfo *root, RelOptInfo *rel,
                                  RangeTblEntry *rte);
static void set_values_pathlist(PlannerInfo *root, RelOptInfo *rel,
                                RangeTblEntry *rte);
static void set_tablefunc_pathlist(PlannerInfo *root, RelOptInfo *rel,
                                   RangeTblEntry *rte);
static void set_cte_pathlist(PlannerInfo *root, RelOptInfo *rel,
                             RangeTblEntry *rte);
static void set_namedtuplestore_pathlist(PlannerInfo *root, RelOptInfo *rel,
                                         RangeTblEntry *rte);
static void set_result_pathlist(PlannerInfo *root, RelOptInfo *rel,
                                RangeTblEntry *rte);
static void set_worktable_pathlist(PlannerInfo *root, RelOptInfo *rel,
                                   RangeTblEntry *rte);
static RelOptInfo *make_rel_from_joinlist(PlannerInfo *root, List *joinlist);
static bool subquery_is_pushdown_safe(Query *subquery, Query *topquery,
                                      pushdown_safety_info *safetyInfo);
static bool recurse_pushdown_safe(Node *setOp, Query *topquery,
                                  pushdown_safety_info *safetyInfo);
static void check_output_expressions(Query *subquery,
                                     pushdown_safety_info *safetyInfo);
static void compare_tlist_datatypes(List *tlist, List *colTypes,
                                    pushdown_safety_info *safetyInfo);
static bool targetIsInAllPartitionLists(TargetEntry *tle, Query *query);
static bool qual_is_pushdown_safe(Query *subquery, Index rti, Node *qual,
                                  pushdown_safety_info *safetyInfo);
static void subquery_push_qual(Query *subquery,
                               RangeTblEntry *rte, Index rti, Node *qual);
static void recurse_push_qual(Node *setOp, Query *topquery,
                              RangeTblEntry *rte, Index rti, Node *qual);
static void remove_unused_subquery_outputs(Query *subquery, RelOptInfo *rel);


/*
 * make_one_rel
 *    Finds all possible access paths for executing a query, returning a
 *    single rel that represents the join of all base rels in the query.
 */
RelOptInfo *
make_one_rel(PlannerInfo *root, List *joinlist)
{
    RelOptInfo *rel;
    Index       rti;
    double      total_pages;

    /*
     * Construct the all_baserels Relids set.
     */
    root->all_baserels = NULL;
    for (rti = 1; rti < root->simple_rel_array_size; rti++)
    {
        RelOptInfo *brel = root->simple_rel_array[rti];

        /* there may be empty slots corresponding to non-baserel RTEs */
        if (brel == NULL)
            continue;

        Assert(brel->relid == rti); /* sanity check on array */

        /* ignore RTEs that are "other rels" */
        if (brel->reloptkind != RELOPT_BASEREL)
            continue;

        root->all_baserels = bms_add_member(root->all_baserels, brel->relid);
    }

    /* Mark base rels as to whether we care about fast-start plans */
    set_base_rel_consider_startup(root);

    /*
     * Compute size estimates and consider_parallel flags for each base rel.
     */
    set_base_rel_sizes(root);

    /*
     * We should now have size estimates for every actual table involved in
     * the query, and we also know which if any have been deleted from the
     * query by join removal, pruned by partition pruning, or eliminated by
     * constraint exclusion.  So we can now compute total_table_pages.
     *
     * Note that appendrels are not double-counted here, even though we don't
     * bother to distinguish RelOptInfos for appendrel parents, because the
     * parents will have pages = 0.
     *
     * XXX if a table is self-joined, we will count it once per appearance,
     * which perhaps is the wrong thing ... but that's not completely clear,
     * and detecting self-joins here is difficult, so ignore it for now.
     */
    total_pages = 0;
    for (rti = 1; rti < root->simple_rel_array_size; rti++)
    {
        RelOptInfo *brel = root->simple_rel_array[rti];

        if (brel == NULL)
            continue;

        Assert(brel->relid == rti); /* sanity check on array */

        if (IS_DUMMY_REL(brel))
            continue;

        if (IS_SIMPLE_REL(brel))
            total_pages += (double) brel->pages;
    }
    root->total_table_pages = total_pages;

    /*
     * Generate access paths for each base rel.
     */
    set_base_rel_pathlists(root);

    /*
     * Generate access paths for the entire join tree.
     */
    rel = make_rel_from_joinlist(root, joinlist);

    /*
     * The result should join all and only the query's base rels.
     */
    Assert(bms_equal(rel->relids, root->all_baserels));

    return rel;
}

/*
 * set_base_rel_consider_startup
 *    Set the consider_[param_]startup flags for each base-relation entry.
 *
 * For the moment, we only deal with consider_param_startup here; because the
 * logic for consider_startup is pretty trivial and is the same for every base
 * relation, we just let build_simple_rel() initialize that flag correctly to
 * start with.  If that logic ever gets more complicated it would probably
 * be better to move it here.
 */
static void
set_base_rel_consider_startup(PlannerInfo *root)
{
    /*
     * Since parameterized paths can only be used on the inside of a nestloop
     * join plan, there is usually little value in considering fast-start
     * plans for them.  However, for relations that are on the RHS of a SEMI
     * or ANTI join, a fast-start plan can be useful because we're only going
     * to care about fetching one tuple anyway.
     *
     * To minimize growth of planning time, we currently restrict this to
     * cases where the RHS is a single base relation, not a join; there is no
     * provision for consider_param_startup to get set at all on joinrels.
     * Also we don't worry about appendrels.  costsize.c's costing rules for
     * nestloop semi/antijoins don't consider such cases either.
     */
    ListCell   *lc;

    foreach(lc, root->join_info_list)
    {
        SpecialJoinInfo *sjinfo = (SpecialJoinInfo *) lfirst(lc);
        int         varno;

        if ((sjinfo->jointype == JOIN_SEMI || sjinfo->jointype == JOIN_ANTI) &&
            bms_get_singleton_member(sjinfo->syn_righthand, &varno))
        {
            RelOptInfo *rel = find_base_rel(root, varno);

            rel->consider_param_startup = true;
        }
    }
}

/*
 * set_base_rel_sizes
 *    Set the size estimates (rows and widths) for each base-relation entry.
 *    Also determine whether to consider parallel paths for base relations.
 *
 * We do this in a separate pass over the base rels so that rowcount
 * estimates are available for parameterized path generation, and also so
 * that each rel's consider_parallel flag is set correctly before we begin to
 * generate paths.
 */
static void
set_base_rel_sizes(PlannerInfo *root)
{
    Index       rti;

    for (rti = 1; rti < root->simple_rel_array_size; rti++)
    {
        RelOptInfo *rel = root->simple_rel_array[rti];
        RangeTblEntry *rte;

        /* there may be empty slots corresponding to non-baserel RTEs */
        if (rel == NULL)
            continue;

        Assert(rel->relid == rti);  /* sanity check on array */

        /* ignore RTEs that are "other rels" */
        if (rel->reloptkind != RELOPT_BASEREL)
            continue;

        rte = root->simple_rte_array[rti];

        /*
         * If parallelism is allowable for this query in general, see whether
         * it's allowable for this rel in particular.  We have to do this
         * before set_rel_size(), because (a) if this rel is an inheritance
         * parent, set_append_rel_size() will use and perhaps change the rel's
         * consider_parallel flag, and (b) for some RTE types, set_rel_size()
         * goes ahead and makes paths immediately.
         */
        if (root->glob->parallelModeOK)
            set_rel_consider_parallel(root, rel, rte);

        set_rel_size(root, rel, rti, rte);
    }
}

/*
 * set_base_rel_pathlists
 *    Finds all paths available for scanning each base-relation entry.
 *    Sequential scan and any available indices are considered.
 *    Each useful path is attached to its relation's 'pathlist' field.
 */
static void
set_base_rel_pathlists(PlannerInfo *root)
{
    Index       rti;

    for (rti = 1; rti < root->simple_rel_array_size; rti++)
    {
        RelOptInfo *rel = root->simple_rel_array[rti];

        /* there may be empty slots corresponding to non-baserel RTEs */
        if (rel == NULL)
            continue;

        Assert(rel->relid == rti);  /* sanity check on array */

        /* ignore RTEs that are "other rels" */
        if (rel->reloptkind != RELOPT_BASEREL)
            continue;

        set_rel_pathlist(root, rel, rti, root->simple_rte_array[rti]);
    }
}

/*
 * set_rel_size
 *    Set size estimates for a base relation
 */
static void
set_rel_size(PlannerInfo *root, RelOptInfo *rel,
             Index rti, RangeTblEntry *rte)
{
    if (rel->reloptkind == RELOPT_BASEREL &&
        relation_excluded_by_constraints(root, rel, rte))
    {
        /*
         * We proved we don't need to scan the rel via constraint exclusion,
         * so set up a single dummy path for it.  Here we only check this for
         * regular baserels; if it's an otherrel, CE was already checked in
         * set_append_rel_size().
         *
         * In this case, we go ahead and set up the relation's path right away
         * instead of leaving it for set_rel_pathlist to do.  This is because
         * we don't have a convention for marking a rel as dummy except by
         * assigning a dummy path to it.
         */
        set_dummy_rel_pathlist(rel);
    }
    else if (rte->inh)
    {
        /* It's an "append relation", process accordingly */
        set_append_rel_size(root, rel, rti, rte);
    }
    else
    {
        switch (rel->rtekind)
        {
            case RTE_RELATION:
                if (rte->relkind == RELKIND_FOREIGN_TABLE)
                {
                    /* Foreign table */
                    set_foreign_size(root, rel, rte);
                }
                else if (rte->relkind == RELKIND_PARTITIONED_TABLE)
                {
                    /*
                     * We could get here if asked to scan a partitioned table
                     * with ONLY.  In that case we shouldn't scan any of the
                     * partitions, so mark it as a dummy rel.
                     */
                    set_dummy_rel_pathlist(rel);
                }
                else if (rte->tablesample != NULL)
                {
                    /* Sampled relation */
                    set_tablesample_rel_size(root, rel, rte);
                }
                else
                {
                    /* Plain relation */
                    set_plain_rel_size(root, rel, rte);
                }
                break;
            case RTE_SUBQUERY:

                /*
                 * Subqueries don't support making a choice between
                 * parameterized and unparameterized paths, so just go ahead
                 * and build their paths immediately.
                 */
                set_subquery_pathlist(root, rel, rti, rte);
                break;
            case RTE_FUNCTION:
                set_function_size_estimates(root, rel);
                break;
            case RTE_TABLEFUNC:
                set_tablefunc_size_estimates(root, rel);
                break;
            case RTE_VALUES:
                set_values_size_estimates(root, rel);
                break;
            case RTE_CTE:

                /*
                 * CTEs don't support making a choice between parameterized
                 * and unparameterized paths, so just go ahead and build their
                 * paths immediately.
                 */
                if (rte->self_reference)
                    set_worktable_pathlist(root, rel, rte);
                else
                    set_cte_pathlist(root, rel, rte);
                break;
            case RTE_NAMEDTUPLESTORE:
                /* Might as well just build the path immediately */
                set_namedtuplestore_pathlist(root, rel, rte);
                break;
            case RTE_RESULT:
                /* Might as well just build the path immediately */
                set_result_pathlist(root, rel, rte);
                break;
            default:
                elog(ERROR, "unexpected rtekind: %d", (int) rel->rtekind);
                break;
        }
    }

    /*
     * We insist that all non-dummy rels have a nonzero rowcount estimate.
     */
    Assert(rel->rows > 0 || IS_DUMMY_REL(rel));
}

/*
 * set_rel_pathlist
 *    Build access paths for a base relation
 */
static void
set_rel_pathlist(PlannerInfo *root, RelOptInfo *rel,
                 Index rti, RangeTblEntry *rte)
{
    if (IS_DUMMY_REL(rel))
    {
        /* We already proved the relation empty, so nothing more to do */
    }
    else if (rte->inh)
    {
        /* It's an "append relation", process accordingly */
        set_append_rel_pathlist(root, rel, rti, rte);
    }
    else
    {
        switch (rel->rtekind)
        {
            case RTE_RELATION:
                if (rte->relkind == RELKIND_FOREIGN_TABLE)
                {
                    /* Foreign table */
                    set_foreign_pathlist(root, rel, rte);
                }
                else if (rte->tablesample != NULL)
                {
                    /* Sampled relation */
                    set_tablesample_rel_pathlist(root, rel, rte);
                }
                else
                {
                    /* Plain relation */
                    set_plain_rel_pathlist(root, rel, rte);
                }
                break;
            case RTE_SUBQUERY:
                /* Subquery --- fully handled during set_rel_size */
                break;
            case RTE_FUNCTION:
                /* RangeFunction */
                set_function_pathlist(root, rel, rte);
                break;
            case RTE_TABLEFUNC:
                /* Table Function */
                set_tablefunc_pathlist(root, rel, rte);
                break;
            case RTE_VALUES:
                /* Values list */
                set_values_pathlist(root, rel, rte);
                break;
            case RTE_CTE:
                /* CTE reference --- fully handled during set_rel_size */
                break;
            case RTE_NAMEDTUPLESTORE:
                /* tuplestore reference --- fully handled during set_rel_size */
                break;
            case RTE_RESULT:
                /* simple Result --- fully handled during set_rel_size */
                break;
            default:
                elog(ERROR, "unexpected rtekind: %d", (int) rel->rtekind);
                break;
        }
    }

    /*
     * Allow a plugin to editorialize on the set of Paths for this base
     * relation.  It could add new paths (such as CustomPaths) by calling
     * add_path(), or add_partial_path() if parallel aware.  It could also
     * delete or modify paths added by the core code.
     */
    if (set_rel_pathlist_hook)
        (*set_rel_pathlist_hook) (root, rel, rti, rte);

    /*
     * If this is a baserel, we should normally consider gathering any partial
     * paths we may have created for it.  We have to do this after calling the
     * set_rel_pathlist_hook, else it cannot add partial paths to be included
     * here.
     *
     * However, if this is an inheritance child, skip it.  Otherwise, we could
     * end up with a very large number of gather nodes, each trying to grab
     * its own pool of workers.  Instead, we'll consider gathering partial
     * paths for the parent appendrel.
     *
     * Also, if this is the topmost scan/join rel (that is, the only baserel),
     * we postpone gathering until the final scan/join targetlist is available
     * (see grouping_planner).
     */
    if (rel->reloptkind == RELOPT_BASEREL &&
        bms_membership(root->all_baserels) != BMS_SINGLETON)
        generate_useful_gather_paths(root, rel, false);

    /* Now find the cheapest of the paths for this rel */
    set_cheapest(rel);

#ifdef OPTIMIZER_DEBUG
    debug_print_rel(root, rel);
#endif
}

/*
 * set_plain_rel_size
 *    Set size estimates for a plain relation (no subquery, no inheritance)
 */
static void
set_plain_rel_size(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte)
{
    /*
     * Test any partial indexes of rel for applicability.  We must do this
     * first since partial unique indexes can affect size estimates.
     */
    check_index_predicates(root, rel);

    /* Mark rel with estimated output rows, width, etc */
    set_baserel_size_estimates(root, rel);
}

/*
 * If this relation could possibly be scanned from within a worker, then set
 * its consider_parallel flag.
 */
static void
set_rel_consider_parallel(PlannerInfo *root, RelOptInfo *rel,
                          RangeTblEntry *rte)
{
    /*
     * The flag has previously been initialized to false, so we can just
     * return if it becomes clear that we can't safely set it.
     */
    Assert(!rel->consider_parallel);

    /* Don't call this if parallelism is disallowed for the entire query. */
    Assert(root->glob->parallelModeOK);

    /* This should only be called for baserels and appendrel children. */
    Assert(IS_SIMPLE_REL(rel));

    /* Assorted checks based on rtekind. */
    switch (rte->rtekind)
    {
        case RTE_RELATION:

            /*
             * Currently, parallel workers can't access the leader's temporary
             * tables.  We could possibly relax this if we wrote all of its
             * local buffers at the start of the query and made no changes
             * thereafter (maybe we could allow hint bit changes), and if we
             * taught the workers to read them.  Writing a large number of
             * temporary buffers could be expensive, though, and we don't have
             * the rest of the necessary infrastructure right now anyway.  So
             * for now, bail out if we see a temporary table.
             */
            if (get_rel_persistence(rte->relid) == RELPERSISTENCE_TEMP)
                return;

            /*
             * Table sampling can be pushed down to workers if the sample
             * function and its arguments are safe.
             */
            if (rte->tablesample != NULL)
            {
                char        proparallel = func_parallel(rte->tablesample->tsmhandler);

                if (proparallel != PROPARALLEL_SAFE)
                    return;
                if (!is_parallel_safe(root, (Node *) rte->tablesample->args))
                    return;
            }

            /*
             * Ask FDWs whether they can support performing a ForeignScan
             * within a worker.  Most often, the answer will be no.  For
             * example, if the nature of the FDW is such that it opens a TCP
             * connection with a remote server, each parallel worker would end
             * up with a separate connection, and these connections might not
             * be appropriately coordinated between workers and the leader.
             */
            if (rte->relkind == RELKIND_FOREIGN_TABLE)
            {
                Assert(rel->fdwroutine);
                if (!rel->fdwroutine->IsForeignScanParallelSafe)
                    return;
                if (!rel->fdwroutine->IsForeignScanParallelSafe(root, rel, rte))
                    return;
            }

            /*
             * There are additional considerations for appendrels, which we'll
             * deal with in set_append_rel_size and set_append_rel_pathlist.
             * For now, just set consider_parallel based on the rel's own
             * quals and targetlist.
             */
            break;

        case RTE_SUBQUERY:

            /*
             * There's no intrinsic problem with scanning a subquery-in-FROM
             * (as distinct from a SubPlan or InitPlan) in a parallel worker.
             * If the subquery doesn't happen to have any parallel-safe paths,
             * then flagging it as consider_parallel won't change anything,
             * but that's true for plain tables, too.  We must set
             * consider_parallel based on the rel's own quals and targetlist,
             * so that if a subquery path is parallel-safe but the quals and
             * projection we're sticking onto it are not, we correctly mark
             * the SubqueryScanPath as not parallel-safe.  (Note that
             * set_subquery_pathlist() might push some of these quals down
             * into the subquery itself, but that doesn't change anything.)
             *
             * We can't push sub-select containing LIMIT/OFFSET to workers as
             * there is no guarantee that the row order will be fully
             * deterministic, and applying LIMIT/OFFSET will lead to
             * inconsistent results at the top-level.  (In some cases, where
             * the result is ordered, we could relax this restriction.  But it
             * doesn't currently seem worth expending extra effort to do so.)
             */
            {
                Query      *subquery = castNode(Query, rte->subquery);

                if (limit_needed(subquery))
                    return;
            }
            break;

        case RTE_JOIN:
            /* Shouldn't happen; we're only considering baserels here. */
            Assert(false);
            return;

        case RTE_FUNCTION:
            /* Check for parallel-restricted functions. */
            if (!is_parallel_safe(root, (Node *) rte->functions))
                return;
            break;

        case RTE_TABLEFUNC:
            /* not parallel safe */
            return;

        case RTE_VALUES:
            /* Check for parallel-restricted functions. */
            if (!is_parallel_safe(root, (Node *) rte->values_lists))
                return;
            break;

        case RTE_CTE:

            /*
             * CTE tuplestores aren't shared among parallel workers, so we
             * force all CTE scans to happen in the leader.  Also, populating
             * the CTE would require executing a subplan that's not available
             * in the worker, might be parallel-restricted, and must get
             * executed only once.
             */
            return;

        case RTE_NAMEDTUPLESTORE:

            /*
             * tuplestore cannot be shared, at least without more
             * infrastructure to support that.
             */
            return;

        case RTE_RESULT:
            /* RESULT RTEs, in themselves, are no problem. */
            break;
    }

    /*
     * If there's anything in baserestrictinfo that's parallel-restricted, we
     * give up on parallelizing access to this relation.  We could consider
     * instead postponing application of the restricted quals until we're
     * above all the parallelism in the plan tree, but it's not clear that
     * that would be a win in very many cases, and it might be tricky to make
     * outer join clauses work correctly.  It would likely break equivalence
     * classes, too.
     */
    if (!is_parallel_safe(root, (Node *) rel->baserestrictinfo))
        return;

    /*
     * Likewise, if the relation's outputs are not parallel-safe, give up.
     * (Usually, they're just Vars, but sometimes they're not.)
     */
    if (!is_parallel_safe(root, (Node *) rel->reltarget->exprs))
        return;

    /* We have a winner. */
    rel->consider_parallel = true;
}

/*
 * set_plain_rel_pathlist
 *    Build access paths for a plain relation (no subquery, no inheritance)
 */
static void
set_plain_rel_pathlist(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte)
{
    Relids      required_outer;

    /*
     * We don't support pushing join clauses into the quals of a seqscan, but
     * it could still have required parameterization due to LATERAL refs in
     * its tlist.
     */
    required_outer = rel->lateral_relids;

    /* Consider sequential scan */
    add_path(rel, create_seqscan_path(root, rel, required_outer, 0));

    /* If appropriate, consider parallel sequential scan */
    if (rel->consider_parallel && required_outer == NULL)
        create_plain_partial_paths(root, rel);

    /* Consider index scans */
    create_index_paths(root, rel);

    /* Consider TID scans */
    create_tidscan_paths(root, rel);
}

/*
 * create_plain_partial_paths
 *    Build partial access paths for parallel scan of a plain relation
 */
static void
create_plain_partial_paths(PlannerInfo *root, RelOptInfo *rel)
{
    int         parallel_workers;

    parallel_workers = compute_parallel_worker(rel, rel->pages, -1,
                                               max_parallel_workers_per_gather);

    /* If any limit was set to zero, the user doesn't want a parallel scan. */
    if (parallel_workers <= 0)
        return;

    /* Add an unordered partial path based on a parallel sequential scan. */
    add_partial_path(rel, create_seqscan_path(root, rel, NULL, parallel_workers));
}

/*
 * set_tablesample_rel_size
 *    Set size estimates for a sampled relation
 */
static void
set_tablesample_rel_size(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte)
{
    TableSampleClause *tsc = rte->tablesample;
    TsmRoutine *tsm;
    BlockNumber pages;
    double      tuples;

    /*
     * Test any partial indexes of rel for applicability.  We must do this
     * first since partial unique indexes can affect size estimates.
     */
    check_index_predicates(root, rel);

    /*
     * Call the sampling method's estimation function to estimate the number
     * of pages it will read and the number of tuples it will return.  (Note:
     * we assume the function returns sane values.)
     */
    tsm = GetTsmRoutine(tsc->tsmhandler);
    tsm->SampleScanGetSampleSize(root, rel, tsc->args,
                                 &pages, &tuples);

    /*
     * For the moment, because we will only consider a SampleScan path for the
     * rel, it's okay to just overwrite the pages and tuples estimates for the
     * whole relation.  If we ever consider multiple path types for sampled
     * rels, we'll need more complication.
     */
    rel->pages = pages;
    rel->tuples = tuples;

    /* Mark rel with estimated output rows, width, etc */
    set_baserel_size_estimates(root, rel);
}

/*
 * set_tablesample_rel_pathlist
 *    Build access paths for a sampled relation
 */
static void
set_tablesample_rel_pathlist(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte)
{
    Relids      required_outer;
    Path       *path;

    /*
     * We don't support pushing join clauses into the quals of a samplescan,
     * but it could still have required parameterization due to LATERAL refs
     * in its tlist or TABLESAMPLE arguments.
     */
    required_outer = rel->lateral_relids;

    /* Consider sampled scan */
    path = create_samplescan_path(root, rel, required_outer);

    /*
     * If the sampling method does not support repeatable scans, we must avoid
     * plans that would scan the rel multiple times.  Ideally, we'd simply
     * avoid putting the rel on the inside of a nestloop join; but adding such
     * a consideration to the planner seems like a great deal of complication
     * to support an uncommon usage of second-rate sampling methods.  Instead,
     * if there is a risk that the query might perform an unsafe join, just
     * wrap the SampleScan in a Materialize node.  We can check for joins by
     * counting the membership of all_baserels (note that this correctly
     * counts inheritance trees as single rels).  If we're inside a subquery,
     * we can't easily check whether a join might occur in the outer query, so
     * just assume one is possible.
     *
     * GetTsmRoutine is relatively expensive compared to the other tests here,
     * so check repeatable_across_scans last, even though that's a bit odd.
     */
    if ((root->query_level > 1 ||
         bms_membership(root->all_baserels) != BMS_SINGLETON) &&
        !(GetTsmRoutine(rte->tablesample->tsmhandler)->repeatable_across_scans))
    {
        path = (Path *) create_material_path(rel, path);
    }

    add_path(rel, path);

    /* For the moment, at least, there are no other paths to consider */
}

/*
 * set_foreign_size
 *      Set size estimates for a foreign table RTE
 */
static void
set_foreign_size(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte)
{
    /* Mark rel with estimated output rows, width, etc */
    set_foreign_size_estimates(root, rel);

    /* Let FDW adjust the size estimates, if it can */
    rel->fdwroutine->GetForeignRelSize(root, rel, rte->relid);

    /* ... but do not let it set the rows estimate to zero */
    rel->rows = clamp_row_est(rel->rows);

    /*
     * Also, make sure rel->tuples is not insane relative to rel->rows.
     * Notably, this ensures sanity if pg_class.reltuples contains -1 and the
     * FDW doesn't do anything to replace that.
     */
    rel->tuples = Max(rel->tuples, rel->rows);
}

/*
 * set_foreign_pathlist
 *      Build access paths for a foreign table RTE
 */
static void
set_foreign_pathlist(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte)
{
    /* Call the FDW's GetForeignPaths function to generate path(s) */
    rel->fdwroutine->GetForeignPaths(root, rel, rte->relid);
}

/*
 * set_append_rel_size
 *    Set size estimates for a simple "append relation"
 *
 * The passed-in rel and RTE represent the entire append relation.  The
 * relation's contents are computed by appending together the output of the
 * individual member relations.  Note that in the non-partitioned inheritance
 * case, the first member relation is actually the same table as is mentioned
 * in the parent RTE ... but it has a different RTE and RelOptInfo.  This is
 * a good thing because their outputs are not the same size.
 */
static void
set_append_rel_size(PlannerInfo *root, RelOptInfo *rel,
                    Index rti, RangeTblEntry *rte)
{
    int         parentRTindex = rti;
    bool        has_live_children;
    double      parent_rows;
    double      parent_size;
    double     *parent_attrsizes;
    int         nattrs;
    ListCell   *l;

    /* Guard against stack overflow due to overly deep inheritance tree. */
    check_stack_depth();

    Assert(IS_SIMPLE_REL(rel));

    /*
     * If this is a partitioned baserel, set the consider_partitionwise_join
     * flag; currently, we only consider partitionwise joins with the baserel
     * if its targetlist doesn't contain a whole-row Var.
     */
    if (enable_partitionwise_join &&
        rel->reloptkind == RELOPT_BASEREL &&
        rte->relkind == RELKIND_PARTITIONED_TABLE &&
        rel->attr_needed[InvalidAttrNumber - rel->min_attr] == NULL)
        rel->consider_partitionwise_join = true;

    /*
     * Initialize to compute size estimates for whole append relation.
     *
     * We handle width estimates by weighting the widths of different child
     * rels proportionally to their number of rows.  This is sensible because
     * the use of width estimates is mainly to compute the total relation
     * "footprint" if we have to sort or hash it.  To do this, we sum the
     * total equivalent size (in "double" arithmetic) and then divide by the
     * total rowcount estimate.  This is done separately for the total rel
     * width and each attribute.
     *
     * Note: if you consider changing this logic, beware that child rels could
     * have zero rows and/or width, if they were excluded by constraints.
     */
    has_live_children = false;
    parent_rows = 0;
    parent_size = 0;
    nattrs = rel->max_attr - rel->min_attr + 1;
    parent_attrsizes = (double *) palloc0(nattrs * sizeof(double));

    foreach(l, root->append_rel_list)
    {
        AppendRelInfo *appinfo = (AppendRelInfo *) lfirst(l);
        int         childRTindex;
        RangeTblEntry *childRTE;
        RelOptInfo *childrel;
        ListCell   *parentvars;
        ListCell   *childvars;

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

        childRTindex = appinfo->child_relid;
        childRTE = root->simple_rte_array[childRTindex];

        /*
         * The child rel's RelOptInfo was already created during
         * add_other_rels_to_query.
         */
        childrel = find_base_rel(root, childRTindex);
        Assert(childrel->reloptkind == RELOPT_OTHER_MEMBER_REL);

        /* We may have already proven the child to be dummy. */
        if (IS_DUMMY_REL(childrel))
            continue;

        /*
         * We have to copy the parent's targetlist and quals to the child,
         * with appropriate substitution of variables.  However, the
         * baserestrictinfo quals were already copied/substituted when the
         * child RelOptInfo was built.  So we don't need any additional setup
         * before applying constraint exclusion.
         */
        if (relation_excluded_by_constraints(root, childrel, childRTE))
        {
            /*
             * This child need not be scanned, so we can omit it from the
             * appendrel.
             */
            set_dummy_rel_pathlist(childrel);
            continue;
        }

        /*
         * Constraint exclusion failed, so copy the parent's join quals and
         * targetlist to the child, with appropriate variable substitutions.
         *
         * NB: the resulting childrel->reltarget->exprs may contain arbitrary
         * expressions, which otherwise would not occur in a rel's targetlist.
         * Code that might be looking at an appendrel child must cope with
         * such.  (Normally, a rel's targetlist would only include Vars and
         * PlaceHolderVars.)  XXX we do not bother to update the cost or width
         * fields of childrel->reltarget; not clear if that would be useful.
         */
        childrel->joininfo = (List *)
            adjust_appendrel_attrs(root,
                                   (Node *) rel->joininfo,
                                   1, &appinfo);
        childrel->reltarget->exprs = (List *)
            adjust_appendrel_attrs(root,
                                   (Node *) rel->reltarget->exprs,
                                   1, &appinfo);

        /*
         * We have to make child entries in the EquivalenceClass data
         * structures as well.  This is needed either if the parent
         * participates in some eclass joins (because we will want to consider
         * inner-indexscan joins on the individual children) or if the parent
         * has useful pathkeys (because we should try to build MergeAppend
         * paths that produce those sort orderings).
         */
        if (rel->has_eclass_joins || has_useful_pathkeys(root, rel))
            add_child_rel_equivalences(root, appinfo, rel, childrel);
        childrel->has_eclass_joins = rel->has_eclass_joins;

        /*
         * Note: we could compute appropriate attr_needed data for the child's
         * variables, by transforming the parent's attr_needed through the
         * translated_vars mapping.  However, currently there's no need
         * because attr_needed is only examined for base relations not
         * otherrels.  So we just leave the child's attr_needed empty.
         */

        /*
         * If we consider partitionwise joins with the parent rel, do the same
         * for partitioned child rels.
         *
         * Note: here we abuse the consider_partitionwise_join flag by setting
         * it for child rels that are not themselves partitioned.  We do so to
         * tell try_partitionwise_join() that the child rel is sufficiently
         * valid to be used as a per-partition input, even if it later gets
         * proven to be dummy.  (It's not usable until we've set up the
         * reltarget and EC entries, which we just did.)
         */
        if (rel->consider_partitionwise_join)
            childrel->consider_partitionwise_join = true;

        /*
         * If parallelism is allowable for this query in general, see whether
         * it's allowable for this childrel in particular.  But if we've
         * already decided the appendrel is not parallel-safe as a whole,
         * there's no point in considering parallelism for this child.  For
         * consistency, do this before calling set_rel_size() for the child.
         */
        if (root->glob->parallelModeOK && rel->consider_parallel)
            set_rel_consider_parallel(root, childrel, childRTE);

        /*
         * Compute the child's size.
         */
        set_rel_size(root, childrel, childRTindex, childRTE);

        /*
         * It is possible that constraint exclusion detected a contradiction
         * within a child subquery, even though we didn't prove one above. If
         * so, we can skip this child.
         */
        if (IS_DUMMY_REL(childrel))
            continue;

        /* We have at least one live child. */
        has_live_children = true;

        /*
         * If any live child is not parallel-safe, treat the whole appendrel
         * as not parallel-safe.  In future we might be able to generate plans
         * in which some children are farmed out to workers while others are
         * not; but we don't have that today, so it's a waste to consider
         * partial paths anywhere in the appendrel unless it's all safe.
         * (Child rels visited before this one will be unmarked in
         * set_append_rel_pathlist().)
         */
        if (!childrel->consider_parallel)
            rel->consider_parallel = false;

        /*
         * Accumulate size information from each live child.
         */
        Assert(childrel->rows > 0);

        parent_rows += childrel->rows;
        parent_size += childrel->reltarget->width * childrel->rows;

        /*
         * Accumulate per-column estimates too.  We need not do anything for
         * PlaceHolderVars in the parent list.  If child expression isn't a
         * Var, or we didn't record a width estimate for it, we have to fall
         * back on a datatype-based estimate.
         *
         * By construction, child's targetlist is 1-to-1 with parent's.
         */
        forboth(parentvars, rel->reltarget->exprs,
                childvars, childrel->reltarget->exprs)
        {
            Var        *parentvar = (Var *) lfirst(parentvars);
            Node       *childvar = (Node *) lfirst(childvars);

            if (IsA(parentvar, Var))
            {
                int         pndx = parentvar->varattno - rel->min_attr;
                int32       child_width = 0;

                if (IsA(childvar, Var) &&
                    ((Var *) childvar)->varno == childrel->relid)
                {
                    int         cndx = ((Var *) childvar)->varattno - childrel->min_attr;

                    child_width = childrel->attr_widths[cndx];
                }
                if (child_width <= 0)
                    child_width = get_typavgwidth(exprType(childvar),
                                                  exprTypmod(childvar));
                Assert(child_width > 0);
                parent_attrsizes[pndx] += child_width * childrel->rows;
            }
        }
    }

    if (has_live_children)
    {
        /*
         * Save the finished size estimates.
         */
        int         i;

        Assert(parent_rows > 0);
        rel->rows = parent_rows;
        rel->reltarget->width = rint(parent_size / parent_rows);
        for (i = 0; i < nattrs; i++)
            rel->attr_widths[i] = rint(parent_attrsizes[i] / parent_rows);

        /*
         * Set "raw tuples" count equal to "rows" for the appendrel; needed
         * because some places assume rel->tuples is valid for any baserel.
         */
        rel->tuples = parent_rows;

        /*
         * Note that we leave rel->pages as zero; this is important to avoid
         * double-counting the appendrel tree in total_table_pages.
         */
    }
    else
    {
        /*
         * All children were excluded by constraints, so mark the whole
         * appendrel dummy.  We must do this in this phase so that the rel's
         * dummy-ness is visible when we generate paths for other rels.
         */
        set_dummy_rel_pathlist(rel);
    }

    pfree(parent_attrsizes);
}

/*
 * set_append_rel_pathlist
 *    Build access paths for an "append relation"
 */
static void
set_append_rel_pathlist(PlannerInfo *root, RelOptInfo *rel,
                        Index rti, RangeTblEntry *rte)
{
    int         parentRTindex = rti;
    List       *live_childrels = NIL;
    ListCell   *l;

    /*
     * Generate access paths for each member relation, and remember the
     * non-dummy children.
     */
    foreach(l, root->append_rel_list)
    {
        AppendRelInfo *appinfo = (AppendRelInfo *) lfirst(l);
        int         childRTindex;
        RangeTblEntry *childRTE;
        RelOptInfo *childrel;

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

        /* Re-locate the child RTE and RelOptInfo */
        childRTindex = appinfo->child_relid;
        childRTE = root->simple_rte_array[childRTindex];
        childrel = root->simple_rel_array[childRTindex];

        /*
         * If set_append_rel_size() decided the parent appendrel was
         * parallel-unsafe at some point after visiting this child rel, we
         * need to propagate the unsafety marking down to the child, so that
         * we don't generate useless partial paths for it.
         */
        if (!rel->consider_parallel)
            childrel->consider_parallel = false;

        /*
         * Compute the child's access paths.
         */
        set_rel_pathlist(root, childrel, childRTindex, childRTE);

        /*
         * If child is dummy, ignore it.
         */
        if (IS_DUMMY_REL(childrel))
            continue;

        /*
         * Child is live, so add it to the live_childrels list for use below.
         */
        live_childrels = lappend(live_childrels, childrel);
    }

    /* Add paths to the append relation. */
    add_paths_to_append_rel(root, rel, live_childrels);
}


/*
 * add_paths_to_append_rel
 *      Generate paths for the given append relation given the set of non-dummy
 *      child rels.
 *
 * The function collects all parameterizations and orderings supported by the
 * non-dummy children. For every such parameterization or ordering, it creates
 * an append path collecting one path from each non-dummy child with given
 * parameterization or ordering. Similarly it collects partial paths from
 * non-dummy children to create partial append paths.
 */
void
add_paths_to_append_rel(PlannerInfo *root, RelOptInfo *rel,
                        List *live_childrels)
{
    List       *subpaths = NIL;
    bool        subpaths_valid = true;
    List       *partial_subpaths = NIL;
    List       *pa_partial_subpaths = NIL;
    List       *pa_nonpartial_subpaths = NIL;
    bool        partial_subpaths_valid = true;
    bool        pa_subpaths_valid;
    List       *all_child_pathkeys = NIL;
    List       *all_child_outers = NIL;
    ListCell   *l;
    double      partial_rows = -1;

    /* If appropriate, consider parallel append */
    pa_subpaths_valid = enable_parallel_append && rel->consider_parallel;

    /*
     * For every non-dummy child, remember the cheapest path.  Also, identify
     * all pathkeys (orderings) and parameterizations (required_outer sets)
     * available for the non-dummy member relations.
     */
    foreach(l, live_childrels)
    {
        RelOptInfo *childrel = lfirst(l);
        ListCell   *lcp;
        Path       *cheapest_partial_path = NULL;

        /*
         * If child has an unparameterized cheapest-total path, add that to
         * the unparameterized Append path we are constructing for the parent.
         * If not, there's no workable unparameterized path.
         *
         * With partitionwise aggregates, the child rel's pathlist may be
         * empty, so don't assume that a path exists here.
         */
        if (childrel->pathlist != NIL &&
            childrel->cheapest_total_path->param_info == NULL)
            accumulate_append_subpath(childrel->cheapest_total_path,
                                      &subpaths, NULL);
        else
            subpaths_valid = false;

        /* Same idea, but for a partial plan. */
        if (childrel->partial_pathlist != NIL)
        {
            cheapest_partial_path = linitial(childrel->partial_pathlist);
            accumulate_append_subpath(cheapest_partial_path,
                                      &partial_subpaths, NULL);
        }
        else
            partial_subpaths_valid = false;

        /*
         * Same idea, but for a parallel append mixing partial and non-partial
         * paths.
         */
        if (pa_subpaths_valid)
        {
            Path       *nppath = NULL;

            nppath =
                get_cheapest_parallel_safe_total_inner(childrel->pathlist);

            if (cheapest_partial_path == NULL && nppath == NULL)
            {
                /* Neither a partial nor a parallel-safe path?  Forget it. */
                pa_subpaths_valid = false;
            }
            else if (nppath == NULL ||
                     (cheapest_partial_path != NULL &&
                      cheapest_partial_path->total_cost < nppath->total_cost))
            {
                /* Partial path is cheaper or the only option. */
                Assert(cheapest_partial_path != NULL);
                accumulate_append_subpath(cheapest_partial_path,
                                          &pa_partial_subpaths,
                                          &pa_nonpartial_subpaths);
            }
            else
            {
                /*
                 * Either we've got only a non-partial path, or we think that
                 * a single backend can execute the best non-partial path
                 * faster than all the parallel backends working together can
                 * execute the best partial path.
                 *
                 * It might make sense to be more aggressive here.  Even if
                 * the best non-partial path is more expensive than the best
                 * partial path, it could still be better to choose the
                 * non-partial path if there are several such paths that can
                 * be given to different workers.  For now, we don't try to
                 * figure that out.
                 */
                accumulate_append_subpath(nppath,
                                          &pa_nonpartial_subpaths,
                                          NULL);
            }
        }

        /*
         * Collect lists of all the available path orderings and
         * parameterizations for all the children.  We use these as a
         * heuristic to indicate which sort orderings and parameterizations we
         * should build Append and MergeAppend paths for.
         */
        foreach(lcp, childrel->pathlist)
        {
            Path       *childpath = (Path *) lfirst(lcp);
            List       *childkeys = childpath->pathkeys;
            Relids      childouter = PATH_REQ_OUTER(childpath);

            /* Unsorted paths don't contribute to pathkey list */
            if (childkeys != NIL)
            {
                ListCell   *lpk;
                bool        found = false;

                /* Have we already seen this ordering? */
                foreach(lpk, all_child_pathkeys)
                {
                    List       *existing_pathkeys = (List *) lfirst(lpk);

                    if (compare_pathkeys(existing_pathkeys,
                                         childkeys) == PATHKEYS_EQUAL)
                    {
                        found = true;
                        break;
                    }
                }
                if (!found)
                {
                    /* No, so add it to all_child_pathkeys */
                    all_child_pathkeys = lappend(all_child_pathkeys,
                                                 childkeys);
                }
            }

            /* Unparameterized paths don't contribute to param-set list */
            if (childouter)
            {
                ListCell   *lco;
                bool        found = false;

                /* Have we already seen this param set? */
                foreach(lco, all_child_outers)
                {
                    Relids      existing_outers = (Relids) lfirst(lco);

                    if (bms_equal(existing_outers, childouter))
                    {
                        found = true;
                        break;
                    }
                }
                if (!found)
                {
                    /* No, so add it to all_child_outers */
                    all_child_outers = lappend(all_child_outers,
                                               childouter);
                }
            }
        }
    }

    /*
     * If we found unparameterized paths for all children, build an unordered,
     * unparameterized Append path for the rel.  (Note: this is correct even
     * if we have zero or one live subpath due to constraint exclusion.)
     */
    if (subpaths_valid)
        add_path(rel, (Path *) create_append_path(root, rel, subpaths, NIL,
                                                  NIL, NULL, 0, false,
                                                  -1));

    /*
     * Consider an append of unordered, unparameterized partial paths.  Make
     * it parallel-aware if possible.
     */
    if (partial_subpaths_valid && partial_subpaths != NIL)
    {
        AppendPath *appendpath;
        ListCell   *lc;
        int         parallel_workers = 0;

        /* Find the highest number of workers requested for any subpath. */
        foreach(lc, partial_subpaths)
        {
            Path       *path = lfirst(lc);

            parallel_workers = Max(parallel_workers, path->parallel_workers);
        }
        Assert(parallel_workers > 0);

        /*
         * If the use of parallel append is permitted, always request at least
         * log2(# of children) workers.  We assume it can be useful to have
         * extra workers in this case because they will be spread out across
         * the children.  The precise formula is just a guess, but we don't
         * want to end up with a radically different answer for a table with N
         * partitions vs. an unpartitioned table with the same data, so the
         * use of some kind of log-scaling here seems to make some sense.
         */
        if (enable_parallel_append)
        {
            parallel_workers = Max(parallel_workers,
                                   fls(list_length(live_childrels)));
            parallel_workers = Min(parallel_workers,
                                   max_parallel_workers_per_gather);
        }
        Assert(parallel_workers > 0);

        /* Generate a partial append path. */
        appendpath = create_append_path(root, rel, NIL, partial_subpaths,
                                        NIL, NULL, parallel_workers,
                                        enable_parallel_append,
                                        -1);

        /*
         * Make sure any subsequent partial paths use the same row count
         * estimate.
         */
        partial_rows = appendpath->path.rows;

        /* Add the path. */
        add_partial_path(rel, (Path *) appendpath);
    }

    /*
     * Consider a parallel-aware append using a mix of partial and non-partial
     * paths.  (This only makes sense if there's at least one child which has
     * a non-partial path that is substantially cheaper than any partial path;
     * otherwise, we should use the append path added in the previous step.)
     */
    if (pa_subpaths_valid && pa_nonpartial_subpaths != NIL)
    {
        AppendPath *appendpath;
        ListCell   *lc;
        int         parallel_workers = 0;

        /*
         * Find the highest number of workers requested for any partial
         * subpath.
         */
        foreach(lc, pa_partial_subpaths)
        {
            Path       *path = lfirst(lc);

            parallel_workers = Max(parallel_workers, path->parallel_workers);
        }

        /*
         * Same formula here as above.  It's even more important in this
         * instance because the non-partial paths won't contribute anything to
         * the planned number of parallel workers.
         */
        parallel_workers = Max(parallel_workers,
                               fls(list_length(live_childrels)));
        parallel_workers = Min(parallel_workers,
                               max_parallel_workers_per_gather);
        Assert(parallel_workers > 0);

        appendpath = create_append_path(root, rel, pa_nonpartial_subpaths,
                                        pa_partial_subpaths,
                                        NIL, NULL, parallel_workers, true,
                                        partial_rows);
        add_partial_path(rel, (Path *) appendpath);
    }

    /*
     * Also build unparameterized ordered append paths based on the collected
     * list of child pathkeys.
     */
    if (subpaths_valid)
        generate_orderedappend_paths(root, rel, live_childrels,
                                     all_child_pathkeys);

    /*
     * Build Append paths for each parameterization seen among the child rels.
     * (This may look pretty expensive, but in most cases of practical
     * interest, the child rels will expose mostly the same parameterizations,
     * so that not that many cases actually get considered here.)
     *
     * The Append node itself cannot enforce quals, so all qual checking must
     * be done in the child paths.  This means that to have a parameterized
     * Append path, we must have the exact same parameterization for each
     * child path; otherwise some children might be failing to check the
     * moved-down quals.  To make them match up, we can try to increase the
     * parameterization of lesser-parameterized paths.
     */
    foreach(l, all_child_outers)
    {
        Relids      required_outer = (Relids) lfirst(l);
        ListCell   *lcr;

        /* Select the child paths for an Append with this parameterization */
        subpaths = NIL;
        subpaths_valid = true;
        foreach(lcr, live_childrels)
        {
            RelOptInfo *childrel = (RelOptInfo *) lfirst(lcr);
            Path       *subpath;

            if (childrel->pathlist == NIL)
            {
                /* failed to make a suitable path for this child */
                subpaths_valid = false;
                break;
            }

            subpath = get_cheapest_parameterized_child_path(root,
                                                            childrel,
                                                            required_outer);
            if (subpath == NULL)
            {
                /* failed to make a suitable path for this child */
                subpaths_valid = false;
                break;
            }
            accumulate_append_subpath(subpath, &subpaths, NULL);
        }

        if (subpaths_valid)
            add_path(rel, (Path *)
                     create_append_path(root, rel, subpaths, NIL,
                                        NIL, required_outer, 0, false,
                                        -1));
    }

    /*
     * When there is only a single child relation, the Append path can inherit
     * any ordering available for the child rel's path, so that it's useful to
     * consider ordered partial paths.  Above we only considered the cheapest
     * partial path for each child, but let's also make paths using any
     * partial paths that have pathkeys.
     */
    if (list_length(live_childrels) == 1)
    {
        RelOptInfo *childrel = (RelOptInfo *) linitial(live_childrels);

        /* skip the cheapest partial path, since we already used that above */
        for_each_from(l, childrel->partial_pathlist, 1)
        {
            Path       *path = (Path *) lfirst(l);
            AppendPath *appendpath;

            /* skip paths with no pathkeys. */
            if (path->pathkeys == NIL)
                continue;

            appendpath = create_append_path(root, rel, NIL, list_make1(path),
                                            NIL, NULL,
                                            path->parallel_workers, true,
                                            partial_rows);
            add_partial_path(rel, (Path *) appendpath);
        }
    }
}

/*
 * generate_orderedappend_paths
 *      Generate ordered append paths for an append relation
 *
 * Usually we generate MergeAppend paths here, but there are some special
 * cases where we can generate simple Append paths, because the subpaths
 * can provide tuples in the required order already.
 *
 * We generate a path for each ordering (pathkey list) appearing in
 * all_child_pathkeys.
 *
 * We consider both cheapest-startup and cheapest-total cases, ie, for each
 * interesting ordering, collect all the cheapest startup subpaths and all the
 * cheapest total paths, and build a suitable path for each case.
 *
 * We don't currently generate any parameterized ordered paths here.  While
 * it would not take much more code here to do so, it's very unclear that it
 * is worth the planning cycles to investigate such paths: there's little
 * use for an ordered path on the inside of a nestloop.  In fact, it's likely
 * that the current coding of add_path would reject such paths out of hand,
 * because add_path gives no credit for sort ordering of parameterized paths,
 * and a parameterized MergeAppend is going to be more expensive than the
 * corresponding parameterized Append path.  If we ever try harder to support
 * parameterized mergejoin plans, it might be worth adding support for
 * parameterized paths here to feed such joins.  (See notes in
 * optimizer/README for why that might not ever happen, though.)
 */
static void
generate_orderedappend_paths(PlannerInfo *root, RelOptInfo *rel,
                             List *live_childrels,
                             List *all_child_pathkeys)
{
    ListCell   *lcp;
    List       *partition_pathkeys = NIL;
    List       *partition_pathkeys_desc = NIL;
    bool        partition_pathkeys_partial = true;
    bool        partition_pathkeys_desc_partial = true;

    /*
     * Some partitioned table setups may allow us to use an Append node
     * instead of a MergeAppend.  This is possible in cases such as RANGE
     * partitioned tables where it's guaranteed that an earlier partition must
     * contain rows which come earlier in the sort order.  To detect whether
     * this is relevant, build pathkey descriptions of the partition ordering,
     * for both forward and reverse scans.
     */
    if (rel->part_scheme != NULL && IS_SIMPLE_REL(rel) &&
        partitions_are_ordered(rel->boundinfo, rel->nparts))
    {
        partition_pathkeys = build_partition_pathkeys(root, rel,
                                                      ForwardScanDirection,
                                                      &partition_pathkeys_partial);

        partition_pathkeys_desc = build_partition_pathkeys(root, rel,
                                                           BackwardScanDirection,
                                                           &partition_pathkeys_desc_partial);

        /*
         * You might think we should truncate_useless_pathkeys here, but
         * allowing partition keys which are a subset of the query's pathkeys
         * can often be useful.  For example, consider a table partitioned by
         * RANGE (a, b), and a query with ORDER BY a, b, c.  If we have child
         * paths that can produce the a, b, c ordering (perhaps via indexes on
         * (a, b, c)) then it works to consider the appendrel output as
         * ordered by a, b, c.
         */
    }

    /* Now consider each interesting sort ordering */
    foreach(lcp, all_child_pathkeys)
    {
        List       *pathkeys = (List *) lfirst(lcp);
        List       *startup_subpaths = NIL;
        List       *total_subpaths = NIL;
        bool        startup_neq_total = false;
        ListCell   *lcr;
        bool        match_partition_order;
        bool        match_partition_order_desc;

        /*
         * Determine if this sort ordering matches any partition pathkeys we
         * have, for both ascending and descending partition order.  If the
         * partition pathkeys happen to be contained in pathkeys then it still
         * works, as described above, providing that the partition pathkeys
         * are complete and not just a prefix of the partition keys.  (In such
         * cases we'll be relying on the child paths to have sorted the
         * lower-order columns of the required pathkeys.)
         */
        match_partition_order =
            pathkeys_contained_in(pathkeys, partition_pathkeys) ||
            (!partition_pathkeys_partial &&
             pathkeys_contained_in(partition_pathkeys, pathkeys));

        match_partition_order_desc = !match_partition_order &&
            (pathkeys_contained_in(pathkeys, partition_pathkeys_desc) ||
             (!partition_pathkeys_desc_partial &&
              pathkeys_contained_in(partition_pathkeys_desc, pathkeys)));

        /* Select the child paths for this ordering... */
        foreach(lcr, live_childrels)
        {
            RelOptInfo *childrel = (RelOptInfo *) lfirst(lcr);
            Path       *cheapest_startup,
                       *cheapest_total;

            /* Locate the right paths, if they are available. */
            cheapest_startup =
                get_cheapest_path_for_pathkeys(childrel->pathlist,
                                               pathkeys,
                                               NULL,
                                               STARTUP_COST,
                                               false);
            cheapest_total =
                get_cheapest_path_for_pathkeys(childrel->pathlist,
                                               pathkeys,
                                               NULL,
                                               TOTAL_COST,
                                               false);

            /*
             * If we can't find any paths with the right order just use the
             * cheapest-total path; we'll have to sort it later.
             */
            if (cheapest_startup == NULL || cheapest_total == NULL)
            {
                cheapest_startup = cheapest_total =
                    childrel->cheapest_total_path;
                /* Assert we do have an unparameterized path for this child */
                Assert(cheapest_total->param_info == NULL);
            }

            /*
             * Notice whether we actually have different paths for the
             * "cheapest" and "total" cases; frequently there will be no point
             * in two create_merge_append_path() calls.
             */
            if (cheapest_startup != cheapest_total)
                startup_neq_total = true;

            /*
             * Collect the appropriate child paths.  The required logic varies
             * for the Append and MergeAppend cases.
             */
            if (match_partition_order)
            {
                /*
                 * We're going to make a plain Append path.  We don't need
                 * most of what accumulate_append_subpath would do, but we do
                 * want to cut out child Appends or MergeAppends if they have
                 * just a single subpath (and hence aren't doing anything
                 * useful).
                 */
                cheapest_startup = get_singleton_append_subpath(cheapest_startup);
                cheapest_total = get_singleton_append_subpath(cheapest_total);

                startup_subpaths = lappend(startup_subpaths, cheapest_startup);
                total_subpaths = lappend(total_subpaths, cheapest_total);
            }
            else if (match_partition_order_desc)
            {
                /*
                 * As above, but we need to reverse the order of the children,
                 * because nodeAppend.c doesn't know anything about reverse
                 * ordering and will scan the children in the order presented.
                 */
                cheapest_startup = get_singleton_append_subpath(cheapest_startup);
                cheapest_total = get_singleton_append_subpath(cheapest_total);

                startup_subpaths = lcons(cheapest_startup, startup_subpaths);
                total_subpaths = lcons(cheapest_total, total_subpaths);
            }
            else
            {
                /*
                 * Otherwise, rely on accumulate_append_subpath to collect the
                 * child paths for the MergeAppend.
                 */
                accumulate_append_subpath(cheapest_startup,
                                          &startup_subpaths, NULL);
                accumulate_append_subpath(cheapest_total,
                                          &total_subpaths, NULL);
            }
        }

        /* ... and build the Append or MergeAppend paths */
        if (match_partition_order || match_partition_order_desc)
        {
            /* We only need Append */
            add_path(rel, (Path *) create_append_path(root,
                                                      rel,
                                                      startup_subpaths,
                                                      NIL,
                                                      pathkeys,
                                                      NULL,
                                                      0,
                                                      false,
                                                      -1));
            if (startup_neq_total)
                add_path(rel, (Path *) create_append_path(root,
                                                          rel,
                                                          total_subpaths,
                                                          NIL,
                                                          pathkeys,
                                                          NULL,
                                                          0,
                                                          false,
                                                          -1));
        }
        else
        {
            /* We need MergeAppend */
            add_path(rel, (Path *) create_merge_append_path(root,
                                                            rel,
                                                            startup_subpaths,
                                                            pathkeys,
                                                            NULL));
            if (startup_neq_total)
                add_path(rel, (Path *) create_merge_append_path(root,
                                                                rel,
                                                                total_subpaths,
                                                                pathkeys,
                                                                NULL));
        }
    }
}

/*
 * get_cheapest_parameterized_child_path
 *      Get cheapest path for this relation that has exactly the requested
 *      parameterization.
 *
 * Returns NULL if unable to create such a path.
 */
static Path *
get_cheapest_parameterized_child_path(PlannerInfo *root, RelOptInfo *rel,
                                      Relids required_outer)
{
    Path       *cheapest;
    ListCell   *lc;

    /*
     * Look up the cheapest existing path with no more than the needed
     * parameterization.  If it has exactly the needed parameterization, we're
     * done.
     */
    cheapest = get_cheapest_path_for_pathkeys(rel->pathlist,
                                              NIL,
                                              required_outer,
                                              TOTAL_COST,
                                              false);
    Assert(cheapest != NULL);
    if (bms_equal(PATH_REQ_OUTER(cheapest), required_outer))
        return cheapest;

    /*
     * Otherwise, we can "reparameterize" an existing path to match the given
     * parameterization, which effectively means pushing down additional
     * joinquals to be checked within the path's scan.  However, some existing
     * paths might check the available joinquals already while others don't;
     * therefore, it's not clear which existing path will be cheapest after
     * reparameterization.  We have to go through them all and find out.
     */
    cheapest = NULL;
    foreach(lc, rel->pathlist)
    {
        Path       *path = (Path *) lfirst(lc);

        /* Can't use it if it needs more than requested parameterization */
        if (!bms_is_subset(PATH_REQ_OUTER(path), required_outer))
            continue;

        /*
         * Reparameterization can only increase the path's cost, so if it's
         * already more expensive than the current cheapest, forget it.
         */
        if (cheapest != NULL &&
            compare_path_costs(cheapest, path, TOTAL_COST) <= 0)
            continue;

        /* Reparameterize if needed, then recheck cost */
        if (!bms_equal(PATH_REQ_OUTER(path), required_outer))
        {
            path = reparameterize_path(root, path, required_outer, 1.0);
            if (path == NULL)
                continue;       /* failed to reparameterize this one */
            Assert(bms_equal(PATH_REQ_OUTER(path), required_outer));

            if (cheapest != NULL &&
                compare_path_costs(cheapest, path, TOTAL_COST) <= 0)
                continue;
        }

        /* We have a new best path */
        cheapest = path;
    }

    /* Return the best path, or NULL if we found no suitable candidate */
    return cheapest;
}

/*
 * accumulate_append_subpath
 *      Add a subpath to the list being built for an Append or MergeAppend.
 *
 * It's possible that the child is itself an Append or MergeAppend path, in
 * which case we can "cut out the middleman" and just add its child paths to
 * our own list.  (We don't try to do this earlier because we need to apply
 * both levels of transformation to the quals.)
 *
 * Note that if we omit a child MergeAppend in this way, we are effectively
 * omitting a sort step, which seems fine: if the parent is to be an Append,
 * its result would be unsorted anyway, while if the parent is to be a
 * MergeAppend, there's no point in a separate sort on a child.
 *
 * Normally, either path is a partial path and subpaths is a list of partial
 * paths, or else path is a non-partial plan and subpaths is a list of those.
 * However, if path is a parallel-aware Append, then we add its partial path
 * children to subpaths and the rest to special_subpaths.  If the latter is
 * NULL, we don't flatten the path at all (unless it contains only partial
 * paths).
 */
static void
accumulate_append_subpath(Path *path, List **subpaths, List **special_subpaths)
{
    if (IsA(path, AppendPath))
    {
        AppendPath *apath = (AppendPath *) path;

        if (!apath->path.parallel_aware || apath->first_partial_path == 0)
        {
            *subpaths = list_concat(*subpaths, apath->subpaths);
            return;
        }
        else if (special_subpaths != NULL)
        {
            List       *new_special_subpaths;

            /* Split Parallel Append into partial and non-partial subpaths */
            *subpaths = list_concat(*subpaths,
                                    list_copy_tail(apath->subpaths,
                                                   apath->first_partial_path));
            new_special_subpaths =
                list_truncate(list_copy(apath->subpaths),
                              apath->first_partial_path);
            *special_subpaths = list_concat(*special_subpaths,
                                            new_special_subpaths);
            return;
        }
    }
    else if (IsA(path, MergeAppendPath))
    {
        MergeAppendPath *mpath = (MergeAppendPath *) path;

        *subpaths = list_concat(*subpaths, mpath->subpaths);
        return;
    }

    *subpaths = lappend(*subpaths, path);
}

/*
 * get_singleton_append_subpath
 *      Returns the single subpath of an Append/MergeAppend, or just
 *      return 'path' if it's not a single sub-path Append/MergeAppend.
 *
 * Note: 'path' must not be a parallel-aware path.
 */
static Path *
get_singleton_append_subpath(Path *path)
{
    Assert(!path->parallel_aware);

    if (IsA(path, AppendPath))
    {
        AppendPath *apath = (AppendPath *) path;

        if (list_length(apath->subpaths) == 1)
            return (Path *) linitial(apath->subpaths);
    }
    else if (IsA(path, MergeAppendPath))
    {
        MergeAppendPath *mpath = (MergeAppendPath *) path;

        if (list_length(mpath->subpaths) == 1)
            return (Path *) linitial(mpath->subpaths);
    }

    return path;
}

/*
 * set_dummy_rel_pathlist
 *    Build a dummy path for a relation that's been excluded by constraints
 *
 * Rather than inventing a special "dummy" path type, we represent this as an
 * AppendPath with no members (see also IS_DUMMY_APPEND/IS_DUMMY_REL macros).
 *
 * (See also mark_dummy_rel, which does basically the same thing, but is
 * typically used to change a rel into dummy state after we already made
 * paths for it.)
 */
static void
set_dummy_rel_pathlist(RelOptInfo *rel)
{
    /* Set dummy size estimates --- we leave attr_widths[] as zeroes */
    rel->rows = 0;
    rel->reltarget->width = 0;

    /* Discard any pre-existing paths; no further need for them */
    rel->pathlist = NIL;
    rel->partial_pathlist = NIL;

    /* Set up the dummy path */
    add_path(rel, (Path *) create_append_path(NULL, rel, NIL, NIL,
                                              NIL, rel->lateral_relids,
                                              0, false, -1));

    /*
     * We set the cheapest-path fields immediately, just in case they were
     * pointing at some discarded path.  This is redundant when we're called
     * from set_rel_size(), but not when called from elsewhere, and doing it
     * twice is harmless anyway.
     */
    set_cheapest(rel);
}

/* quick-and-dirty test to see if any joining is needed */
static bool
has_multiple_baserels(PlannerInfo *root)
{
    int         num_base_rels = 0;
    Index       rti;

    for (rti = 1; rti < root->simple_rel_array_size; rti++)
    {
        RelOptInfo *brel = root->simple_rel_array[rti];

        if (brel == NULL)
            continue;

        /* ignore RTEs that are "other rels" */
        if (brel->reloptkind == RELOPT_BASEREL)
            if (++num_base_rels > 1)
                return true;
    }
    return false;
}

/*
 * set_subquery_pathlist
 *      Generate SubqueryScan access paths for a subquery RTE
 *
 * We don't currently support generating parameterized paths for subqueries
 * by pushing join clauses down into them; it seems too expensive to re-plan
 * the subquery multiple times to consider different alternatives.
 * (XXX that could stand to be reconsidered, now that we use Paths.)
 * So the paths made here will be parameterized if the subquery contains
 * LATERAL references, otherwise not.  As long as that's true, there's no need
 * for a separate set_subquery_size phase: just make the paths right away.
 */
static void
set_subquery_pathlist(PlannerInfo *root, RelOptInfo *rel,
                      Index rti, RangeTblEntry *rte)
{
    Query      *parse = root->parse;
    Query      *subquery = rte->subquery;
    Relids      required_outer;
    pushdown_safety_info safetyInfo;
    double      tuple_fraction;
    RelOptInfo *sub_final_rel;
    ListCell   *lc;

    /*
     * Must copy the Query so that planning doesn't mess up the RTE contents
     * (really really need to fix the planner to not scribble on its input,
     * someday ... but see remove_unused_subquery_outputs to start with).
     */
    subquery = copyObject(subquery);

    /*
     * If it's a LATERAL subquery, it might contain some Vars of the current
     * query level, requiring it to be treated as parameterized, even though
     * we don't support pushing down join quals into subqueries.
     */
    required_outer = rel->lateral_relids;

    /*
     * Zero out result area for subquery_is_pushdown_safe, so that it can set
     * flags as needed while recursing.  In particular, we need a workspace
     * for keeping track of unsafe-to-reference columns.  unsafeColumns[i]
     * will be set true if we find that output column i of the subquery is
     * unsafe to use in a pushed-down qual.
     */
    memset(&safetyInfo, 0, sizeof(safetyInfo));
    safetyInfo.unsafeColumns = (bool *)
        palloc0((list_length(subquery->targetList) + 1) * sizeof(bool));

    /*
     * If the subquery has the "security_barrier" flag, it means the subquery
     * originated from a view that must enforce row level security.  Then we
     * must not push down quals that contain leaky functions.  (Ideally this
     * would be checked inside subquery_is_pushdown_safe, but since we don't
     * currently pass the RTE to that function, we must do it here.)
     */
    safetyInfo.unsafeLeaky = rte->security_barrier;

    /*
     * If there are any restriction clauses that have been attached to the
     * subquery relation, consider pushing them down to become WHERE or HAVING
     * quals of the subquery itself.  This transformation is useful because it
     * may allow us to generate a better plan for the subquery than evaluating
     * all the subquery output rows and then filtering them.
     *
     * There are several cases where we cannot push down clauses. Restrictions
     * involving the subquery are checked by subquery_is_pushdown_safe().
     * Restrictions on individual clauses are checked by
     * qual_is_pushdown_safe().  Also, we don't want to push down
     * pseudoconstant clauses; better to have the gating node above the
     * subquery.
     *
     * Non-pushed-down clauses will get evaluated as qpquals of the
     * SubqueryScan node.
     *
     * XXX Are there any cases where we want to make a policy decision not to
     * push down a pushable qual, because it'd result in a worse plan?
     */
    if (rel->baserestrictinfo != NIL &&
        subquery_is_pushdown_safe(subquery, subquery, &safetyInfo))
    {
        /* OK to consider pushing down individual quals */
        List       *upperrestrictlist = NIL;
        ListCell   *l;

        foreach(l, rel->baserestrictinfo)
        {
            RestrictInfo *rinfo = (RestrictInfo *) lfirst(l);
            Node       *clause = (Node *) rinfo->clause;

            if (!rinfo->pseudoconstant &&
                qual_is_pushdown_safe(subquery, rti, clause, &safetyInfo))
            {
                /* Push it down */
                subquery_push_qual(subquery, rte, rti, clause);
            }
            else
            {
                /* Keep it in the upper query */
                upperrestrictlist = lappend(upperrestrictlist, rinfo);
            }
        }
        rel->baserestrictinfo = upperrestrictlist;
        /* We don't bother recomputing baserestrict_min_security */
    }

    pfree(safetyInfo.unsafeColumns);

    /*
     * The upper query might not use all the subquery's output columns; if
     * not, we can simplify.
     */
    remove_unused_subquery_outputs(subquery, rel);

    /*
     * We can safely pass the outer tuple_fraction down to the subquery if the
     * outer level has no joining, aggregation, or sorting to do. Otherwise
     * we'd better tell the subquery to plan for full retrieval. (XXX This
     * could probably be made more intelligent ...)
     */
    if (parse->hasAggs ||
        parse->groupClause ||
        parse->groupingSets ||
        parse->havingQual ||
        parse->distinctClause ||
        parse->sortClause ||
        has_multiple_baserels(root))
        tuple_fraction = 0.0;   /* default case */
    else
        tuple_fraction = root->tuple_fraction;

    /* plan_params should not be in use in current query level */
    Assert(root->plan_params == NIL);

    /* Generate a subroot and Paths for the subquery */
    rel->subroot = subquery_planner(root->glob, subquery,
                                    root,
                                    false, tuple_fraction);

    /* Isolate the params needed by this specific subplan */
    rel->subplan_params = root->plan_params;
    root->plan_params = NIL;

    /*
     * It's possible that constraint exclusion proved the subquery empty. If
     * so, it's desirable to produce an unadorned dummy path so that we will
     * recognize appropriate optimizations at this query level.
     */
    sub_final_rel = fetch_upper_rel(rel->subroot, UPPERREL_FINAL, NULL);

    if (IS_DUMMY_REL(sub_final_rel))
    {
        set_dummy_rel_pathlist(rel);
        return;
    }

    /*
     * Mark rel with estimated output rows, width, etc.  Note that we have to
     * do this before generating outer-query paths, else cost_subqueryscan is
     * not happy.
     */
    set_subquery_size_estimates(root, rel);

    /*
     * For each Path that subquery_planner produced, make a SubqueryScanPath
     * in the outer query.
     */
    foreach(lc, sub_final_rel->pathlist)
    {
        Path       *subpath = (Path *) lfirst(lc);
        List       *pathkeys;

        /* Convert subpath's pathkeys to outer representation */
        pathkeys = convert_subquery_pathkeys(root,
                                             rel,
                                             subpath->pathkeys,
                                             make_tlist_from_pathtarget(subpath->pathtarget));

        /* Generate outer path using this subpath */
        add_path(rel, (Path *)
                 create_subqueryscan_path(root, rel, subpath,
                                          pathkeys, required_outer));
    }

    /* If outer rel allows parallelism, do same for partial paths. */
    if (rel->consider_parallel && bms_is_empty(required_outer))
    {
        /* If consider_parallel is false, there should be no partial paths. */
        Assert(sub_final_rel->consider_parallel ||
               sub_final_rel->partial_pathlist == NIL);

        /* Same for partial paths. */
        foreach(lc, sub_final_rel->partial_pathlist)
        {
            Path       *subpath = (Path *) lfirst(lc);
            List       *pathkeys;

            /* Convert subpath's pathkeys to outer representation */
            pathkeys = convert_subquery_pathkeys(root,
                                                 rel,
                                                 subpath->pathkeys,
                                                 make_tlist_from_pathtarget(subpath->pathtarget));

            /* Generate outer path using this subpath */
            add_partial_path(rel, (Path *)
                             create_subqueryscan_path(root, rel, subpath,
                                                      pathkeys,
                                                      required_outer));
        }
    }
}

/*
 * set_function_pathlist
 *      Build the (single) access path for a function RTE
 */
static void
set_function_pathlist(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte)
{
    Relids      required_outer;
    List       *pathkeys = NIL;

    /*
     * We don't support pushing join clauses into the quals of a function
     * scan, but it could still have required parameterization due to LATERAL
     * refs in the function expression.
     */
    required_outer = rel->lateral_relids;

    /*
     * The result is considered unordered unless ORDINALITY was used, in which
     * case it is ordered by the ordinal column (the last one).  See if we
     * care, by checking for uses of that Var in equivalence classes.
     */
    if (rte->funcordinality)
    {
        AttrNumber  ordattno = rel->max_attr;
        Var        *var = NULL;
        ListCell   *lc;

        /*
         * Is there a Var for it in rel's targetlist?  If not, the query did
         * not reference the ordinality column, or at least not in any way
         * that would be interesting for sorting.
         */
        foreach(lc, rel->reltarget->exprs)
        {
            Var        *node = (Var *) lfirst(lc);

            /* checking varno/varlevelsup is just paranoia */
            if (IsA(node, Var) &&
                node->varattno == ordattno &&
                node->varno == rel->relid &&
                node->varlevelsup == 0)
            {
                var = node;
                break;
            }
        }

        /*
         * Try to build pathkeys for this Var with int8 sorting.  We tell
         * build_expression_pathkey not to build any new equivalence class; if
         * the Var isn't already mentioned in some EC, it means that nothing
         * cares about the ordering.
         */
        if (var)
            pathkeys = build_expression_pathkey(root,
                                                (Expr *) var,
                                                NULL,   /* below outer joins */
                                                Int8LessOperator,
                                                rel->relids,
                                                false);
    }

    /* Generate appropriate path */
    add_path(rel, create_functionscan_path(root, rel,
                                           pathkeys, required_outer));
}

/*
 * set_values_pathlist
 *      Build the (single) access path for a VALUES RTE
 */
static void
set_values_pathlist(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte)
{
    Relids      required_outer;

    /*
     * We don't support pushing join clauses into the quals of a values scan,
     * but it could still have required parameterization due to LATERAL refs
     * in the values expressions.
     */
    required_outer = rel->lateral_relids;

    /* Generate appropriate path */
    add_path(rel, create_valuesscan_path(root, rel, required_outer));
}

/*
 * set_tablefunc_pathlist
 *      Build the (single) access path for a table func RTE
 */
static void
set_tablefunc_pathlist(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte)
{
    Relids      required_outer;

    /*
     * We don't support pushing join clauses into the quals of a tablefunc
     * scan, but it could still have required parameterization due to LATERAL
     * refs in the function expression.
     */
    required_outer = rel->lateral_relids;

    /* Generate appropriate path */
    add_path(rel, create_tablefuncscan_path(root, rel,
                                            required_outer));
}

/*
 * set_cte_pathlist
 *      Build the (single) access path for a non-self-reference CTE RTE
 *
 * There's no need for a separate set_cte_size phase, since we don't
 * support join-qual-parameterized paths for CTEs.
 */
static void
set_cte_pathlist(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte)
{
    Plan       *cteplan;
    PlannerInfo *cteroot;
    Index       levelsup;
    int         ndx;
    ListCell   *lc;
    int         plan_id;
    Relids      required_outer;

    /*
     * Find the referenced CTE, and locate the plan previously made for it.
     */
    levelsup = rte->ctelevelsup;
    cteroot = root;
    while (levelsup-- > 0)
    {
        cteroot = cteroot->parent_root;
        if (!cteroot)           /* shouldn't happen */
            elog(ERROR, "bad levelsup for CTE \"%s\"", rte->ctename);
    }

    /*
     * Note: cte_plan_ids can be shorter than cteList, if we are still working
     * on planning the CTEs (ie, this is a side-reference from another CTE).
     * So we mustn't use forboth here.
     */
    ndx = 0;
    foreach(lc, cteroot->parse->cteList)
    {
        CommonTableExpr *cte = (CommonTableExpr *) lfirst(lc);

        if (strcmp(cte->ctename, rte->ctename) == 0)
            break;
        ndx++;
    }
    if (lc == NULL)             /* shouldn't happen */
        elog(ERROR, "could not find CTE \"%s\"", rte->ctename);
    if (ndx >= list_length(cteroot->cte_plan_ids))
        elog(ERROR, "could not find plan for CTE \"%s\"", rte->ctename);
    plan_id = list_nth_int(cteroot->cte_plan_ids, ndx);
    Assert(plan_id > 0);
    cteplan = (Plan *) list_nth(root->glob->subplans, plan_id - 1);

    /* Mark rel with estimated output rows, width, etc */
    set_cte_size_estimates(root, rel, cteplan->plan_rows);

    /*
     * We don't support pushing join clauses into the quals of a CTE scan, but
     * it could still have required parameterization due to LATERAL refs in
     * its tlist.
     */
    required_outer = rel->lateral_relids;

    /* Generate appropriate path */
    add_path(rel, create_ctescan_path(root, rel, required_outer));
}

/*
 * set_namedtuplestore_pathlist
 *      Build the (single) access path for a named tuplestore RTE
 *
 * There's no need for a separate set_namedtuplestore_size phase, since we
 * don't support join-qual-parameterized paths for tuplestores.
 */
static void
set_namedtuplestore_pathlist(PlannerInfo *root, RelOptInfo *rel,
                             RangeTblEntry *rte)
{
    Relids      required_outer;

    /* Mark rel with estimated output rows, width, etc */
    set_namedtuplestore_size_estimates(root, rel);

    /*
     * We don't support pushing join clauses into the quals of a tuplestore
     * scan, but it could still have required parameterization due to LATERAL
     * refs in its tlist.
     */
    required_outer = rel->lateral_relids;

    /* Generate appropriate path */
    add_path(rel, create_namedtuplestorescan_path(root, rel, required_outer));

    /* Select cheapest path (pretty easy in this case...) */
    set_cheapest(rel);
}

/*
 * set_result_pathlist
 *      Build the (single) access path for an RTE_RESULT RTE
 *
 * There's no need for a separate set_result_size phase, since we
 * don't support join-qual-parameterized paths for these RTEs.
 */
static void
set_result_pathlist(PlannerInfo *root, RelOptInfo *rel,
                    RangeTblEntry *rte)
{
    Relids      required_outer;

    /* Mark rel with estimated output rows, width, etc */
    set_result_size_estimates(root, rel);

    /*
     * We don't support pushing join clauses into the quals of a Result scan,
     * but it could still have required parameterization due to LATERAL refs
     * in its tlist.
     */
    required_outer = rel->lateral_relids;

    /* Generate appropriate path */
    add_path(rel, create_resultscan_path(root, rel, required_outer));

    /* Select cheapest path (pretty easy in this case...) */
    set_cheapest(rel);
}

/*
 * set_worktable_pathlist
 *      Build the (single) access path for a self-reference CTE RTE
 *
 * There's no need for a separate set_worktable_size phase, since we don't
 * support join-qual-parameterized paths for CTEs.
 */
static void
set_worktable_pathlist(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte)
{
    Path       *ctepath;
    PlannerInfo *cteroot;
    Index       levelsup;
    Relids      required_outer;

    /*
     * We need to find the non-recursive term's path, which is in the plan
     * level that's processing the recursive UNION, which is one level *below*
     * where the CTE comes from.
     */
    levelsup = rte->ctelevelsup;
    if (levelsup == 0)          /* shouldn't happen */
        elog(ERROR, "bad levelsup for CTE \"%s\"", rte->ctename);
    levelsup--;
    cteroot = root;
    while (levelsup-- > 0)
    {
        cteroot = cteroot->parent_root;
        if (!cteroot)           /* shouldn't happen */
            elog(ERROR, "bad levelsup for CTE \"%s\"", rte->ctename);
    }
    ctepath = cteroot->non_recursive_path;
    if (!ctepath)               /* shouldn't happen */
        elog(ERROR, "could not find path for CTE \"%s\"", rte->ctename);

    /* Mark rel with estimated output rows, width, etc */
    set_cte_size_estimates(root, rel, ctepath->rows);

    /*
     * We don't support pushing join clauses into the quals of a worktable
     * scan, but it could still have required parameterization due to LATERAL
     * refs in its tlist.  (I'm not sure this is actually possible given the
     * restrictions on recursive references, but it's easy enough to support.)
     */
    required_outer = rel->lateral_relids;

    /* Generate appropriate path */
    add_path(rel, create_worktablescan_path(root, rel, required_outer));
}

/*
 * generate_gather_paths
 *      Generate parallel access paths for a relation by pushing a Gather or
 *      Gather Merge on top of a partial path.
 *
 * This must not be called until after we're done creating all partial paths
 * for the specified relation.  (Otherwise, add_partial_path might delete a
 * path that some GatherPath or GatherMergePath has a reference to.)
 *
 * If we're generating paths for a scan or join relation, override_rows will
 * be false, and we'll just use the relation's size estimate.  When we're
 * being called for a partially-grouped path, though, we need to override
 * the rowcount estimate.  (It's not clear that the particular value we're
 * using here is actually best, but the underlying rel has no estimate so
 * we must do something.)
 */
void
generate_gather_paths(PlannerInfo *root, RelOptInfo *rel, bool override_rows)
{
    Path       *cheapest_partial_path;
    Path       *simple_gather_path;
    ListCell   *lc;
    double      rows;
    double     *rowsp = NULL;

    /* If there are no partial paths, there's nothing to do here. */
    if (rel->partial_pathlist == NIL)
        return;

    /* Should we override the rel's rowcount estimate? */
    if (override_rows)
        rowsp = &rows;

    /*
     * The output of Gather is always unsorted, so there's only one partial
     * path of interest: the cheapest one.  That will be the one at the front
     * of partial_pathlist because of the way add_partial_path works.
     */
    cheapest_partial_path = linitial(rel->partial_pathlist);
    rows =
        cheapest_partial_path->rows * cheapest_partial_path->parallel_workers;
    simple_gather_path = (Path *)
        create_gather_path(root, rel, cheapest_partial_path, rel->reltarget,
                           NULL, rowsp);
    add_path(rel, simple_gather_path);

    /*
     * For each useful ordering, we can consider an order-preserving Gather
     * Merge.
     */
    foreach(lc, rel->partial_pathlist)
    {
        Path       *subpath = (Path *) lfirst(lc);
        GatherMergePath *path;

        if (subpath->pathkeys == NIL)
            continue;

        rows = subpath->rows * subpath->parallel_workers;
        path = create_gather_merge_path(root, rel, subpath, rel->reltarget,
                                        subpath->pathkeys, NULL, rowsp);
        add_path(rel, &path->path);
    }
}

/*
 * get_useful_pathkeys_for_relation
 *      Determine which orderings of a relation might be useful.
 *
 * Getting data in sorted order can be useful either because the requested
 * order matches the final output ordering for the overall query we're
 * planning, or because it enables an efficient merge join.  Here, we try
 * to figure out which pathkeys to consider.
 *
 * This allows us to do incremental sort on top of an index scan under a gather
 * merge node, i.e. parallelized.
 *
 * If the require_parallel_safe is true, we also require the expressions to
 * be parallel safe (which allows pushing the sort below Gather Merge).
 *
 * XXX At the moment this can only ever return a list with a single element,
 * because it looks at query_pathkeys only. So we might return the pathkeys
 * directly, but it seems plausible we'll want to consider other orderings
 * in the future. For example, we might want to consider pathkeys useful for
 * merge joins.
 */
static List *
get_useful_pathkeys_for_relation(PlannerInfo *root, RelOptInfo *rel,
                                 bool require_parallel_safe)
{
    List       *useful_pathkeys_list = NIL;

    /*
     * Considering query_pathkeys is always worth it, because it might allow
     * us to avoid a total sort when we have a partially presorted path
     * available or to push the total sort into the parallel portion of the
     * query.
     */
    if (root->query_pathkeys)
    {
        ListCell   *lc;
        int         npathkeys = 0;  /* useful pathkeys */

        foreach(lc, root->query_pathkeys)
        {
            PathKey    *pathkey = (PathKey *) lfirst(lc);
            EquivalenceClass *pathkey_ec = pathkey->pk_eclass;

            /*
             * We can only build a sort for pathkeys which contain an EC
             * member in the current relation's target, so ignore any suffix
             * of the list as soon as we find a pathkey without an EC member
             * in the relation.
             *
             * By still returning the prefix of the pathkeys list that does
             * meet criteria of EC membership in the current relation, we
             * enable not just an incremental sort on the entirety of
             * query_pathkeys but also incremental sort below a JOIN.
             *
             * If requested, ensure the expression is parallel safe too.
             */
            if (!find_em_expr_usable_for_sorting_rel(root, pathkey_ec, rel,
                                                     require_parallel_safe))
                break;

            npathkeys++;
        }

        /*
         * The whole query_pathkeys list matches, so append it directly, to
         * allow comparing pathkeys easily by comparing list pointer. If we
         * have to truncate the pathkeys, we gotta do a copy though.
         */
        if (npathkeys == list_length(root->query_pathkeys))
            useful_pathkeys_list = lappend(useful_pathkeys_list,
                                           root->query_pathkeys);
        else if (npathkeys > 0)
            useful_pathkeys_list = lappend(useful_pathkeys_list,
                                           list_truncate(list_copy(root->query_pathkeys),
                                                         npathkeys));
    }

    return useful_pathkeys_list;
}

/*
 * generate_useful_gather_paths
 *      Generate parallel access paths for a relation by pushing a Gather or
 *      Gather Merge on top of a partial path.
 *
 * Unlike plain generate_gather_paths, this looks both at pathkeys of input
 * paths (aiming to preserve the ordering), but also considers ordering that
 * might be useful for nodes above the gather merge node, and tries to add
 * a sort (regular or incremental) to provide that.
 */
void
generate_useful_gather_paths(PlannerInfo *root, RelOptInfo *rel, bool override_rows)
{
    ListCell   *lc;
    double      rows;
    double     *rowsp = NULL;
    List       *useful_pathkeys_list = NIL;
    Path       *cheapest_partial_path = NULL;

    /* If there are no partial paths, there's nothing to do here. */
    if (rel->partial_pathlist == NIL)
        return;

    /* Should we override the rel's rowcount estimate? */
    if (override_rows)
        rowsp = &rows;

    /* generate the regular gather (merge) paths */
    generate_gather_paths(root, rel, override_rows);

    /* consider incremental sort for interesting orderings */
    useful_pathkeys_list = get_useful_pathkeys_for_relation(root, rel, true);

    /* used for explicit (full) sort paths */
    cheapest_partial_path = linitial(rel->partial_pathlist);

    /*
     * Consider sorted paths for each interesting ordering. We generate both
     * incremental and full sort.
     */
    foreach(lc, useful_pathkeys_list)
    {
        List       *useful_pathkeys = lfirst(lc);
        ListCell   *lc2;
        bool        is_sorted;
        int         presorted_keys;

        foreach(lc2, rel->partial_pathlist)
        {
            Path       *subpath = (Path *) lfirst(lc2);
            GatherMergePath *path;

            is_sorted = pathkeys_count_contained_in(useful_pathkeys,
                                                    subpath->pathkeys,
                                                    &presorted_keys);

            /*
             * We don't need to consider the case where a subpath is already
             * fully sorted because generate_gather_paths already creates a
             * gather merge path for every subpath that has pathkeys present.
             *
             * But since the subpath is already sorted, we know we don't need
             * to consider adding a sort (other either kind) on top of it, so
             * we can continue here.
             */
            if (is_sorted)
                continue;

            /*
             * Consider regular sort for the cheapest partial path (for each
             * useful pathkeys). We know the path is not sorted, because we'd
             * not get here otherwise.
             *
             * This is not redundant with the gather paths created in
             * generate_gather_paths, because that doesn't generate ordered
             * output. Here we add an explicit sort to match the useful
             * ordering.
             */
            if (cheapest_partial_path == subpath)
            {
                Path       *tmp;

                tmp = (Path *) create_sort_path(root,
                                                rel,
                                                subpath,
                                                useful_pathkeys,
                                                -1.0);

                rows = tmp->rows * tmp->parallel_workers;

                path = create_gather_merge_path(root, rel,
                                                tmp,
                                                rel->reltarget,
                                                tmp->pathkeys,
                                                NULL,
                                                rowsp);

                add_path(rel, &path->path);

                /* Fall through */
            }

            /*
             * Consider incremental sort, but only when the subpath is already
             * partially sorted on a pathkey prefix.
             */
            if (enable_incremental_sort && presorted_keys > 0)
            {
                Path       *tmp;

                /*
                 * We should have already excluded pathkeys of length 1
                 * because then presorted_keys > 0 would imply is_sorted was
                 * true.
                 */
                Assert(list_length(useful_pathkeys) != 1);

                tmp = (Path *) create_incremental_sort_path(root,
                                                            rel,
                                                            subpath,
                                                            useful_pathkeys,
                                                            presorted_keys,
                                                            -1);

                path = create_gather_merge_path(root, rel,
                                                tmp,
                                                rel->reltarget,
                                                tmp->pathkeys,
                                                NULL,
                                                rowsp);

                add_path(rel, &path->path);
            }
        }
    }
}

/*
 * make_rel_from_joinlist
 *    Build access paths using a "joinlist" to guide the join path search.
 *
 * See comments for deconstruct_jointree() for definition of the joinlist
 * data structure.
 */
static RelOptInfo *
make_rel_from_joinlist(PlannerInfo *root, List *joinlist)
{
    int         levels_needed;
    List       *initial_rels;
    ListCell   *jl;

    /*
     * Count the number of child joinlist nodes.  This is the depth of the
     * dynamic-programming algorithm we must employ to consider all ways of
     * joining the child nodes.
     */
    levels_needed = list_length(joinlist);

    if (levels_needed <= 0)
        return NULL;            /* nothing to do? */

    /*
     * Construct a list of rels corresponding to the child joinlist nodes.
     * This may contain both base rels and rels constructed according to
     * sub-joinlists.
     */
    initial_rels = NIL;
    foreach(jl, joinlist)
    {
        Node       *jlnode = (Node *) lfirst(jl);
        RelOptInfo *thisrel;

        if (IsA(jlnode, RangeTblRef))
        {
            int         varno = ((RangeTblRef *) jlnode)->rtindex;

            thisrel = find_base_rel(root, varno);
        }
        else if (IsA(jlnode, List))
        {
            /* Recurse to handle subproblem */
            thisrel = make_rel_from_joinlist(root, (List *) jlnode);
        }
        else
        {
            elog(ERROR, "unrecognized joinlist node type: %d",
                 (int) nodeTag(jlnode));
            thisrel = NULL;     /* keep compiler quiet */
        }

        initial_rels = lappend(initial_rels, thisrel);
    }

    if (levels_needed == 1)
    {
        /*
         * Single joinlist node, so we're done.
         */
        return (RelOptInfo *) linitial(initial_rels);
    }
    else
    {
        /*
         * Consider the different orders in which we could join the rels,
         * using a plugin, GEQO, or the regular join search code.
         *
         * We put the initial_rels list into a PlannerInfo field because
         * has_legal_joinclause() needs to look at it (ugly :-().
         */
        root->initial_rels = initial_rels;

        if (join_search_hook)
            return (*join_search_hook) (root, levels_needed, initial_rels);
        else if (enable_geqo && levels_needed >= geqo_threshold)
            return geqo(root, levels_needed, initial_rels);
        else
            return standard_join_search(root, levels_needed, initial_rels);
    }
}

/*
 * standard_join_search
 *    Find possible joinpaths for a query by successively finding ways
 *    to join component relations into join relations.
 *
 * 'levels_needed' is the number of iterations needed, ie, the number of
 *      independent jointree items in the query.  This is > 1.
 *
 * 'initial_rels' is a list of RelOptInfo nodes for each independent
 *      jointree item.  These are the components to be joined together.
 *      Note that levels_needed == list_length(initial_rels).
 *
 * Returns the final level of join relations, i.e., the relation that is
 * the result of joining all the original relations together.
 * At least one implementation path must be provided for this relation and
 * all required sub-relations.
 *
 * To support loadable plugins that modify planner behavior by changing the
 * join searching algorithm, we provide a hook variable that lets a plugin
 * replace or supplement this function.  Any such hook must return the same
 * final join relation as the standard code would, but it might have a
 * different set of implementation paths attached, and only the sub-joinrels
 * needed for these paths need have been instantiated.
 *
 * Note to plugin authors: the functions invoked during standard_join_search()
 * modify root->join_rel_list and root->join_rel_hash.  If you want to do more
 * than one join-order search, you'll probably need to save and restore the
 * original states of those data structures.  See geqo_eval() for an example.
 */
RelOptInfo *
standard_join_search(PlannerInfo *root, int levels_needed, List *initial_rels)
{
    int         lev;
    RelOptInfo *rel;

    /*
     * This function cannot be invoked recursively within any one planning
     * problem, so join_rel_level[] can't be in use already.
     */
    Assert(root->join_rel_level == NULL);

    /*
     * We employ a simple "dynamic programming" algorithm: we first find all
     * ways to build joins of two jointree items, then all ways to build joins
     * of three items (from two-item joins and single items), then four-item
     * joins, and so on until we have considered all ways to join all the
     * items into one rel.
     *
     * root->join_rel_level[j] is a list of all the j-item rels.  Initially we
     * set root->join_rel_level[1] to represent all the single-jointree-item
     * relations.
     */
    root->join_rel_level = (List **) palloc0((levels_needed + 1) * sizeof(List *));

    root->join_rel_level[1] = initial_rels;

    for (lev = 2; lev <= levels_needed; lev++)
    {
        ListCell   *lc;

        /*
         * Determine all possible pairs of relations to be joined at this
         * level, and build paths for making each one from every available
         * pair of lower-level relations.
         */
        join_search_one_level(root, lev);

        /*
         * Run generate_partitionwise_join_paths() and
         * generate_useful_gather_paths() for each just-processed joinrel.  We
         * could not do this earlier because both regular and partial paths
         * can get added to a particular joinrel at multiple times within
         * join_search_one_level.
         *
         * After that, we're done creating paths for the joinrel, so run
         * set_cheapest().
         */
        foreach(lc, root->join_rel_level[lev])
        {
            rel = (RelOptInfo *) lfirst(lc);

            /* Create paths for partitionwise joins. */
            generate_partitionwise_join_paths(root, rel);

            /*
             * Except for the topmost scan/join rel, consider gathering
             * partial paths.  We'll do the same for the topmost scan/join rel
             * once we know the final targetlist (see grouping_planner).
             */
            if (lev < levels_needed)
                generate_useful_gather_paths(root, rel, false);

            /* Find and save the cheapest paths for this rel */
            set_cheapest(rel);

#ifdef OPTIMIZER_DEBUG
            debug_print_rel(root, rel);
#endif
        }
    }

    /*
     * We should have a single rel at the final level.
     */
    if (root->join_rel_level[levels_needed] == NIL)
        elog(ERROR, "failed to build any %d-way joins", levels_needed);
    Assert(list_length(root->join_rel_level[levels_needed]) == 1);

    rel = (RelOptInfo *) linitial(root->join_rel_level[levels_needed]);

    root->join_rel_level = NULL;

    return rel;
}

/*****************************************************************************
 *          PUSHING QUALS DOWN INTO SUBQUERIES
 *****************************************************************************/

/*
 * subquery_is_pushdown_safe - is a subquery safe for pushing down quals?
 *
 * subquery is the particular component query being checked.  topquery
 * is the top component of a set-operations tree (the same Query if no
 * set-op is involved).
 *
 * Conditions checked here:
 *
 * 1. If the subquery has a LIMIT clause, we must not push down any quals,
 * since that could change the set of rows returned.
 *
 * 2. If the subquery contains EXCEPT or EXCEPT ALL set ops we cannot push
 * quals into it, because that could change the results.
 *
 * 3. If the subquery uses DISTINCT, we cannot push volatile quals into it.
 * This is because upper-level quals should semantically be evaluated only
 * once per distinct row, not once per original row, and if the qual is
 * volatile then extra evaluations could change the results.  (This issue
 * does not apply to other forms of aggregation such as GROUP BY, because
 * when those are present we push into HAVING not WHERE, so that the quals
 * are still applied after aggregation.)
 *
 * 4. If the subquery contains window functions, we cannot push volatile quals
 * into it.  The issue here is a bit different from DISTINCT: a volatile qual
 * might succeed for some rows of a window partition and fail for others,
 * thereby changing the partition contents and thus the window functions'
 * results for rows that remain.
 *
 * 5. If the subquery contains any set-returning functions in its targetlist,
 * we cannot push volatile quals into it.  That would push them below the SRFs
 * and thereby change the number of times they are evaluated.  Also, a
 * volatile qual could succeed for some SRF output rows and fail for others,
 * a behavior that cannot occur if it's evaluated before SRF expansion.
 *
 * 6. If the subquery has nonempty grouping sets, we cannot push down any
 * quals.  The concern here is that a qual referencing a "constant" grouping
 * column could get constant-folded, which would be improper because the value
 * is potentially nullable by grouping-set expansion.  This restriction could
 * be removed if we had a parsetree representation that shows that such
 * grouping columns are not really constant.  (There are other ideas that
 * could be used to relax this restriction, but that's the approach most
 * likely to get taken in the future.  Note that there's not much to be gained
 * so long as subquery_planner can't move HAVING clauses to WHERE within such
 * a subquery.)
 *
 * In addition, we make several checks on the subquery's output columns to see
 * if it is safe to reference them in pushed-down quals.  If output column k
 * is found to be unsafe to reference, we set safetyInfo->unsafeColumns[k]
 * to true, but we don't reject the subquery overall since column k might not
 * be referenced by some/all quals.  The unsafeColumns[] array will be
 * consulted later by qual_is_pushdown_safe().  It's better to do it this way
 * than to make the checks directly in qual_is_pushdown_safe(), because when
 * the subquery involves set operations we have to check the output
 * expressions in each arm of the set op.
 *
 * Note: pushing quals into a DISTINCT subquery is theoretically dubious:
 * we're effectively assuming that the quals cannot distinguish values that
 * the DISTINCT's equality operator sees as equal, yet there are many
 * counterexamples to that assumption.  However use of such a qual with a
 * DISTINCT subquery would be unsafe anyway, since there's no guarantee which
 * "equal" value will be chosen as the output value by the DISTINCT operation.
 * So we don't worry too much about that.  Another objection is that if the
 * qual is expensive to evaluate, running it for each original row might cost
 * more than we save by eliminating rows before the DISTINCT step.  But it
 * would be very hard to estimate that at this stage, and in practice pushdown
 * seldom seems to make things worse, so we ignore that problem too.
 *
 * Note: likewise, pushing quals into a subquery with window functions is a
 * bit dubious: the quals might remove some rows of a window partition while
 * leaving others, causing changes in the window functions' results for the
 * surviving rows.  We insist that such a qual reference only partitioning
 * columns, but again that only protects us if the qual does not distinguish
 * values that the partitioning equality operator sees as equal.  The risks
 * here are perhaps larger than for DISTINCT, since no de-duplication of rows
 * occurs and thus there is no theoretical problem with such a qual.  But
 * we'll do this anyway because the potential performance benefits are very
 * large, and we've seen no field complaints about the longstanding comparable
 * behavior with DISTINCT.
 */
static bool
subquery_is_pushdown_safe(Query *subquery, Query *topquery,
                          pushdown_safety_info *safetyInfo)
{
    SetOperationStmt *topop;

    /* Check point 1 */
    if (subquery->limitOffset != NULL || subquery->limitCount != NULL)
        return false;

    /* Check point 6 */
    if (subquery->groupClause && subquery->groupingSets)
        return false;

    /* Check points 3, 4, and 5 */
    if (subquery->distinctClause ||
        subquery->hasWindowFuncs ||
        subquery->hasTargetSRFs)
        safetyInfo->unsafeVolatile = true;

    /*
     * If we're at a leaf query, check for unsafe expressions in its target
     * list, and mark any unsafe ones in unsafeColumns[].  (Non-leaf nodes in
     * setop trees have only simple Vars in their tlists, so no need to check
     * them.)
     */
    if (subquery->setOperations == NULL)
        check_output_expressions(subquery, safetyInfo);

    /* Are we at top level, or looking at a setop component? */
    if (subquery == topquery)
    {
        /* Top level, so check any component queries */
        if (subquery->setOperations != NULL)
            if (!recurse_pushdown_safe(subquery->setOperations, topquery,
                                       safetyInfo))
                return false;
    }
    else
    {
        /* Setop component must not have more components (too weird) */
        if (subquery->setOperations != NULL)
            return false;
        /* Check whether setop component output types match top level */
        topop = castNode(SetOperationStmt, topquery->setOperations);
        Assert(topop);
        compare_tlist_datatypes(subquery->targetList,
                                topop->colTypes,
                                safetyInfo);
    }
    return true;
}

/*
 * Helper routine to recurse through setOperations tree
 */
static bool
recurse_pushdown_safe(Node *setOp, Query *topquery,
                      pushdown_safety_info *safetyInfo)
{
    if (IsA(setOp, RangeTblRef))
    {
        RangeTblRef *rtr = (RangeTblRef *) setOp;
        RangeTblEntry *rte = rt_fetch(rtr->rtindex, topquery->rtable);
        Query      *subquery = rte->subquery;

        Assert(subquery != NULL);
        return subquery_is_pushdown_safe(subquery, topquery, safetyInfo);
    }
    else if (IsA(setOp, SetOperationStmt))
    {
        SetOperationStmt *op = (SetOperationStmt *) setOp;

        /* EXCEPT is no good (point 2 for subquery_is_pushdown_safe) */
        if (op->op == SETOP_EXCEPT)
            return false;
        /* Else recurse */
        if (!recurse_pushdown_safe(op->larg, topquery, safetyInfo))
            return false;
        if (!recurse_pushdown_safe(op->rarg, topquery, safetyInfo))
            return false;
    }
    else
    {
        elog(ERROR, "unrecognized node type: %d",
             (int) nodeTag(setOp));
    }
    return true;
}

/*
 * check_output_expressions - check subquery's output expressions for safety
 *
 * There are several cases in which it's unsafe to push down an upper-level
 * qual if it references a particular output column of a subquery.  We check
 * each output column of the subquery and set unsafeColumns[k] to true if
 * that column is unsafe for a pushed-down qual to reference.  The conditions
 * checked here are:
 *
 * 1. We must not push down any quals that refer to subselect outputs that
 * return sets, else we'd introduce functions-returning-sets into the
 * subquery's WHERE/HAVING quals.
 *
 * 2. We must not push down any quals that refer to subselect outputs that
 * contain volatile functions, for fear of introducing strange results due
 * to multiple evaluation of a volatile function.
 *
 * 3. If the subquery uses DISTINCT ON, we must not push down any quals that
 * refer to non-DISTINCT output columns, because that could change the set
 * of rows returned.  (This condition is vacuous for DISTINCT, because then
 * there are no non-DISTINCT output columns, so we needn't check.  Note that
 * subquery_is_pushdown_safe already reported that we can't use volatile
 * quals if there's DISTINCT or DISTINCT ON.)
 *
 * 4. If the subquery has any window functions, we must not push down quals
 * that reference any output columns that are not listed in all the subquery's
 * window PARTITION BY clauses.  We can push down quals that use only
 * partitioning columns because they should succeed or fail identically for
 * every row of any one window partition, and totally excluding some
 * partitions will not change a window function's results for remaining
 * partitions.  (Again, this also requires nonvolatile quals, but
 * subquery_is_pushdown_safe handles that.)
 */
static void
check_output_expressions(Query *subquery, pushdown_safety_info *safetyInfo)
{
    ListCell   *lc;

    foreach(lc, subquery->targetList)
    {
        TargetEntry *tle = (TargetEntry *) lfirst(lc);

        if (tle->resjunk)
            continue;           /* ignore resjunk columns */

        /* We need not check further if output col is already known unsafe */
        if (safetyInfo->unsafeColumns[tle->resno])
            continue;

        /* Functions returning sets are unsafe (point 1) */
        if (subquery->hasTargetSRFs &&
            expression_returns_set((Node *) tle->expr))
        {
            safetyInfo->unsafeColumns[tle->resno] = true;
            continue;
        }

        /* Volatile functions are unsafe (point 2) */
        if (contain_volatile_functions((Node *) tle->expr))
        {
            safetyInfo->unsafeColumns[tle->resno] = true;
            continue;
        }

        /* If subquery uses DISTINCT ON, check point 3 */
        if (subquery->hasDistinctOn &&
            !targetIsInSortList(tle, InvalidOid, subquery->distinctClause))
        {
            /* non-DISTINCT column, so mark it unsafe */
            safetyInfo->unsafeColumns[tle->resno] = true;
            continue;
        }

        /* If subquery uses window functions, check point 4 */
        if (subquery->hasWindowFuncs &&
            !targetIsInAllPartitionLists(tle, subquery))
        {
            /* not present in all PARTITION BY clauses, so mark it unsafe */
            safetyInfo->unsafeColumns[tle->resno] = true;
            continue;
        }
    }
}

/*
 * For subqueries using UNION/UNION ALL/INTERSECT/INTERSECT ALL, we can
 * push quals into each component query, but the quals can only reference
 * subquery columns that suffer no type coercions in the set operation.
 * Otherwise there are possible semantic gotchas.  So, we check the
 * component queries to see if any of them have output types different from
 * the top-level setop outputs.  unsafeColumns[k] is set true if column k
 * has different type in any component.
 *
 * We don't have to care about typmods here: the only allowed difference
 * between set-op input and output typmods is input is a specific typmod
 * and output is -1, and that does not require a coercion.
 *
 * tlist is a subquery tlist.
 * colTypes is an OID list of the top-level setop's output column types.
 * safetyInfo->unsafeColumns[] is the result array.
 */
static void
compare_tlist_datatypes(List *tlist, List *colTypes,
                        pushdown_safety_info *safetyInfo)
{
    ListCell   *l;
    ListCell   *colType = list_head(colTypes);

    foreach(l, tlist)
    {
        TargetEntry *tle = (TargetEntry *) lfirst(l);

        if (tle->resjunk)
            continue;           /* ignore resjunk columns */
        if (colType == NULL)
            elog(ERROR, "wrong number of tlist entries");
        if (exprType((Node *) tle->expr) != lfirst_oid(colType))
            safetyInfo->unsafeColumns[tle->resno] = true;
        colType = lnext(colTypes, colType);
    }
    if (colType != NULL)
        elog(ERROR, "wrong number of tlist entries");
}

/*
 * targetIsInAllPartitionLists
 *      True if the TargetEntry is listed in the PARTITION BY clause
 *      of every window defined in the query.
 *
 * It would be safe to ignore windows not actually used by any window
 * function, but it's not easy to get that info at this stage; and it's
 * unlikely to be useful to spend any extra cycles getting it, since
 * unreferenced window definitions are probably infrequent in practice.
 */
static bool
targetIsInAllPartitionLists(TargetEntry *tle, Query *query)
{
    ListCell   *lc;

    foreach(lc, query->windowClause)
    {
        WindowClause *wc = (WindowClause *) lfirst(lc);

        if (!targetIsInSortList(tle, InvalidOid, wc->partitionClause))
            return false;
    }
    return true;
}

/*
 * qual_is_pushdown_safe - is a particular qual safe to push down?
 *
 * qual is a restriction clause applying to the given subquery (whose RTE
 * has index rti in the parent query).
 *
 * Conditions checked here:
 *
 * 1. The qual must not contain any SubPlans (mainly because I'm not sure
 * it will work correctly: SubLinks will already have been transformed into
 * SubPlans in the qual, but not in the subquery).  Note that SubLinks that
 * transform to initplans are safe, and will be accepted here because what
 * we'll see in the qual is just a Param referencing the initplan output.
 *
 * 2. If unsafeVolatile is set, the qual must not contain any volatile
 * functions.
 *
 * 3. If unsafeLeaky is set, the qual must not contain any leaky functions
 * that are passed Var nodes, and therefore might reveal values from the
 * subquery as side effects.
 *
 * 4. The qual must not refer to the whole-row output of the subquery
 * (since there is no easy way to name that within the subquery itself).
 *
 * 5. The qual must not refer to any subquery output columns that were
 * found to be unsafe to reference by subquery_is_pushdown_safe().
 */
static bool
qual_is_pushdown_safe(Query *subquery, Index rti, Node *qual,
                      pushdown_safety_info *safetyInfo)
{
    bool        safe = true;
    List       *vars;
    ListCell   *vl;

    /* Refuse subselects (point 1) */
    if (contain_subplans(qual))
        return false;

    /* Refuse volatile quals if we found they'd be unsafe (point 2) */
    if (safetyInfo->unsafeVolatile &&
        contain_volatile_functions(qual))
        return false;

    /* Refuse leaky quals if told to (point 3) */
    if (safetyInfo->unsafeLeaky &&
        contain_leaked_vars(qual))
        return false;

    /*
     * It would be unsafe to push down window function calls, but at least for
     * the moment we could never see any in a qual anyhow.  (The same applies
     * to aggregates, which we check for in pull_var_clause below.)
     */
    Assert(!contain_window_function(qual));

    /*
     * Examine all Vars used in clause.  Since it's a restriction clause, all
     * such Vars must refer to subselect output columns ... unless this is
     * part of a LATERAL subquery, in which case there could be lateral
     * references.
     */
    vars = pull_var_clause(qual, PVC_INCLUDE_PLACEHOLDERS);
    foreach(vl, vars)
    {
        Var        *var = (Var *) lfirst(vl);

        /*
         * XXX Punt if we find any PlaceHolderVars in the restriction clause.
         * It's not clear whether a PHV could safely be pushed down, and even
         * less clear whether such a situation could arise in any cases of
         * practical interest anyway.  So for the moment, just refuse to push
         * down.
         */
        if (!IsA(var, Var))
        {
            safe = false;
            break;
        }

        /*
         * Punt if we find any lateral references.  It would be safe to push
         * these down, but we'd have to convert them into outer references,
         * which subquery_push_qual lacks the infrastructure to do.  The case
         * arises so seldom that it doesn't seem worth working hard on.
         */
        if (var->varno != rti)
        {
            safe = false;
            break;
        }

        /* Subqueries have no system columns */
        Assert(var->varattno >= 0);

        /* Check point 4 */
        if (var->varattno == 0)
        {
            safe = false;
            break;
        }

        /* Check point 5 */
        if (safetyInfo->unsafeColumns[var->varattno])
        {
            safe = false;
            break;
        }
    }

    list_free(vars);

    return safe;
}

/*
 * subquery_push_qual - push down a qual that we have determined is safe
 */
static void
subquery_push_qual(Query *subquery, RangeTblEntry *rte, Index rti, Node *qual)
{
    if (subquery->setOperations != NULL)
    {
        /* Recurse to push it separately to each component query */
        recurse_push_qual(subquery->setOperations, subquery,
                          rte, rti, qual);
    }
    else
    {
        /*
         * We need to replace Vars in the qual (which must refer to outputs of
         * the subquery) with copies of the subquery's targetlist expressions.
         * Note that at this point, any uplevel Vars in the qual should have
         * been replaced with Params, so they need no work.
         *
         * This step also ensures that when we are pushing into a setop tree,
         * each component query gets its own copy of the qual.
         */
        qual = ReplaceVarsFromTargetList(qual, rti, 0, rte,
                                         subquery->targetList,
                                         REPLACEVARS_REPORT_ERROR, 0,
                                         &subquery->hasSubLinks);

        /*
         * Now attach the qual to the proper place: normally WHERE, but if the
         * subquery uses grouping or aggregation, put it in HAVING (since the
         * qual really refers to the group-result rows).
         */
        if (subquery->hasAggs || subquery->groupClause || subquery->groupingSets || subquery->havingQual)
            subquery->havingQual = make_and_qual(subquery->havingQual, qual);
        else
            subquery->jointree->quals =
                make_and_qual(subquery->jointree->quals, qual);

        /*
         * We need not change the subquery's hasAggs or hasSubLinks flags,
         * since we can't be pushing down any aggregates that weren't there
         * before, and we don't push down subselects at all.
         */
    }
}

/*
 * Helper routine to recurse through setOperations tree
 */
static void
recurse_push_qual(Node *setOp, Query *topquery,
                  RangeTblEntry *rte, Index rti, Node *qual)
{
    if (IsA(setOp, RangeTblRef))
    {
        RangeTblRef *rtr = (RangeTblRef *) setOp;
        RangeTblEntry *subrte = rt_fetch(rtr->rtindex, topquery->rtable);
        Query      *subquery = subrte->subquery;

        Assert(subquery != NULL);
        subquery_push_qual(subquery, rte, rti, qual);
    }
    else if (IsA(setOp, SetOperationStmt))
    {
        SetOperationStmt *op = (SetOperationStmt *) setOp;

        recurse_push_qual(op->larg, topquery, rte, rti, qual);
        recurse_push_qual(op->rarg, topquery, rte, rti, qual);
    }
    else
    {
        elog(ERROR, "unrecognized node type: %d",
             (int) nodeTag(setOp));
    }
}

/*****************************************************************************
 *          SIMPLIFYING SUBQUERY TARGETLISTS
 *****************************************************************************/

/*
 * remove_unused_subquery_outputs
 *      Remove subquery targetlist items we don't need
 *
 * It's possible, even likely, that the upper query does not read all the
 * output columns of the subquery.  We can remove any such outputs that are
 * not needed by the subquery itself (e.g., as sort/group columns) and do not
 * affect semantics otherwise (e.g., volatile functions can't be removed).
 * This is useful not only because we might be able to remove expensive-to-
 * compute expressions, but because deletion of output columns might allow
 * optimizations such as join removal to occur within the subquery.
 *
 * To avoid affecting column numbering in the targetlist, we don't physically
 * remove unused tlist entries, but rather replace their expressions with NULL
 * constants.  This is implemented by modifying subquery->targetList.
 */
static void
remove_unused_subquery_outputs(Query *subquery, RelOptInfo *rel)
{
    Bitmapset  *attrs_used = NULL;
    ListCell   *lc;

    /*
     * Do nothing if subquery has UNION/INTERSECT/EXCEPT: in principle we
     * could update all the child SELECTs' tlists, but it seems not worth the
     * trouble presently.
     */
    if (subquery->setOperations)
        return;

    /*
     * If subquery has regular DISTINCT (not DISTINCT ON), we're wasting our
     * time: all its output columns must be used in the distinctClause.
     */
    if (subquery->distinctClause && !subquery->hasDistinctOn)
        return;

    /*
     * Collect a bitmap of all the output column numbers used by the upper
     * query.
     *
     * Add all the attributes needed for joins or final output.  Note: we must
     * look at rel's targetlist, not the attr_needed data, because attr_needed
     * isn't computed for inheritance child rels, cf set_append_rel_size().
     * (XXX might be worth changing that sometime.)
     */
    pull_varattnos((Node *) rel->reltarget->exprs, rel->relid, &attrs_used);

    /* Add all the attributes used by un-pushed-down restriction clauses. */
    foreach(lc, rel->baserestrictinfo)
    {
        RestrictInfo *rinfo = (RestrictInfo *) lfirst(lc);

        pull_varattnos((Node *) rinfo->clause, rel->relid, &attrs_used);
    }

    /*
     * If there's a whole-row reference to the subquery, we can't remove
     * anything.
     */
    if (bms_is_member(0 - FirstLowInvalidHeapAttributeNumber, attrs_used))
        return;

    /*
     * Run through the tlist and zap entries we don't need.  It's okay to
     * modify the tlist items in-place because set_subquery_pathlist made a
     * copy of the subquery.
     */
    foreach(lc, subquery->targetList)
    {
        TargetEntry *tle = (TargetEntry *) lfirst(lc);
        Node       *texpr = (Node *) tle->expr;

        /*
         * If it has a sortgroupref number, it's used in some sort/group
         * clause so we'd better not remove it.  Also, don't remove any
         * resjunk columns, since their reason for being has nothing to do
         * with anybody reading the subquery's output.  (It's likely that
         * resjunk columns in a sub-SELECT would always have ressortgroupref
         * set, but even if they don't, it seems imprudent to remove them.)
         */
        if (tle->ressortgroupref || tle->resjunk)
            continue;

        /*
         * If it's used by the upper query, we can't remove it.
         */
        if (bms_is_member(tle->resno - FirstLowInvalidHeapAttributeNumber,
                          attrs_used))
            continue;

        /*
         * If it contains a set-returning function, we can't remove it since
         * that could change the number of rows returned by the subquery.
         */
        if (subquery->hasTargetSRFs &&
            expression_returns_set(texpr))
            continue;

        /*
         * If it contains volatile functions, we daren't remove it for fear
         * that the user is expecting their side-effects to happen.
         */
        if (contain_volatile_functions(texpr))
            continue;

        /*
         * OK, we don't need it.  Replace the expression with a NULL constant.
         * Preserve the exposed type of the expression, in case something
         * looks at the rowtype of the subquery's result.
         */
        tle->expr = (Expr *) makeNullConst(exprType(texpr),
                                           exprTypmod(texpr),
                                           exprCollation(texpr));
    }
}

/*
 * create_partial_bitmap_paths
 *    Build partial bitmap heap path for the relation
 */
void
create_partial_bitmap_paths(PlannerInfo *root, RelOptInfo *rel,
                            Path *bitmapqual)
{
    int         parallel_workers;
    double      pages_fetched;

    /* Compute heap pages for bitmap heap scan */
    pages_fetched = compute_bitmap_pages(root, rel, bitmapqual, 1.0,
                                         NULL, NULL);

    parallel_workers = compute_parallel_worker(rel, pages_fetched, -1,
                                               max_parallel_workers_per_gather);

    if (parallel_workers <= 0)
        return;

    add_partial_path(rel, (Path *) create_bitmap_heap_path(root, rel,
                                                           bitmapqual, rel->lateral_relids, 1.0, parallel_workers));
}

/*
 * Compute the number of parallel workers that should be used to scan a
 * relation.  We compute the parallel workers based on the size of the heap to
 * be scanned and the size of the index to be scanned, then choose a minimum
 * of those.
 *
 * "heap_pages" is the number of pages from the table that we expect to scan, or
 * -1 if we don't expect to scan any.
 *
 * "index_pages" is the number of pages from the index that we expect to scan, or
 * -1 if we don't expect to scan any.
 *
 * "max_workers" is caller's limit on the number of workers.  This typically
 * comes from a GUC.
 */
int
compute_parallel_worker(RelOptInfo *rel, double heap_pages, double index_pages,
                        int max_workers)
{
    int         parallel_workers = 0;

    /*
     * If the user has set the parallel_workers reloption, use that; otherwise
     * select a default number of workers.
     */
    if (rel->rel_parallel_workers != -1)
        parallel_workers = rel->rel_parallel_workers;
    else
    {
        /*
         * If the number of pages being scanned is insufficient to justify a
         * parallel scan, just return zero ... unless it's an inheritance
         * child. In that case, we want to generate a parallel path here
         * anyway.  It might not be worthwhile just for this relation, but
         * when combined with all of its inheritance siblings it may well pay
         * off.
         */
        if (rel->reloptkind == RELOPT_BASEREL &&
            ((heap_pages >= 0 && heap_pages < min_parallel_table_scan_size) ||
             (index_pages >= 0 && index_pages < min_parallel_index_scan_size)))
            return 0;

        if (heap_pages >= 0)
        {
            int         heap_parallel_threshold;
            int         heap_parallel_workers = 1;

            /*
             * Select the number of workers based on the log of the size of
             * the relation.  This probably needs to be a good deal more
             * sophisticated, but we need something here for now.  Note that
             * the upper limit of the min_parallel_table_scan_size GUC is
             * chosen to prevent overflow here.
             */
            heap_parallel_threshold = Max(min_parallel_table_scan_size, 1);
            while (heap_pages >= (BlockNumber) (heap_parallel_threshold * 3))
            {
                heap_parallel_workers++;
                heap_parallel_threshold *= 3;
                if (heap_parallel_threshold > INT_MAX / 3)
                    break;      /* avoid overflow */
            }

            parallel_workers = heap_parallel_workers;
        }

        if (index_pages >= 0)
        {
            int         index_parallel_workers = 1;
            int         index_parallel_threshold;

            /* same calculation as for heap_pages above */
            index_parallel_threshold = Max(min_parallel_index_scan_size, 1);
            while (index_pages >= (BlockNumber) (index_parallel_threshold * 3))
            {
                index_parallel_workers++;
                index_parallel_threshold *= 3;
                if (index_parallel_threshold > INT_MAX / 3)
                    break;      /* avoid overflow */
            }

            if (parallel_workers > 0)
                parallel_workers = Min(parallel_workers, index_parallel_workers);
            else
                parallel_workers = index_parallel_workers;
        }
    }

    /* In no case use more than caller supplied maximum number of workers */
    parallel_workers = Min(parallel_workers, max_workers);

    return parallel_workers;
}

/*
 * generate_partitionwise_join_paths
 *      Create paths representing partitionwise join for given partitioned
 *      join relation.
 *
 * This must not be called until after we are done adding paths for all
 * child-joins. Otherwise, add_path might delete a path to which some path
 * generated here has a reference.
 */
void
generate_partitionwise_join_paths(PlannerInfo *root, RelOptInfo *rel)
{
    List       *live_children = NIL;
    int         cnt_parts;
    int         num_parts;
    RelOptInfo **part_rels;

    /* Handle only join relations here. */
    if (!IS_JOIN_REL(rel))
        return;

    /* We've nothing to do if the relation is not partitioned. */
    if (!IS_PARTITIONED_REL(rel))
        return;

    /* The relation should have consider_partitionwise_join set. */
    Assert(rel->consider_partitionwise_join);

    /* Guard against stack overflow due to overly deep partition hierarchy. */
    check_stack_depth();

    num_parts = rel->nparts;
    part_rels = rel->part_rels;

    /* Collect non-dummy child-joins. */
    for (cnt_parts = 0; cnt_parts < num_parts; cnt_parts++)
    {
        RelOptInfo *child_rel = part_rels[cnt_parts];

        /* If it's been pruned entirely, it's certainly dummy. */
        if (child_rel == NULL)
            continue;

        /* Add partitionwise join paths for partitioned child-joins. */
        generate_partitionwise_join_paths(root, child_rel);

        set_cheapest(child_rel);

        /* Dummy children will not be scanned, so ignore those. */
        if (IS_DUMMY_REL(child_rel))
            continue;

#ifdef OPTIMIZER_DEBUG
        debug_print_rel(root, child_rel);
#endif

        live_children = lappend(live_children, child_rel);
    }

    /* If all child-joins are dummy, parent join is also dummy. */
    if (!live_children)
    {
        mark_dummy_rel(rel);
        return;
    }

    /* Build additional paths for this rel from child-join paths. */
    add_paths_to_append_rel(root, rel, live_children);
    list_free(live_children);
}


/*****************************************************************************
 *          DEBUG SUPPORT
 *****************************************************************************/

#ifdef OPTIMIZER_DEBUG

static void
print_relids(PlannerInfo *root, Relids relids)
{
    int         x;
    bool        first = true;

    x = -1;
    while ((x = bms_next_member(relids, x)) >= 0)
    {
        if (!first)
            printf(" ");
        if (x < root->simple_rel_array_size &&
            root->simple_rte_array[x])
            printf("%s", root->simple_rte_array[x]->eref->aliasname);
        else
            printf("%d", x);
        first = false;
    }
}

static void
print_restrictclauses(PlannerInfo *root, List *clauses)
{
    ListCell   *l;

    foreach(l, clauses)
    {
        RestrictInfo *c = lfirst(l);

        print_expr((Node *) c->clause, root->parse->rtable);
        if (lnext(clauses, l))
            printf(", ");
    }
}

static void
print_path(PlannerInfo *root, Path *path, int indent)
{
    const char *ptype;
    bool        join = false;
    Path       *subpath = NULL;
    int         i;

    switch (nodeTag(path))
    {
        case T_Path:
            switch (path->pathtype)
            {
                case T_SeqScan:
                    ptype = "SeqScan";
                    break;
                case T_SampleScan:
                    ptype = "SampleScan";
                    break;
                case T_FunctionScan:
                    ptype = "FunctionScan";
                    break;
                case T_TableFuncScan:
                    ptype = "TableFuncScan";
                    break;
                case T_ValuesScan:
                    ptype = "ValuesScan";
                    break;
                case T_CteScan:
                    ptype = "CteScan";
                    break;
                case T_NamedTuplestoreScan:
                    ptype = "NamedTuplestoreScan";
                    break;
                case T_Result:
                    ptype = "Result";
                    break;
                case T_WorkTableScan:
                    ptype = "WorkTableScan";
                    break;
                default:
                    ptype = "???Path";
                    break;
            }
            break;
        case T_IndexPath:
            ptype = "IdxScan";
            break;
        case T_BitmapHeapPath:
            ptype = "BitmapHeapScan";
            break;
        case T_BitmapAndPath:
            ptype = "BitmapAndPath";
            break;
        case T_BitmapOrPath:
            ptype = "BitmapOrPath";
            break;
        case T_TidPath:
            ptype = "TidScan";
            break;
        case T_SubqueryScanPath:
            ptype = "SubqueryScan";
            break;
        case T_ForeignPath:
            ptype = "ForeignScan";
            break;
        case T_CustomPath:
            ptype = "CustomScan";
            break;
        case T_NestPath:
            ptype = "NestLoop";
            join = true;
            break;
        case T_MergePath:
            ptype = "MergeJoin";
            join = true;
            break;
        case T_HashPath:
            ptype = "HashJoin";
            join = true;
            break;
        case T_AppendPath:
            ptype = "Append";
            break;
        case T_MergeAppendPath:
            ptype = "MergeAppend";
            break;
        case T_GroupResultPath:
            ptype = "GroupResult";
            break;
        case T_MaterialPath:
            ptype = "Material";
            subpath = ((MaterialPath *) path)->subpath;
            break;
        case T_UniquePath:
            ptype = "Unique";
            subpath = ((UniquePath *) path)->subpath;
            break;
        case T_GatherPath:
            ptype = "Gather";
            subpath = ((GatherPath *) path)->subpath;
            break;
        case T_GatherMergePath:
            ptype = "GatherMerge";
            subpath = ((GatherMergePath *) path)->subpath;
            break;
        case T_ProjectionPath:
            ptype = "Projection";
            subpath = ((ProjectionPath *) path)->subpath;
            break;
        case T_ProjectSetPath:
            ptype = "ProjectSet";
            subpath = ((ProjectSetPath *) path)->subpath;
            break;
        case T_SortPath:
            ptype = "Sort";
            subpath = ((SortPath *) path)->subpath;
            break;
        case T_IncrementalSortPath:
            ptype = "IncrementalSort";
            subpath = ((SortPath *) path)->subpath;
            break;
        case T_GroupPath:
            ptype = "Group";
            subpath = ((GroupPath *) path)->subpath;
            break;
        case T_UpperUniquePath:
            ptype = "UpperUnique";
            subpath = ((UpperUniquePath *) path)->subpath;
            break;
        case T_AggPath:
            ptype = "Agg";
            subpath = ((AggPath *) path)->subpath;
            break;
        case T_GroupingSetsPath:
            ptype = "GroupingSets";
            subpath = ((GroupingSetsPath *) path)->subpath;
            break;
        case T_MinMaxAggPath:
            ptype = "MinMaxAgg";
            break;
        case T_WindowAggPath:
            ptype = "WindowAgg";
            subpath = ((WindowAggPath *) path)->subpath;
            break;
        case T_SetOpPath:
            ptype = "SetOp";
            subpath = ((SetOpPath *) path)->subpath;
            break;
        case T_RecursiveUnionPath:
            ptype = "RecursiveUnion";
            break;
        case T_LockRowsPath:
            ptype = "LockRows";
            subpath = ((LockRowsPath *) path)->subpath;
            break;
        case T_ModifyTablePath:
            ptype = "ModifyTable";
            break;
        case T_LimitPath:
            ptype = "Limit";
            subpath = ((LimitPath *) path)->subpath;
            break;
        default:
            ptype = "???Path";
            break;
    }

    for (i = 0; i < indent; i++)
        printf("\t");
    printf("%s", ptype);

    if (path->parent)
    {
        printf("(");
        print_relids(root, path->parent->relids);
        printf(")");
    }
    if (path->param_info)
    {
        printf(" required_outer (");
        print_relids(root, path->param_info->ppi_req_outer);
        printf(")");
    }
    printf(" rows=%.0f cost=%.2f..%.2f\n",
           path->rows, path->startup_cost, path->total_cost);

    if (path->pathkeys)
    {
        for (i = 0; i < indent; i++)
            printf("\t");
        printf("  pathkeys: ");
        print_pathkeys(path->pathkeys, root->parse->rtable);
    }

    if (join)
    {
        JoinPath   *jp = (JoinPath *) path;

        for (i = 0; i < indent; i++)
            printf("\t");
        printf("  clauses: ");
        print_restrictclauses(root, jp->joinrestrictinfo);
        printf("\n");

        if (IsA(path, MergePath))
        {
            MergePath  *mp = (MergePath *) path;

            for (i = 0; i < indent; i++)
                printf("\t");
            printf("  sortouter=%d sortinner=%d materializeinner=%d\n",
                   ((mp->outersortkeys) ? 1 : 0),
                   ((mp->innersortkeys) ? 1 : 0),
                   ((mp->materialize_inner) ? 1 : 0));
        }

        print_path(root, jp->outerjoinpath, indent + 1);
        print_path(root, jp->innerjoinpath, indent + 1);
    }

    if (subpath)
        print_path(root, subpath, indent + 1);
}

void
debug_print_rel(PlannerInfo *root, RelOptInfo *rel)
{
    ListCell   *l;

    printf("RELOPTINFO (");
    print_relids(root, rel->relids);
    printf("): rows=%.0f width=%d\n", rel->rows, rel->reltarget->width);

    if (rel->baserestrictinfo)
    {
        printf("\tbaserestrictinfo: ");
        print_restrictclauses(root, rel->baserestrictinfo);
        printf("\n");
    }

    if (rel->joininfo)
    {
        printf("\tjoininfo: ");
        print_restrictclauses(root, rel->joininfo);
        printf("\n");
    }

    printf("\tpath list:\n");
    foreach(l, rel->pathlist)
        print_path(root, lfirst(l), 1);
    if (rel->cheapest_parameterized_paths)
    {
        printf("\n\tcheapest parameterized paths:\n");
        foreach(l, rel->cheapest_parameterized_paths)
            print_path(root, lfirst(l), 1);
    }
    if (rel->cheapest_startup_path)
    {
        printf("\n\tcheapest startup path:\n");
        print_path(root, rel->cheapest_startup_path, 1);
    }
    if (rel->cheapest_total_path)
    {
        printf("\n\tcheapest total path:\n");
        print_path(root, rel->cheapest_total_path, 1);
    }
    printf("\n");
    fflush(stdout);
}

#endif                          /* OPTIMIZER_DEBUG */