pathnode.c

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/*-------------------------------------------------------------------------
 *
 * pathnode.c
 *    Routines to manipulate pathlists and create path nodes
 *
 * Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/optimizer/util/pathnode.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include <math.h>

#include "foreign/fdwapi.h"
#include "miscadmin.h"
#include "nodes/extensible.h"
#include "nodes/nodeFuncs.h"
#include "optimizer/appendinfo.h"
#include "optimizer/clauses.h"
#include "optimizer/cost.h"
#include "optimizer/optimizer.h"
#include "optimizer/pathnode.h"
#include "optimizer/paths.h"
#include "optimizer/planmain.h"
#include "optimizer/prep.h"
#include "optimizer/restrictinfo.h"
#include "optimizer/tlist.h"
#include "parser/parsetree.h"
#include "utils/lsyscache.h"
#include "utils/memutils.h"
#include "utils/selfuncs.h"

typedef enum
{
    COSTS_EQUAL,                /* path costs are fuzzily equal */
    COSTS_BETTER1,              /* first path is cheaper than second */
    COSTS_BETTER2,              /* second path is cheaper than first */
    COSTS_DIFFERENT             /* neither path dominates the other on cost */
} PathCostComparison;

/*
 * STD_FUZZ_FACTOR is the normal fuzz factor for compare_path_costs_fuzzily.
 * XXX is it worth making this user-controllable?  It provides a tradeoff
 * between planner runtime and the accuracy of path cost comparisons.
 */
#define STD_FUZZ_FACTOR 1.01

static List *translate_sub_tlist(List *tlist, int relid);
static int  append_total_cost_compare(const ListCell *a, const ListCell *b);
static int  append_startup_cost_compare(const ListCell *a, const ListCell *b);
static List *reparameterize_pathlist_by_child(PlannerInfo *root,
                                              List *pathlist,
                                              RelOptInfo *child_rel);


/*****************************************************************************
 *      MISC. PATH UTILITIES
 *****************************************************************************/

/*
 * compare_path_costs
 *    Return -1, 0, or +1 according as path1 is cheaper, the same cost,
 *    or more expensive than path2 for the specified criterion.
 */
int
compare_path_costs(Path *path1, Path *path2, CostSelector criterion)
{
    if (criterion == STARTUP_COST)
    {
        if (path1->startup_cost < path2->startup_cost)
            return -1;
        if (path1->startup_cost > path2->startup_cost)
            return +1;

        /*
         * If paths have the same startup cost (not at all unlikely), order
         * them by total cost.
         */
        if (path1->total_cost < path2->total_cost)
            return -1;
        if (path1->total_cost > path2->total_cost)
            return +1;
    }
    else
    {
        if (path1->total_cost < path2->total_cost)
            return -1;
        if (path1->total_cost > path2->total_cost)
            return +1;

        /*
         * If paths have the same total cost, order them by startup cost.
         */
        if (path1->startup_cost < path2->startup_cost)
            return -1;
        if (path1->startup_cost > path2->startup_cost)
            return +1;
    }
    return 0;
}

/*
 * compare_path_fractional_costs
 *    Return -1, 0, or +1 according as path1 is cheaper, the same cost,
 *    or more expensive than path2 for fetching the specified fraction
 *    of the total tuples.
 *
 * If fraction is <= 0 or > 1, we interpret it as 1, ie, we select the
 * path with the cheaper total_cost.
 */
int
compare_fractional_path_costs(Path *path1, Path *path2,
                              double fraction)
{
    Cost        cost1,
                cost2;

    if (fraction <= 0.0 || fraction >= 1.0)
        return compare_path_costs(path1, path2, TOTAL_COST);
    cost1 = path1->startup_cost +
        fraction * (path1->total_cost - path1->startup_cost);
    cost2 = path2->startup_cost +
        fraction * (path2->total_cost - path2->startup_cost);
    if (cost1 < cost2)
        return -1;
    if (cost1 > cost2)
        return +1;
    return 0;
}

/*
 * compare_path_costs_fuzzily
 *    Compare the costs of two paths to see if either can be said to
 *    dominate the other.
 *
 * We use fuzzy comparisons so that add_path() can avoid keeping both of
 * a pair of paths that really have insignificantly different cost.
 *
 * The fuzz_factor argument must be 1.0 plus delta, where delta is the
 * fraction of the smaller cost that is considered to be a significant
 * difference.  For example, fuzz_factor = 1.01 makes the fuzziness limit
 * be 1% of the smaller cost.
 *
 * The two paths are said to have "equal" costs if both startup and total
 * costs are fuzzily the same.  Path1 is said to be better than path2 if
 * it has fuzzily better startup cost and fuzzily no worse total cost,
 * or if it has fuzzily better total cost and fuzzily no worse startup cost.
 * Path2 is better than path1 if the reverse holds.  Finally, if one path
 * is fuzzily better than the other on startup cost and fuzzily worse on
 * total cost, we just say that their costs are "different", since neither
 * dominates the other across the whole performance spectrum.
 *
 * This function also enforces a policy rule that paths for which the relevant
 * one of parent->consider_startup and parent->consider_param_startup is false
 * cannot survive comparisons solely on the grounds of good startup cost, so
 * we never return COSTS_DIFFERENT when that is true for the total-cost loser.
 * (But if total costs are fuzzily equal, we compare startup costs anyway,
 * in hopes of eliminating one path or the other.)
 */
static PathCostComparison
compare_path_costs_fuzzily(Path *path1, Path *path2, double fuzz_factor)
{
#define CONSIDER_PATH_STARTUP_COST(p)  \
    ((p)->param_info == NULL ? (p)->parent->consider_startup : (p)->parent->consider_param_startup)

    /*
     * Check total cost first since it's more likely to be different; many
     * paths have zero startup cost.
     */
    if (path1->total_cost > path2->total_cost * fuzz_factor)
    {
        /* path1 fuzzily worse on total cost */
        if (CONSIDER_PATH_STARTUP_COST(path1) &&
            path2->startup_cost > path1->startup_cost * fuzz_factor)
        {
            /* ... but path2 fuzzily worse on startup, so DIFFERENT */
            return COSTS_DIFFERENT;
        }
        /* else path2 dominates */
        return COSTS_BETTER2;
    }
    if (path2->total_cost > path1->total_cost * fuzz_factor)
    {
        /* path2 fuzzily worse on total cost */
        if (CONSIDER_PATH_STARTUP_COST(path2) &&
            path1->startup_cost > path2->startup_cost * fuzz_factor)
        {
            /* ... but path1 fuzzily worse on startup, so DIFFERENT */
            return COSTS_DIFFERENT;
        }
        /* else path1 dominates */
        return COSTS_BETTER1;
    }
    /* fuzzily the same on total cost ... */
    if (path1->startup_cost > path2->startup_cost * fuzz_factor)
    {
        /* ... but path1 fuzzily worse on startup, so path2 wins */
        return COSTS_BETTER2;
    }
    if (path2->startup_cost > path1->startup_cost * fuzz_factor)
    {
        /* ... but path2 fuzzily worse on startup, so path1 wins */
        return COSTS_BETTER1;
    }
    /* fuzzily the same on both costs */
    return COSTS_EQUAL;

#undef CONSIDER_PATH_STARTUP_COST
}

/*
 * set_cheapest
 *    Find the minimum-cost paths from among a relation's paths,
 *    and save them in the rel's cheapest-path fields.
 *
 * cheapest_total_path is normally the cheapest-total-cost unparameterized
 * path; but if there are no unparameterized paths, we assign it to be the
 * best (cheapest least-parameterized) parameterized path.  However, only
 * unparameterized paths are considered candidates for cheapest_startup_path,
 * so that will be NULL if there are no unparameterized paths.
 *
 * The cheapest_parameterized_paths list collects all parameterized paths
 * that have survived the add_path() tournament for this relation.  (Since
 * add_path ignores pathkeys for a parameterized path, these will be paths
 * that have best cost or best row count for their parameterization.  We
 * may also have both a parallel-safe and a non-parallel-safe path in some
 * cases for the same parameterization in some cases, but this should be
 * relatively rare since, most typically, all paths for the same relation
 * will be parallel-safe or none of them will.)
 *
 * cheapest_parameterized_paths always includes the cheapest-total
 * unparameterized path, too, if there is one; the users of that list find
 * it more convenient if that's included.
 *
 * This is normally called only after we've finished constructing the path
 * list for the rel node.
 */
void
set_cheapest(RelOptInfo *parent_rel)
{
    Path       *cheapest_startup_path;
    Path       *cheapest_total_path;
    Path       *best_param_path;
    List       *parameterized_paths;
    ListCell   *p;

    Assert(IsA(parent_rel, RelOptInfo));

    if (parent_rel->pathlist == NIL)
        elog(ERROR, "could not devise a query plan for the given query");

    cheapest_startup_path = cheapest_total_path = best_param_path = NULL;
    parameterized_paths = NIL;

    foreach(p, parent_rel->pathlist)
    {
        Path       *path = (Path *) lfirst(p);
        int         cmp;

        if (path->param_info)
        {
            /* Parameterized path, so add it to parameterized_paths */
            parameterized_paths = lappend(parameterized_paths, path);

            /*
             * If we have an unparameterized cheapest-total, we no longer care
             * about finding the best parameterized path, so move on.
             */
            if (cheapest_total_path)
                continue;

            /*
             * Otherwise, track the best parameterized path, which is the one
             * with least total cost among those of the minimum
             * parameterization.
             */
            if (best_param_path == NULL)
                best_param_path = path;
            else
            {
                switch (bms_subset_compare(PATH_REQ_OUTER(path),
                                           PATH_REQ_OUTER(best_param_path)))
                {
                    case BMS_EQUAL:
                        /* keep the cheaper one */
                        if (compare_path_costs(path, best_param_path,
                                               TOTAL_COST) < 0)
                            best_param_path = path;
                        break;
                    case BMS_SUBSET1:
                        /* new path is less-parameterized */
                        best_param_path = path;
                        break;
                    case BMS_SUBSET2:
                        /* old path is less-parameterized, keep it */
                        break;
                    case BMS_DIFFERENT:

                        /*
                         * This means that neither path has the least possible
                         * parameterization for the rel.  We'll sit on the old
                         * path until something better comes along.
                         */
                        break;
                }
            }
        }
        else
        {
            /* Unparameterized path, so consider it for cheapest slots */
            if (cheapest_total_path == NULL)
            {
                cheapest_startup_path = cheapest_total_path = path;
                continue;
            }

            /*
             * If we find two paths of identical costs, try to keep the
             * better-sorted one.  The paths might have unrelated sort
             * orderings, in which case we can only guess which might be
             * better to keep, but if one is superior then we definitely
             * should keep that one.
             */
            cmp = compare_path_costs(cheapest_startup_path, path, STARTUP_COST);
            if (cmp > 0 ||
                (cmp == 0 &&
                 compare_pathkeys(cheapest_startup_path->pathkeys,
                                  path->pathkeys) == PATHKEYS_BETTER2))
                cheapest_startup_path = path;

            cmp = compare_path_costs(cheapest_total_path, path, TOTAL_COST);
            if (cmp > 0 ||
                (cmp == 0 &&
                 compare_pathkeys(cheapest_total_path->pathkeys,
                                  path->pathkeys) == PATHKEYS_BETTER2))
                cheapest_total_path = path;
        }
    }

    /* Add cheapest unparameterized path, if any, to parameterized_paths */
    if (cheapest_total_path)
        parameterized_paths = lcons(cheapest_total_path, parameterized_paths);

    /*
     * If there is no unparameterized path, use the best parameterized path as
     * cheapest_total_path (but not as cheapest_startup_path).
     */
    if (cheapest_total_path == NULL)
        cheapest_total_path = best_param_path;
    Assert(cheapest_total_path != NULL);

    parent_rel->cheapest_startup_path = cheapest_startup_path;
    parent_rel->cheapest_total_path = cheapest_total_path;
    parent_rel->cheapest_unique_path = NULL;    /* computed only if needed */
    parent_rel->cheapest_parameterized_paths = parameterized_paths;
}

/*
 * add_path
 *    Consider a potential implementation path for the specified parent rel,
 *    and add it to the rel's pathlist if it is worthy of consideration.
 *    A path is worthy if it has a better sort order (better pathkeys) or
 *    cheaper cost (on either dimension), or generates fewer rows, than any
 *    existing path that has the same or superset parameterization rels.
 *    We also consider parallel-safe paths more worthy than others.
 *
 *    We also remove from the rel's pathlist any old paths that are dominated
 *    by new_path --- that is, new_path is cheaper, at least as well ordered,
 *    generates no more rows, requires no outer rels not required by the old
 *    path, and is no less parallel-safe.
 *
 *    In most cases, a path with a superset parameterization will generate
 *    fewer rows (since it has more join clauses to apply), so that those two
 *    figures of merit move in opposite directions; this means that a path of
 *    one parameterization can seldom dominate a path of another.  But such
 *    cases do arise, so we make the full set of checks anyway.
 *
 *    There are two policy decisions embedded in this function, along with
 *    its sibling add_path_precheck.  First, we treat all parameterized paths
 *    as having NIL pathkeys, so that they cannot win comparisons on the
 *    basis of sort order.  This is to reduce the number of parameterized
 *    paths that are kept; see discussion in src/backend/optimizer/README.
 *
 *    Second, we only consider cheap startup cost to be interesting if
 *    parent_rel->consider_startup is true for an unparameterized path, or
 *    parent_rel->consider_param_startup is true for a parameterized one.
 *    Again, this allows discarding useless paths sooner.
 *
 *    The pathlist is kept sorted by total_cost, with cheaper paths
 *    at the front.  Within this routine, that's simply a speed hack:
 *    doing it that way makes it more likely that we will reject an inferior
 *    path after a few comparisons, rather than many comparisons.
 *    However, add_path_precheck relies on this ordering to exit early
 *    when possible.
 *
 *    NOTE: discarded Path objects are immediately pfree'd to reduce planner
 *    memory consumption.  We dare not try to free the substructure of a Path,
 *    since much of it may be shared with other Paths or the query tree itself;
 *    but just recycling discarded Path nodes is a very useful savings in
 *    a large join tree.  We can recycle the List nodes of pathlist, too.
 *
 *    As noted in optimizer/README, deleting a previously-accepted Path is
 *    safe because we know that Paths of this rel cannot yet be referenced
 *    from any other rel, such as a higher-level join.  However, in some cases
 *    it is possible that a Path is referenced by another Path for its own
 *    rel; we must not delete such a Path, even if it is dominated by the new
 *    Path.  Currently this occurs only for IndexPath objects, which may be
 *    referenced as children of BitmapHeapPaths as well as being paths in
 *    their own right.  Hence, we don't pfree IndexPaths when rejecting them.
 *
 * 'parent_rel' is the relation entry to which the path corresponds.
 * 'new_path' is a potential path for parent_rel.
 *
 * Returns nothing, but modifies parent_rel->pathlist.
 */
void
add_path(RelOptInfo *parent_rel, Path *new_path)
{
    bool        accept_new = true;  /* unless we find a superior old path */
    int         insert_at = 0;  /* where to insert new item */
    List       *new_path_pathkeys;
    ListCell   *p1;

    /*
     * This is a convenient place to check for query cancel --- no part of the
     * planner goes very long without calling add_path().
     */
    CHECK_FOR_INTERRUPTS();

    /* Pretend parameterized paths have no pathkeys, per comment above */
    new_path_pathkeys = new_path->param_info ? NIL : new_path->pathkeys;

    /*
     * Loop to check proposed new path against old paths.  Note it is possible
     * for more than one old path to be tossed out because new_path dominates
     * it.
     */
    foreach(p1, parent_rel->pathlist)
    {
        Path       *old_path = (Path *) lfirst(p1);
        bool        remove_old = false; /* unless new proves superior */
        PathCostComparison costcmp;
        PathKeysComparison keyscmp;
        BMS_Comparison outercmp;

        /*
         * Do a fuzzy cost comparison with standard fuzziness limit.
         */
        costcmp = compare_path_costs_fuzzily(new_path, old_path,
                                             STD_FUZZ_FACTOR);

        /*
         * If the two paths compare differently for startup and total cost,
         * then we want to keep both, and we can skip comparing pathkeys and
         * required_outer rels.  If they compare the same, proceed with the
         * other comparisons.  Row count is checked last.  (We make the tests
         * in this order because the cost comparison is most likely to turn
         * out "different", and the pathkeys comparison next most likely.  As
         * explained above, row count very seldom makes a difference, so even
         * though it's cheap to compare there's not much point in checking it
         * earlier.)
         */
        if (costcmp != COSTS_DIFFERENT)
        {
            /* Similarly check to see if either dominates on pathkeys */
            List       *old_path_pathkeys;

            old_path_pathkeys = old_path->param_info ? NIL : old_path->pathkeys;
            keyscmp = compare_pathkeys(new_path_pathkeys,
                                       old_path_pathkeys);
            if (keyscmp != PATHKEYS_DIFFERENT)
            {
                switch (costcmp)
                {
                    case COSTS_EQUAL:
                        outercmp = bms_subset_compare(PATH_REQ_OUTER(new_path),
                                                      PATH_REQ_OUTER(old_path));
                        if (keyscmp == PATHKEYS_BETTER1)
                        {
                            if ((outercmp == BMS_EQUAL ||
                                 outercmp == BMS_SUBSET1) &&
                                new_path->rows <= old_path->rows &&
                                new_path->parallel_safe >= old_path->parallel_safe)
                                remove_old = true;  /* new dominates old */
                        }
                        else if (keyscmp == PATHKEYS_BETTER2)
                        {
                            if ((outercmp == BMS_EQUAL ||
                                 outercmp == BMS_SUBSET2) &&
                                new_path->rows >= old_path->rows &&
                                new_path->parallel_safe <= old_path->parallel_safe)
                                accept_new = false; /* old dominates new */
                        }
                        else    /* keyscmp == PATHKEYS_EQUAL */
                        {
                            if (outercmp == BMS_EQUAL)
                            {
                                /*
                                 * Same pathkeys and outer rels, and fuzzily
                                 * the same cost, so keep just one; to decide
                                 * which, first check parallel-safety, then
                                 * rows, then do a fuzzy cost comparison with
                                 * very small fuzz limit.  (We used to do an
                                 * exact cost comparison, but that results in
                                 * annoying platform-specific plan variations
                                 * due to roundoff in the cost estimates.)  If
                                 * things are still tied, arbitrarily keep
                                 * only the old path.  Notice that we will
                                 * keep only the old path even if the
                                 * less-fuzzy comparison decides the startup
                                 * and total costs compare differently.
                                 */
                                if (new_path->parallel_safe >
                                    old_path->parallel_safe)
                                    remove_old = true;  /* new dominates old */
                                else if (new_path->parallel_safe <
                                         old_path->parallel_safe)
                                    accept_new = false; /* old dominates new */
                                else if (new_path->rows < old_path->rows)
                                    remove_old = true;  /* new dominates old */
                                else if (new_path->rows > old_path->rows)
                                    accept_new = false; /* old dominates new */
                                else if (compare_path_costs_fuzzily(new_path,
                                                                    old_path,
                                                                    1.0000000001) == COSTS_BETTER1)
                                    remove_old = true;  /* new dominates old */
                                else
                                    accept_new = false; /* old equals or
                                                         * dominates new */
                            }
                            else if (outercmp == BMS_SUBSET1 &&
                                     new_path->rows <= old_path->rows &&
                                     new_path->parallel_safe >= old_path->parallel_safe)
                                remove_old = true;  /* new dominates old */
                            else if (outercmp == BMS_SUBSET2 &&
                                     new_path->rows >= old_path->rows &&
                                     new_path->parallel_safe <= old_path->parallel_safe)
                                accept_new = false; /* old dominates new */
                            /* else different parameterizations, keep both */
                        }
                        break;
                    case COSTS_BETTER1:
                        if (keyscmp != PATHKEYS_BETTER2)
                        {
                            outercmp = bms_subset_compare(PATH_REQ_OUTER(new_path),
                                                          PATH_REQ_OUTER(old_path));
                            if ((outercmp == BMS_EQUAL ||
                                 outercmp == BMS_SUBSET1) &&
                                new_path->rows <= old_path->rows &&
                                new_path->parallel_safe >= old_path->parallel_safe)
                                remove_old = true;  /* new dominates old */
                        }
                        break;
                    case COSTS_BETTER2:
                        if (keyscmp != PATHKEYS_BETTER1)
                        {
                            outercmp = bms_subset_compare(PATH_REQ_OUTER(new_path),
                                                          PATH_REQ_OUTER(old_path));
                            if ((outercmp == BMS_EQUAL ||
                                 outercmp == BMS_SUBSET2) &&
                                new_path->rows >= old_path->rows &&
                                new_path->parallel_safe <= old_path->parallel_safe)
                                accept_new = false; /* old dominates new */
                        }
                        break;
                    case COSTS_DIFFERENT:

                        /*
                         * can't get here, but keep this case to keep compiler
                         * quiet
                         */
                        break;
                }
            }
        }

        /*
         * Remove current element from pathlist if dominated by new.
         */
        if (remove_old)
        {
            parent_rel->pathlist = foreach_delete_current(parent_rel->pathlist,
                                                          p1);

            /*
             * Delete the data pointed-to by the deleted cell, if possible
             */
            if (!IsA(old_path, IndexPath))
                pfree(old_path);
        }
        else
        {
            /* new belongs after this old path if it has cost >= old's */
            if (new_path->total_cost >= old_path->total_cost)
                insert_at = foreach_current_index(p1) + 1;
        }

        /*
         * If we found an old path that dominates new_path, we can quit
         * scanning the pathlist; we will not add new_path, and we assume
         * new_path cannot dominate any other elements of the pathlist.
         */
        if (!accept_new)
            break;
    }

    if (accept_new)
    {
        /* Accept the new path: insert it at proper place in pathlist */
        parent_rel->pathlist =
            list_insert_nth(parent_rel->pathlist, insert_at, new_path);
    }
    else
    {
        /* Reject and recycle the new path */
        if (!IsA(new_path, IndexPath))
            pfree(new_path);
    }
}

/*
 * add_path_precheck
 *    Check whether a proposed new path could possibly get accepted.
 *    We assume we know the path's pathkeys and parameterization accurately,
 *    and have lower bounds for its costs.
 *
 * Note that we do not know the path's rowcount, since getting an estimate for
 * that is too expensive to do before prechecking.  We assume here that paths
 * of a superset parameterization will generate fewer rows; if that holds,
 * then paths with different parameterizations cannot dominate each other
 * and so we can simply ignore existing paths of another parameterization.
 * (In the infrequent cases where that rule of thumb fails, add_path will
 * get rid of the inferior path.)
 *
 * At the time this is called, we haven't actually built a Path structure,
 * so the required information has to be passed piecemeal.
 */
bool
add_path_precheck(RelOptInfo *parent_rel,
                  Cost startup_cost, Cost total_cost,
                  List *pathkeys, Relids required_outer)
{
    List       *new_path_pathkeys;
    bool        consider_startup;
    ListCell   *p1;

    /* Pretend parameterized paths have no pathkeys, per add_path policy */
    new_path_pathkeys = required_outer ? NIL : pathkeys;

    /* Decide whether new path's startup cost is interesting */
    consider_startup = required_outer ? parent_rel->consider_param_startup : parent_rel->consider_startup;

    foreach(p1, parent_rel->pathlist)
    {
        Path       *old_path = (Path *) lfirst(p1);
        PathKeysComparison keyscmp;

        /*
         * We are looking for an old_path with the same parameterization (and
         * by assumption the same rowcount) that dominates the new path on
         * pathkeys as well as both cost metrics.  If we find one, we can
         * reject the new path.
         *
         * Cost comparisons here should match compare_path_costs_fuzzily.
         */
        if (total_cost > old_path->total_cost * STD_FUZZ_FACTOR)
        {
            /* new path can win on startup cost only if consider_startup */
            if (startup_cost > old_path->startup_cost * STD_FUZZ_FACTOR ||
                !consider_startup)
            {
                /* new path loses on cost, so check pathkeys... */
                List       *old_path_pathkeys;

                old_path_pathkeys = old_path->param_info ? NIL : old_path->pathkeys;
                keyscmp = compare_pathkeys(new_path_pathkeys,
                                           old_path_pathkeys);
                if (keyscmp == PATHKEYS_EQUAL ||
                    keyscmp == PATHKEYS_BETTER2)
                {
                    /* new path does not win on pathkeys... */
                    if (bms_equal(required_outer, PATH_REQ_OUTER(old_path)))
                    {
                        /* Found an old path that dominates the new one */
                        return false;
                    }
                }
            }
        }
        else
        {
            /*
             * Since the pathlist is sorted by total_cost, we can stop looking
             * once we reach a path with a total_cost larger than the new
             * path's.
             */
            break;
        }
    }

    return true;
}

/*
 * add_partial_path
 *    Like add_path, our goal here is to consider whether a path is worthy
 *    of being kept around, but the considerations here are a bit different.
 *    A partial path is one which can be executed in any number of workers in
 *    parallel such that each worker will generate a subset of the path's
 *    overall result.
 *
 *    As in add_path, the partial_pathlist is kept sorted with the cheapest
 *    total path in front.  This is depended on by multiple places, which
 *    just take the front entry as the cheapest path without searching.
 *
 *    We don't generate parameterized partial paths for several reasons.  Most
 *    importantly, they're not safe to execute, because there's nothing to
 *    make sure that a parallel scan within the parameterized portion of the
 *    plan is running with the same value in every worker at the same time.
 *    Fortunately, it seems unlikely to be worthwhile anyway, because having
 *    each worker scan the entire outer relation and a subset of the inner
 *    relation will generally be a terrible plan.  The inner (parameterized)
 *    side of the plan will be small anyway.  There could be rare cases where
 *    this wins big - e.g. if join order constraints put a 1-row relation on
 *    the outer side of the topmost join with a parameterized plan on the inner
 *    side - but we'll have to be content not to handle such cases until
 *    somebody builds an executor infrastructure that can cope with them.
 *
 *    Because we don't consider parameterized paths here, we also don't
 *    need to consider the row counts as a measure of quality: every path will
 *    produce the same number of rows.  Neither do we need to consider startup
 *    costs: parallelism is only used for plans that will be run to completion.
 *    Therefore, this routine is much simpler than add_path: it needs to
 *    consider only pathkeys and total cost.
 *
 *    As with add_path, we pfree paths that are found to be dominated by
 *    another partial path; this requires that there be no other references to
 *    such paths yet.  Hence, GatherPaths must not be created for a rel until
 *    we're done creating all partial paths for it.  Unlike add_path, we don't
 *    take an exception for IndexPaths as partial index paths won't be
 *    referenced by partial BitmapHeapPaths.
 */
void
add_partial_path(RelOptInfo *parent_rel, Path *new_path)
{
    bool        accept_new = true;  /* unless we find a superior old path */
    int         insert_at = 0;  /* where to insert new item */
    ListCell   *p1;

    /* Check for query cancel. */
    CHECK_FOR_INTERRUPTS();

    /* Path to be added must be parallel safe. */
    Assert(new_path->parallel_safe);

    /* Relation should be OK for parallelism, too. */
    Assert(parent_rel->consider_parallel);

    /*
     * As in add_path, throw out any paths which are dominated by the new
     * path, but throw out the new path if some existing path dominates it.
     */
    foreach(p1, parent_rel->partial_pathlist)
    {
        Path       *old_path = (Path *) lfirst(p1);
        bool        remove_old = false; /* unless new proves superior */
        PathKeysComparison keyscmp;

        /* Compare pathkeys. */
        keyscmp = compare_pathkeys(new_path->pathkeys, old_path->pathkeys);

        /* Unless pathkeys are incompatible, keep just one of the two paths. */
        if (keyscmp != PATHKEYS_DIFFERENT)
        {
            if (new_path->total_cost > old_path->total_cost * STD_FUZZ_FACTOR)
            {
                /* New path costs more; keep it only if pathkeys are better. */
                if (keyscmp != PATHKEYS_BETTER1)
                    accept_new = false;
            }
            else if (old_path->total_cost > new_path->total_cost
                     * STD_FUZZ_FACTOR)
            {
                /* Old path costs more; keep it only if pathkeys are better. */
                if (keyscmp != PATHKEYS_BETTER2)
                    remove_old = true;
            }
            else if (keyscmp == PATHKEYS_BETTER1)
            {
                /* Costs are about the same, new path has better pathkeys. */
                remove_old = true;
            }
            else if (keyscmp == PATHKEYS_BETTER2)
            {
                /* Costs are about the same, old path has better pathkeys. */
                accept_new = false;
            }
            else if (old_path->total_cost > new_path->total_cost * 1.0000000001)
            {
                /* Pathkeys are the same, and the old path costs more. */
                remove_old = true;
            }
            else
            {
                /*
                 * Pathkeys are the same, and new path isn't materially
                 * cheaper.
                 */
                accept_new = false;
            }
        }

        /*
         * Remove current element from partial_pathlist if dominated by new.
         */
        if (remove_old)
        {
            parent_rel->partial_pathlist =
                foreach_delete_current(parent_rel->partial_pathlist, p1);
            pfree(old_path);
        }
        else
        {
            /* new belongs after this old path if it has cost >= old's */
            if (new_path->total_cost >= old_path->total_cost)
                insert_at = foreach_current_index(p1) + 1;
        }

        /*
         * If we found an old path that dominates new_path, we can quit
         * scanning the partial_pathlist; we will not add new_path, and we
         * assume new_path cannot dominate any later path.
         */
        if (!accept_new)
            break;
    }

    if (accept_new)
    {
        /* Accept the new path: insert it at proper place */
        parent_rel->partial_pathlist =
            list_insert_nth(parent_rel->partial_pathlist, insert_at, new_path);
    }
    else
    {
        /* Reject and recycle the new path */
        pfree(new_path);
    }
}

/*
 * add_partial_path_precheck
 *    Check whether a proposed new partial path could possibly get accepted.
 *
 * Unlike add_path_precheck, we can ignore startup cost and parameterization,
 * since they don't matter for partial paths (see add_partial_path).  But
 * we do want to make sure we don't add a partial path if there's already
 * a complete path that dominates it, since in that case the proposed path
 * is surely a loser.
 */
bool
add_partial_path_precheck(RelOptInfo *parent_rel, Cost total_cost,
                          List *pathkeys)
{
    ListCell   *p1;

    /*
     * Our goal here is twofold.  First, we want to find out whether this path
     * is clearly inferior to some existing partial path.  If so, we want to
     * reject it immediately.  Second, we want to find out whether this path
     * is clearly superior to some existing partial path -- at least, modulo
     * final cost computations.  If so, we definitely want to consider it.
     *
     * Unlike add_path(), we always compare pathkeys here.  This is because we
     * expect partial_pathlist to be very short, and getting a definitive
     * answer at this stage avoids the need to call add_path_precheck.
     */
    foreach(p1, parent_rel->partial_pathlist)
    {
        Path       *old_path = (Path *) lfirst(p1);
        PathKeysComparison keyscmp;

        keyscmp = compare_pathkeys(pathkeys, old_path->pathkeys);
        if (keyscmp != PATHKEYS_DIFFERENT)
        {
            if (total_cost > old_path->total_cost * STD_FUZZ_FACTOR &&
                keyscmp != PATHKEYS_BETTER1)
                return false;
            if (old_path->total_cost > total_cost * STD_FUZZ_FACTOR &&
                keyscmp != PATHKEYS_BETTER2)
                return true;
        }
    }

    /*
     * This path is neither clearly inferior to an existing partial path nor
     * clearly good enough that it might replace one.  Compare it to
     * non-parallel plans.  If it loses even before accounting for the cost of
     * the Gather node, we should definitely reject it.
     *
     * Note that we pass the total_cost to add_path_precheck twice.  This is
     * because it's never advantageous to consider the startup cost of a
     * partial path; the resulting plans, if run in parallel, will be run to
     * completion.
     */
    if (!add_path_precheck(parent_rel, total_cost, total_cost, pathkeys,
                           NULL))
        return false;

    return true;
}


/*****************************************************************************
 *      PATH NODE CREATION ROUTINES
 *****************************************************************************/

/*
 * create_seqscan_path
 *    Creates a path corresponding to a sequential scan, returning the
 *    pathnode.
 */
Path *
create_seqscan_path(PlannerInfo *root, RelOptInfo *rel,
                    Relids required_outer, int parallel_workers)
{
    Path       *pathnode = makeNode(Path);

    pathnode->pathtype = T_SeqScan;
    pathnode->parent = rel;
    pathnode->pathtarget = rel->reltarget;
    pathnode->param_info = get_baserel_parampathinfo(root, rel,
                                                     required_outer);
    pathnode->parallel_aware = parallel_workers > 0 ? true : false;
    pathnode->parallel_safe = rel->consider_parallel;
    pathnode->parallel_workers = parallel_workers;
    pathnode->pathkeys = NIL;   /* seqscan has unordered result */

    cost_seqscan(pathnode, root, rel, pathnode->param_info);

    return pathnode;
}

/*
 * create_samplescan_path
 *    Creates a path node for a sampled table scan.
 */
Path *
create_samplescan_path(PlannerInfo *root, RelOptInfo *rel, Relids required_outer)
{
    Path       *pathnode = makeNode(Path);

    pathnode->pathtype = T_SampleScan;
    pathnode->parent = rel;
    pathnode->pathtarget = rel->reltarget;
    pathnode->param_info = get_baserel_parampathinfo(root, rel,
                                                     required_outer);
    pathnode->parallel_aware = false;
    pathnode->parallel_safe = rel->consider_parallel;
    pathnode->parallel_workers = 0;
    pathnode->pathkeys = NIL;   /* samplescan has unordered result */

    cost_samplescan(pathnode, root, rel, pathnode->param_info);

    return pathnode;
}

/*
 * create_index_path
 *    Creates a path node for an index scan.
 *
 * 'index' is a usable index.
 * 'indexclauses' is a list of IndexClause nodes representing clauses
 *          to be enforced as qual conditions in the scan.
 * 'indexorderbys' is a list of bare expressions (no RestrictInfos)
 *          to be used as index ordering operators in the scan.
 * 'indexorderbycols' is an integer list of index column numbers (zero based)
 *          the ordering operators can be used with.
 * 'pathkeys' describes the ordering of the path.
 * 'indexscandir' is ForwardScanDirection or BackwardScanDirection
 *          for an ordered index, or NoMovementScanDirection for
 *          an unordered index.
 * 'indexonly' is true if an index-only scan is wanted.
 * 'required_outer' is the set of outer relids for a parameterized path.
 * 'loop_count' is the number of repetitions of the indexscan to factor into
 *      estimates of caching behavior.
 * 'partial_path' is true if constructing a parallel index scan path.
 *
 * Returns the new path node.
 */
IndexPath *
create_index_path(PlannerInfo *root,
                  IndexOptInfo *index,
                  List *indexclauses,
                  List *indexorderbys,
                  List *indexorderbycols,
                  List *pathkeys,
                  ScanDirection indexscandir,
                  bool indexonly,
                  Relids required_outer,
                  double loop_count,
                  bool partial_path)
{
    IndexPath  *pathnode = makeNode(IndexPath);
    RelOptInfo *rel = index->rel;

    pathnode->path.pathtype = indexonly ? T_IndexOnlyScan : T_IndexScan;
    pathnode->path.parent = rel;
    pathnode->path.pathtarget = rel->reltarget;
    pathnode->path.param_info = get_baserel_parampathinfo(root, rel,
                                                          required_outer);
    pathnode->path.parallel_aware = false;
    pathnode->path.parallel_safe = rel->consider_parallel;
    pathnode->path.parallel_workers = 0;
    pathnode->path.pathkeys = pathkeys;

    pathnode->indexinfo = index;
    pathnode->indexclauses = indexclauses;
    pathnode->indexorderbys = indexorderbys;
    pathnode->indexorderbycols = indexorderbycols;
    pathnode->indexscandir = indexscandir;

    cost_index(pathnode, root, loop_count, partial_path);

    return pathnode;
}

/*
 * create_bitmap_heap_path
 *    Creates a path node for a bitmap scan.
 *
 * 'bitmapqual' is a tree of IndexPath, BitmapAndPath, and BitmapOrPath nodes.
 * 'required_outer' is the set of outer relids for a parameterized path.
 * 'loop_count' is the number of repetitions of the indexscan to factor into
 *      estimates of caching behavior.
 *
 * loop_count should match the value used when creating the component
 * IndexPaths.
 */
BitmapHeapPath *
create_bitmap_heap_path(PlannerInfo *root,
                        RelOptInfo *rel,
                        Path *bitmapqual,
                        Relids required_outer,
                        double loop_count,
                        int parallel_degree)
{
    BitmapHeapPath *pathnode = makeNode(BitmapHeapPath);

    pathnode->path.pathtype = T_BitmapHeapScan;
    pathnode->path.parent = rel;
    pathnode->path.pathtarget = rel->reltarget;
    pathnode->path.param_info = get_baserel_parampathinfo(root, rel,
                                                          required_outer);
    pathnode->path.parallel_aware = parallel_degree > 0 ? true : false;
    pathnode->path.parallel_safe = rel->consider_parallel;
    pathnode->path.parallel_workers = parallel_degree;
    pathnode->path.pathkeys = NIL;  /* always unordered */

    pathnode->bitmapqual = bitmapqual;

    cost_bitmap_heap_scan(&pathnode->path, root, rel,
                          pathnode->path.param_info,
                          bitmapqual, loop_count);

    return pathnode;
}

/*
 * create_bitmap_and_path
 *    Creates a path node representing a BitmapAnd.
 */
BitmapAndPath *
create_bitmap_and_path(PlannerInfo *root,
                       RelOptInfo *rel,
                       List *bitmapquals)
{
    BitmapAndPath *pathnode = makeNode(BitmapAndPath);
    Relids      required_outer = NULL;
    ListCell   *lc;

    pathnode->path.pathtype = T_BitmapAnd;
    pathnode->path.parent = rel;
    pathnode->path.pathtarget = rel->reltarget;

    /*
     * Identify the required outer rels as the union of what the child paths
     * depend on.  (Alternatively, we could insist that the caller pass this
     * in, but it's more convenient and reliable to compute it here.)
     */
    foreach(lc, bitmapquals)
    {
        Path       *bitmapqual = (Path *) lfirst(lc);

        required_outer = bms_add_members(required_outer,
                                         PATH_REQ_OUTER(bitmapqual));
    }
    pathnode->path.param_info = get_baserel_parampathinfo(root, rel,
                                                          required_outer);

    /*
     * Currently, a BitmapHeapPath, BitmapAndPath, or BitmapOrPath will be
     * parallel-safe if and only if rel->consider_parallel is set.  So, we can
     * set the flag for this path based only on the relation-level flag,
     * without actually iterating over the list of children.
     */
    pathnode->path.parallel_aware = false;
    pathnode->path.parallel_safe = rel->consider_parallel;
    pathnode->path.parallel_workers = 0;

    pathnode->path.pathkeys = NIL;  /* always unordered */

    pathnode->bitmapquals = bitmapquals;

    /* this sets bitmapselectivity as well as the regular cost fields: */
    cost_bitmap_and_node(pathnode, root);

    return pathnode;
}

/*
 * create_bitmap_or_path
 *    Creates a path node representing a BitmapOr.
 */
BitmapOrPath *
create_bitmap_or_path(PlannerInfo *root,
                      RelOptInfo *rel,
                      List *bitmapquals)
{
    BitmapOrPath *pathnode = makeNode(BitmapOrPath);
    Relids      required_outer = NULL;
    ListCell   *lc;

    pathnode->path.pathtype = T_BitmapOr;
    pathnode->path.parent = rel;
    pathnode->path.pathtarget = rel->reltarget;

    /*
     * Identify the required outer rels as the union of what the child paths
     * depend on.  (Alternatively, we could insist that the caller pass this
     * in, but it's more convenient and reliable to compute it here.)
     */
    foreach(lc, bitmapquals)
    {
        Path       *bitmapqual = (Path *) lfirst(lc);

        required_outer = bms_add_members(required_outer,
                                         PATH_REQ_OUTER(bitmapqual));
    }
    pathnode->path.param_info = get_baserel_parampathinfo(root, rel,
                                                          required_outer);

    /*
     * Currently, a BitmapHeapPath, BitmapAndPath, or BitmapOrPath will be
     * parallel-safe if and only if rel->consider_parallel is set.  So, we can
     * set the flag for this path based only on the relation-level flag,
     * without actually iterating over the list of children.
     */
    pathnode->path.parallel_aware = false;
    pathnode->path.parallel_safe = rel->consider_parallel;
    pathnode->path.parallel_workers = 0;

    pathnode->path.pathkeys = NIL;  /* always unordered */

    pathnode->bitmapquals = bitmapquals;

    /* this sets bitmapselectivity as well as the regular cost fields: */
    cost_bitmap_or_node(pathnode, root);

    return pathnode;
}

/*
 * create_tidscan_path
 *    Creates a path corresponding to a scan by TID, returning the pathnode.
 */
TidPath *
create_tidscan_path(PlannerInfo *root, RelOptInfo *rel, List *tidquals,
                    Relids required_outer)
{
    TidPath    *pathnode = makeNode(TidPath);

    pathnode->path.pathtype = T_TidScan;
    pathnode->path.parent = rel;
    pathnode->path.pathtarget = rel->reltarget;
    pathnode->path.param_info = get_baserel_parampathinfo(root, rel,
                                                          required_outer);
    pathnode->path.parallel_aware = false;
    pathnode->path.parallel_safe = rel->consider_parallel;
    pathnode->path.parallel_workers = 0;
    pathnode->path.pathkeys = NIL;  /* always unordered */

    pathnode->tidquals = tidquals;

    cost_tidscan(&pathnode->path, root, rel, tidquals,
                 pathnode->path.param_info);

    return pathnode;
}

/*
 * create_append_path
 *    Creates a path corresponding to an Append plan, returning the
 *    pathnode.
 *
 * Note that we must handle subpaths = NIL, representing a dummy access path.
 * Also, there are callers that pass root = NULL.
 */
AppendPath *
create_append_path(PlannerInfo *root,
                   RelOptInfo *rel,
                   List *subpaths, List *partial_subpaths,
                   List *pathkeys, Relids required_outer,
                   int parallel_workers, bool parallel_aware,
                   List *partitioned_rels, double rows)
{
    AppendPath *pathnode = makeNode(AppendPath);
    ListCell   *l;

    Assert(!parallel_aware || parallel_workers > 0);

    pathnode->path.pathtype = T_Append;
    pathnode->path.parent = rel;
    pathnode->path.pathtarget = rel->reltarget;

    /*
     * When generating an Append path for a partitioned table, there may be
     * parameters that are useful so we can eliminate certain partitions
     * during execution.  Here we'll go all the way and fully populate the
     * parameter info data as we do for normal base relations.  However, we
     * need only bother doing this for RELOPT_BASEREL rels, as
     * RELOPT_OTHER_MEMBER_REL's Append paths are merged into the base rel's
     * Append subpaths.  It would do no harm to do this, we just avoid it to
     * save wasting effort.
     */
    if (partitioned_rels != NIL && root && rel->reloptkind == RELOPT_BASEREL)
        pathnode->path.param_info = get_baserel_parampathinfo(root,
                                                              rel,
                                                              required_outer);
    else
        pathnode->path.param_info = get_appendrel_parampathinfo(rel,
                                                                required_outer);

    pathnode->path.parallel_aware = parallel_aware;
    pathnode->path.parallel_safe = rel->consider_parallel;
    pathnode->path.parallel_workers = parallel_workers;
    pathnode->path.pathkeys = pathkeys;
    pathnode->partitioned_rels = list_copy(partitioned_rels);

    /*
     * For parallel append, non-partial paths are sorted by descending total
     * costs. That way, the total time to finish all non-partial paths is
     * minimized.  Also, the partial paths are sorted by descending startup
     * costs.  There may be some paths that require to do startup work by a
     * single worker.  In such case, it's better for workers to choose the
     * expensive ones first, whereas the leader should choose the cheapest
     * startup plan.
     */
    if (pathnode->path.parallel_aware)
    {
        /*
         * We mustn't fiddle with the order of subpaths when the Append has
         * pathkeys.  The order they're listed in is critical to keeping the
         * pathkeys valid.
         */
        Assert(pathkeys == NIL);

        list_sort(subpaths, append_total_cost_compare);
        list_sort(partial_subpaths, append_startup_cost_compare);
    }
    pathnode->first_partial_path = list_length(subpaths);
    pathnode->subpaths = list_concat(subpaths, partial_subpaths);

    /*
     * Apply query-wide LIMIT if known and path is for sole base relation.
     * (Handling this at this low level is a bit klugy.)
     */
    if (root != NULL && bms_equal(rel->relids, root->all_baserels))
        pathnode->limit_tuples = root->limit_tuples;
    else
        pathnode->limit_tuples = -1.0;

    foreach(l, pathnode->subpaths)
    {
        Path       *subpath = (Path *) lfirst(l);

        pathnode->path.parallel_safe = pathnode->path.parallel_safe &&
            subpath->parallel_safe;

        /* All child paths must have same parameterization */
        Assert(bms_equal(PATH_REQ_OUTER(subpath), required_outer));
    }

    Assert(!parallel_aware || pathnode->path.parallel_safe);

    /*
     * If there's exactly one child path, the Append is a no-op and will be
     * discarded later (in setrefs.c); therefore, we can inherit the child's
     * size and cost, as well as its pathkeys if any (overriding whatever the
     * caller might've said).  Otherwise, we must do the normal costsize
     * calculation.
     */
    if (list_length(pathnode->subpaths) == 1)
    {
        Path       *child = (Path *) linitial(pathnode->subpaths);

        pathnode->path.rows = child->rows;
        pathnode->path.startup_cost = child->startup_cost;
        pathnode->path.total_cost = child->total_cost;
        pathnode->path.pathkeys = child->pathkeys;
    }
    else
        cost_append(pathnode);

    /* If the caller provided a row estimate, override the computed value. */
    if (rows >= 0)
        pathnode->path.rows = rows;

    return pathnode;
}

/*
 * append_total_cost_compare
 *    list_sort comparator for sorting append child paths
 *    by total_cost descending
 *
 * For equal total costs, we fall back to comparing startup costs; if those
 * are equal too, break ties using bms_compare on the paths' relids.
 * (This is to avoid getting unpredictable results from list_sort.)
 */
static int
append_total_cost_compare(const ListCell *a, const ListCell *b)
{
    Path       *path1 = (Path *) lfirst(a);
    Path       *path2 = (Path *) lfirst(b);
    int         cmp;

    cmp = compare_path_costs(path1, path2, TOTAL_COST);
    if (cmp != 0)
        return -cmp;
    return bms_compare(path1->parent->relids, path2->parent->relids);
}

/*
 * append_startup_cost_compare
 *    list_sort comparator for sorting append child paths
 *    by startup_cost descending
 *
 * For equal startup costs, we fall back to comparing total costs; if those
 * are equal too, break ties using bms_compare on the paths' relids.
 * (This is to avoid getting unpredictable results from list_sort.)
 */
static int
append_startup_cost_compare(const ListCell *a, const ListCell *b)
{
    Path       *path1 = (Path *) lfirst(a);
    Path       *path2 = (Path *) lfirst(b);
    int         cmp;

    cmp = compare_path_costs(path1, path2, STARTUP_COST);
    if (cmp != 0)
        return -cmp;
    return bms_compare(path1->parent->relids, path2->parent->relids);
}

/*
 * create_merge_append_path
 *    Creates a path corresponding to a MergeAppend plan, returning the
 *    pathnode.
 */
MergeAppendPath *
create_merge_append_path(PlannerInfo *root,
                         RelOptInfo *rel,
                         List *subpaths,
                         List *pathkeys,
                         Relids required_outer,
                         List *partitioned_rels)
{
    MergeAppendPath *pathnode = makeNode(MergeAppendPath);
    Cost        input_startup_cost;
    Cost        input_total_cost;
    ListCell   *l;

    pathnode->path.pathtype = T_MergeAppend;
    pathnode->path.parent = rel;
    pathnode->path.pathtarget = rel->reltarget;
    pathnode->path.param_info = get_appendrel_parampathinfo(rel,
                                                            required_outer);
    pathnode->path.parallel_aware = false;
    pathnode->path.parallel_safe = rel->consider_parallel;
    pathnode->path.parallel_workers = 0;
    pathnode->path.pathkeys = pathkeys;
    pathnode->partitioned_rels = list_copy(partitioned_rels);
    pathnode->subpaths = subpaths;

    /*
     * Apply query-wide LIMIT if known and path is for sole base relation.
     * (Handling this at this low level is a bit klugy.)
     */
    if (bms_equal(rel->relids, root->all_baserels))
        pathnode->limit_tuples = root->limit_tuples;
    else
        pathnode->limit_tuples = -1.0;

    /*
     * Add up the sizes and costs of the input paths.
     */
    pathnode->path.rows = 0;
    input_startup_cost = 0;
    input_total_cost = 0;
    foreach(l, subpaths)
    {
        Path       *subpath = (Path *) lfirst(l);

        pathnode->path.rows += subpath->rows;
        pathnode->path.parallel_safe = pathnode->path.parallel_safe &&
            subpath->parallel_safe;

        if (pathkeys_contained_in(pathkeys, subpath->pathkeys))
        {
            /* Subpath is adequately ordered, we won't need to sort it */
            input_startup_cost += subpath->startup_cost;
            input_total_cost += subpath->total_cost;
        }
        else
        {
            /* We'll need to insert a Sort node, so include cost for that */
            Path        sort_path;  /* dummy for result of cost_sort */

            cost_sort(&sort_path,
                      root,
                      pathkeys,
                      subpath->total_cost,
                      subpath->parent->tuples,
                      subpath->pathtarget->width,
                      0.0,
                      work_mem,
                      pathnode->limit_tuples);
            input_startup_cost += sort_path.startup_cost;
            input_total_cost += sort_path.total_cost;
        }

        /* All child paths must have same parameterization */
        Assert(bms_equal(PATH_REQ_OUTER(subpath), required_outer));
    }

    /*
     * Now we can compute total costs of the MergeAppend.  If there's exactly
     * one child path, the MergeAppend is a no-op and will be discarded later
     * (in setrefs.c); otherwise we do the normal cost calculation.
     */
    if (list_length(subpaths) == 1)
    {
        pathnode->path.startup_cost = input_startup_cost;
        pathnode->path.total_cost = input_total_cost;
    }
    else
        cost_merge_append(&pathnode->path, root,
                          pathkeys, list_length(subpaths),
                          input_startup_cost, input_total_cost,
                          pathnode->path.rows);

    return pathnode;
}

/*
 * create_group_result_path
 *    Creates a path representing a Result-and-nothing-else plan.
 *
 * This is only used for degenerate grouping cases, in which we know we
 * need to produce one result row, possibly filtered by a HAVING qual.
 */
GroupResultPath *
create_group_result_path(PlannerInfo *root, RelOptInfo *rel,
                         PathTarget *target, List *havingqual)
{
    GroupResultPath *pathnode = makeNode(GroupResultPath);

    pathnode->path.pathtype = T_Result;
    pathnode->path.parent = rel;
    pathnode->path.pathtarget = target;
    pathnode->path.param_info = NULL;   /* there are no other rels... */
    pathnode->path.parallel_aware = false;
    pathnode->path.parallel_safe = rel->consider_parallel;
    pathnode->path.parallel_workers = 0;
    pathnode->path.pathkeys = NIL;
    pathnode->quals = havingqual;

    /*
     * We can't quite use cost_resultscan() because the quals we want to
     * account for are not baserestrict quals of the rel.  Might as well just
     * hack it here.
     */
    pathnode->path.rows = 1;
    pathnode->path.startup_cost = target->cost.startup;
    pathnode->path.total_cost = target->cost.startup +
        cpu_tuple_cost + target->cost.per_tuple;

    /*
     * Add cost of qual, if any --- but we ignore its selectivity, since our
     * rowcount estimate should be 1 no matter what the qual is.
     */
    if (havingqual)
    {
        QualCost    qual_cost;

        cost_qual_eval(&qual_cost, havingqual, root);
        /* havingqual is evaluated once at startup */
        pathnode->path.startup_cost += qual_cost.startup + qual_cost.per_tuple;
        pathnode->path.total_cost += qual_cost.startup + qual_cost.per_tuple;
    }

    return pathnode;
}

/*
 * create_material_path
 *    Creates a path corresponding to a Material plan, returning the
 *    pathnode.
 */
MaterialPath *
create_material_path(RelOptInfo *rel, Path *subpath)
{
    MaterialPath *pathnode = makeNode(MaterialPath);

    Assert(subpath->parent == rel);

    pathnode->path.pathtype = T_Material;
    pathnode->path.parent = rel;
    pathnode->path.pathtarget = rel->reltarget;
    pathnode->path.param_info = subpath->param_info;
    pathnode->path.parallel_aware = false;
    pathnode->path.parallel_safe = rel->consider_parallel &&
        subpath->parallel_safe;
    pathnode->path.parallel_workers = subpath->parallel_workers;
    pathnode->path.pathkeys = subpath->pathkeys;

    pathnode->subpath = subpath;

    cost_material(&pathnode->path,
                  subpath->startup_cost,
                  subpath->total_cost,
                  subpath->rows,
                  subpath->pathtarget->width);

    return pathnode;
}

/*
 * create_unique_path
 *    Creates a path representing elimination of distinct rows from the
 *    input data.  Distinct-ness is defined according to the needs of the
 *    semijoin represented by sjinfo.  If it is not possible to identify
 *    how to make the data unique, NULL is returned.
 *
 * If used at all, this is likely to be called repeatedly on the same rel;
 * and the input subpath should always be the same (the cheapest_total path
 * for the rel).  So we cache the result.
 */
UniquePath *
create_unique_path(PlannerInfo *root, RelOptInfo *rel, Path *subpath,
                   SpecialJoinInfo *sjinfo)
{
    UniquePath *pathnode;
    Path        sort_path;      /* dummy for result of cost_sort */
    Path        agg_path;       /* dummy for result of cost_agg */
    MemoryContext oldcontext;
    int         numCols;

    /* Caller made a mistake if subpath isn't cheapest_total ... */
    Assert(subpath == rel->cheapest_total_path);
    Assert(subpath->parent == rel);
    /* ... or if SpecialJoinInfo is the wrong one */
    Assert(sjinfo->jointype == JOIN_SEMI);
    Assert(bms_equal(rel->relids, sjinfo->syn_righthand));

    /* If result already cached, return it */
    if (rel->cheapest_unique_path)
        return (UniquePath *) rel->cheapest_unique_path;

    /* If it's not possible to unique-ify, return NULL */
    if (!(sjinfo->semi_can_btree || sjinfo->semi_can_hash))
        return NULL;

    /*
     * When called during GEQO join planning, we are in a short-lived memory
     * context.  We must make sure that the path and any subsidiary data
     * structures created for a baserel survive the GEQO cycle, else the
     * baserel is trashed for future GEQO cycles.  On the other hand, when we
     * are creating those for a joinrel during GEQO, we don't want them to
     * clutter the main planning context.  Upshot is that the best solution is
     * to explicitly allocate memory in the same context the given RelOptInfo
     * is in.
     */
    oldcontext = MemoryContextSwitchTo(GetMemoryChunkContext(rel));

    pathnode = makeNode(UniquePath);

    pathnode->path.pathtype = T_Unique;
    pathnode->path.parent = rel;
    pathnode->path.pathtarget = rel->reltarget;
    pathnode->path.param_info = subpath->param_info;
    pathnode->path.parallel_aware = false;
    pathnode->path.parallel_safe = rel->consider_parallel &&
        subpath->parallel_safe;
    pathnode->path.parallel_workers = subpath->parallel_workers;

    /*
     * Assume the output is unsorted, since we don't necessarily have pathkeys
     * to represent it.  (This might get overridden below.)
     */
    pathnode->path.pathkeys = NIL;

    pathnode->subpath = subpath;
    pathnode->in_operators = sjinfo->semi_operators;
    pathnode->uniq_exprs = sjinfo->semi_rhs_exprs;

    /*
     * If the input is a relation and it has a unique index that proves the
     * semi_rhs_exprs are unique, then we don't need to do anything.  Note
     * that relation_has_unique_index_for automatically considers restriction
     * clauses for the rel, as well.
     */
    if (rel->rtekind == RTE_RELATION && sjinfo->semi_can_btree &&
        relation_has_unique_index_for(root, rel, NIL,
                                      sjinfo->semi_rhs_exprs,
                                      sjinfo->semi_operators))
    {
        pathnode->umethod = UNIQUE_PATH_NOOP;
        pathnode->path.rows = rel->rows;
        pathnode->path.startup_cost = subpath->startup_cost;
        pathnode->path.total_cost = subpath->total_cost;
        pathnode->path.pathkeys = subpath->pathkeys;

        rel->cheapest_unique_path = (Path *) pathnode;

        MemoryContextSwitchTo(oldcontext);

        return pathnode;
    }

    /*
     * If the input is a subquery whose output must be unique already, then we
     * don't need to do anything.  The test for uniqueness has to consider
     * exactly which columns we are extracting; for example "SELECT DISTINCT
     * x,y" doesn't guarantee that x alone is distinct. So we cannot check for
     * this optimization unless semi_rhs_exprs consists only of simple Vars
     * referencing subquery outputs.  (Possibly we could do something with
     * expressions in the subquery outputs, too, but for now keep it simple.)
     */
    if (rel->rtekind == RTE_SUBQUERY)
    {
        RangeTblEntry *rte = planner_rt_fetch(rel->relid, root);

        if (query_supports_distinctness(rte->subquery))
        {
            List       *sub_tlist_colnos;

            sub_tlist_colnos = translate_sub_tlist(sjinfo->semi_rhs_exprs,
                                                   rel->relid);

            if (sub_tlist_colnos &&
                query_is_distinct_for(rte->subquery,
                                      sub_tlist_colnos,
                                      sjinfo->semi_operators))
            {
                pathnode->umethod = UNIQUE_PATH_NOOP;
                pathnode->path.rows = rel->rows;
                pathnode->path.startup_cost = subpath->startup_cost;
                pathnode->path.total_cost = subpath->total_cost;
                pathnode->path.pathkeys = subpath->pathkeys;

                rel->cheapest_unique_path = (Path *) pathnode;

                MemoryContextSwitchTo(oldcontext);

                return pathnode;
            }
        }
    }

    /* Estimate number of output rows */
    pathnode->path.rows = estimate_num_groups(root,
                                              sjinfo->semi_rhs_exprs,
                                              rel->rows,
                                              NULL);
    numCols = list_length(sjinfo->semi_rhs_exprs);

    if (sjinfo->semi_can_btree)
    {
        /*
         * Estimate cost for sort+unique implementation
         */
        cost_sort(&sort_path, root, NIL,
                  subpath->total_cost,
                  rel->rows,
                  subpath->pathtarget->width,
                  0.0,
                  work_mem,
                  -1.0);

        /*
         * Charge one cpu_operator_cost per comparison per input tuple. We
         * assume all columns get compared at most of the tuples. (XXX
         * probably this is an overestimate.)  This should agree with
         * create_upper_unique_path.
         */
        sort_path.total_cost += cpu_operator_cost * rel->rows * numCols;
    }

    if (sjinfo->semi_can_hash)
    {
        /*
         * Estimate the overhead per hashtable entry at 64 bytes (same as in
         * planner.c).
         */
        int         hashentrysize = subpath->pathtarget->width + 64;
        int         hash_mem = get_hash_mem();

        if (hashentrysize * pathnode->path.rows > hash_mem * 1024L)
        {
            /*
             * We should not try to hash.  Hack the SpecialJoinInfo to
             * remember this, in case we come through here again.
             */
            sjinfo->semi_can_hash = false;
        }
        else
            cost_agg(&agg_path, root,
                     AGG_HASHED, NULL,
                     numCols, pathnode->path.rows,
                     NIL,
                     subpath->startup_cost,
                     subpath->total_cost,
                     rel->rows,
                     subpath->pathtarget->width);
    }

    if (sjinfo->semi_can_btree && sjinfo->semi_can_hash)
    {
        if (agg_path.total_cost < sort_path.total_cost)
            pathnode->umethod = UNIQUE_PATH_HASH;
        else
            pathnode->umethod = UNIQUE_PATH_SORT;
    }
    else if (sjinfo->semi_can_btree)
        pathnode->umethod = UNIQUE_PATH_SORT;
    else if (sjinfo->semi_can_hash)
        pathnode->umethod = UNIQUE_PATH_HASH;
    else
    {
        /* we can get here only if we abandoned hashing above */
        MemoryContextSwitchTo(oldcontext);
        return NULL;
    }

    if (pathnode->umethod == UNIQUE_PATH_HASH)
    {
        pathnode->path.startup_cost = agg_path.startup_cost;
        pathnode->path.total_cost = agg_path.total_cost;
    }
    else
    {
        pathnode->path.startup_cost = sort_path.startup_cost;
        pathnode->path.total_cost = sort_path.total_cost;
    }

    rel->cheapest_unique_path = (Path *) pathnode;

    MemoryContextSwitchTo(oldcontext);

    return pathnode;
}

/*
 * create_gather_merge_path
 *
 *    Creates a path corresponding to a gather merge scan, returning
 *    the pathnode.
 */
GatherMergePath *
create_gather_merge_path(PlannerInfo *root, RelOptInfo *rel, Path *subpath,
                         PathTarget *target, List *pathkeys,
                         Relids required_outer, double *rows)
{
    GatherMergePath *pathnode = makeNode(GatherMergePath);
    Cost        input_startup_cost = 0;
    Cost        input_total_cost = 0;

    Assert(subpath->parallel_safe);
    Assert(pathkeys);

    pathnode->path.pathtype = T_GatherMerge;
    pathnode->path.parent = rel;
    pathnode->path.param_info = get_baserel_parampathinfo(root, rel,
                                                          required_outer);
    pathnode->path.parallel_aware = false;

    pathnode->subpath = subpath;
    pathnode->num_workers = subpath->parallel_workers;
    pathnode->path.pathkeys = pathkeys;
    pathnode->path.pathtarget = target ? target : rel->reltarget;
    pathnode->path.rows += subpath->rows;

    if (pathkeys_contained_in(pathkeys, subpath->pathkeys))
    {
        /* Subpath is adequately ordered, we won't need to sort it */
        input_startup_cost += subpath->startup_cost;
        input_total_cost += subpath->total_cost;
    }
    else
    {
        /* We'll need to insert a Sort node, so include cost for that */
        Path        sort_path;  /* dummy for result of cost_sort */

        cost_sort(&sort_path,
                  root,
                  pathkeys,
                  subpath->total_cost,
                  subpath->rows,
                  subpath->pathtarget->width,
                  0.0,
                  work_mem,
                  -1);
        input_startup_cost += sort_path.startup_cost;
        input_total_cost += sort_path.total_cost;
    }

    cost_gather_merge(pathnode, root, rel, pathnode->path.param_info,
                      input_startup_cost, input_total_cost, rows);

    return pathnode;
}

/*
 * translate_sub_tlist - get subquery column numbers represented by tlist
 *
 * The given targetlist usually contains only Vars referencing the given relid.
 * Extract their varattnos (ie, the column numbers of the subquery) and return
 * as an integer List.
 *
 * If any of the tlist items is not a simple Var, we cannot determine whether
 * the subquery's uniqueness condition (if any) matches ours, so punt and
 * return NIL.
 */
static List *
translate_sub_tlist(List *tlist, int relid)
{
    List       *result = NIL;
    ListCell   *l;

    foreach(l, tlist)
    {
        Var        *var = (Var *) lfirst(l);

        if (!var || !IsA(var, Var) ||
            var->varno != relid)
            return NIL;         /* punt */

        result = lappend_int(result, var->varattno);
    }
    return result;
}

/*
 * create_gather_path
 *    Creates a path corresponding to a gather scan, returning the
 *    pathnode.
 *
 * 'rows' may optionally be set to override row estimates from other sources.
 */
GatherPath *
create_gather_path(PlannerInfo *root, RelOptInfo *rel, Path *subpath,
                   PathTarget *target, Relids required_outer, double *rows)
{
    GatherPath *pathnode = makeNode(GatherPath);

    Assert(subpath->parallel_safe);

    pathnode->path.pathtype = T_Gather;
    pathnode->path.parent = rel;
    pathnode->path.pathtarget = target;
    pathnode->path.param_info = get_baserel_parampathinfo(root, rel,
                                                          required_outer);
    pathnode->path.parallel_aware = false;
    pathnode->path.parallel_safe = false;
    pathnode->path.parallel_workers = 0;
    pathnode->path.pathkeys = NIL;  /* Gather has unordered result */

    pathnode->subpath = subpath;
    pathnode->num_workers = subpath->parallel_workers;
    pathnode->single_copy = false;

    if (pathnode->num_workers == 0)
    {
        pathnode->path.pathkeys = subpath->pathkeys;
        pathnode->num_workers = 1;
        pathnode->single_copy = true;
    }

    cost_gather(pathnode, root, rel, pathnode->path.param_info, rows);

    return pathnode;
}

/*
 * create_subqueryscan_path
 *    Creates a path corresponding to a scan of a subquery,
 *    returning the pathnode.
 */
SubqueryScanPath *
create_subqueryscan_path(PlannerInfo *root, RelOptInfo *rel, Path *subpath,
                         List *pathkeys, Relids required_outer)
{
    SubqueryScanPath *pathnode = makeNode(SubqueryScanPath);

    pathnode->path.pathtype = T_SubqueryScan;
    pathnode->path.parent = rel;
    pathnode->path.pathtarget = rel->reltarget;
    pathnode->path.param_info = get_baserel_parampathinfo(root, rel,
                                                          required_outer);
    pathnode->path.parallel_aware = false;
    pathnode->path.parallel_safe = rel->consider_parallel &&
        subpath->parallel_safe;
    pathnode->path.parallel_workers = subpath->parallel_workers;
    pathnode->path.pathkeys = pathkeys;
    pathnode->subpath = subpath;

    cost_subqueryscan(pathnode, root, rel, pathnode->path.param_info);

    return pathnode;
}

/*
 * create_functionscan_path
 *    Creates a path corresponding to a sequential scan of a function,
 *    returning the pathnode.
 */
Path *
create_functionscan_path(PlannerInfo *root, RelOptInfo *rel,
                         List *pathkeys, Relids required_outer)
{
    Path       *pathnode = makeNode(Path);

    pathnode->pathtype = T_FunctionScan;
    pathnode->parent = rel;
    pathnode->pathtarget = rel->reltarget;
    pathnode->param_info = get_baserel_parampathinfo(root, rel,
                                                     required_outer);
    pathnode->parallel_aware = false;
    pathnode->parallel_safe = rel->consider_parallel;
    pathnode->parallel_workers = 0;
    pathnode->pathkeys = pathkeys;

    cost_functionscan(pathnode, root, rel, pathnode->param_info);

    return pathnode;
}

/*
 * create_tablefuncscan_path
 *    Creates a path corresponding to a sequential scan of a table function,
 *    returning the pathnode.
 */
Path *
create_tablefuncscan_path(PlannerInfo *root, RelOptInfo *rel,
                          Relids required_outer)
{
    Path       *pathnode = makeNode(Path);

    pathnode->pathtype = T_TableFuncScan;
    pathnode->parent = rel;
    pathnode->pathtarget = rel->reltarget;
    pathnode->param_info = get_baserel_parampathinfo(root, rel,
                                                     required_outer);
    pathnode->parallel_aware = false;
    pathnode->parallel_safe = rel->consider_parallel;
    pathnode->parallel_workers = 0;
    pathnode->pathkeys = NIL;   /* result is always unordered */

    cost_tablefuncscan(pathnode, root, rel, pathnode->param_info);

    return pathnode;
}

/*
 * create_valuesscan_path
 *    Creates a path corresponding to a scan of a VALUES list,
 *    returning the pathnode.
 */
Path *
create_valuesscan_path(PlannerInfo *root, RelOptInfo *rel,
                       Relids required_outer)
{
    Path       *pathnode = makeNode(Path);

    pathnode->pathtype = T_ValuesScan;
    pathnode->parent = rel;
    pathnode->pathtarget = rel->reltarget;
    pathnode->param_info = get_baserel_parampathinfo(root, rel,
                                                     required_outer);
    pathnode->parallel_aware = false;
    pathnode->parallel_safe = rel->consider_parallel;
    pathnode->parallel_workers = 0;
    pathnode->pathkeys = NIL;   /* result is always unordered */

    cost_valuesscan(pathnode, root, rel, pathnode->param_info);

    return pathnode;
}

/*
 * create_ctescan_path
 *    Creates a path corresponding to a scan of a non-self-reference CTE,
 *    returning the pathnode.
 */
Path *
create_ctescan_path(PlannerInfo *root, RelOptInfo *rel, Relids required_outer)
{
    Path       *pathnode = makeNode(Path);

    pathnode->pathtype = T_CteScan;
    pathnode->parent = rel;
    pathnode->pathtarget = rel->reltarget;
    pathnode->param_info = get_baserel_parampathinfo(root, rel,
                                                     required_outer);
    pathnode->parallel_aware = false;
    pathnode->parallel_safe = rel->consider_parallel;
    pathnode->parallel_workers = 0;
    pathnode->pathkeys = NIL;   /* XXX for now, result is always unordered */

    cost_ctescan(pathnode, root, rel, pathnode->param_info);

    return pathnode;
}

/*
 * create_namedtuplestorescan_path
 *    Creates a path corresponding to a scan of a named tuplestore, returning
 *    the pathnode.
 */
Path *
create_namedtuplestorescan_path(PlannerInfo *root, RelOptInfo *rel,
                                Relids required_outer)
{
    Path       *pathnode = makeNode(Path);

    pathnode->pathtype = T_NamedTuplestoreScan;
    pathnode->parent = rel;
    pathnode->pathtarget = rel->reltarget;
    pathnode->param_info = get_baserel_parampathinfo(root, rel,
                                                     required_outer);
    pathnode->parallel_aware = false;
    pathnode->parallel_safe = rel->consider_parallel;
    pathnode->parallel_workers = 0;
    pathnode->pathkeys = NIL;   /* result is always unordered */

    cost_namedtuplestorescan(pathnode, root, rel, pathnode->param_info);

    return pathnode;
}

/*
 * create_resultscan_path
 *    Creates a path corresponding to a scan of an RTE_RESULT relation,
 *    returning the pathnode.
 */
Path *
create_resultscan_path(PlannerInfo *root, RelOptInfo *rel,
                       Relids required_outer)
{
    Path       *pathnode = makeNode(Path);

    pathnode->pathtype = T_Result;
    pathnode->parent = rel;
    pathnode->pathtarget = rel->reltarget;
    pathnode->param_info = get_baserel_parampathinfo(root, rel,
                                                     required_outer);
    pathnode->parallel_aware = false;
    pathnode->parallel_safe = rel->consider_parallel;
    pathnode->parallel_workers = 0;
    pathnode->pathkeys = NIL;   /* result is always unordered */

    cost_resultscan(pathnode, root, rel, pathnode->param_info);

    return pathnode;
}

/*
 * create_worktablescan_path
 *    Creates a path corresponding to a scan of a self-reference CTE,
 *    returning the pathnode.
 */
Path *
create_worktablescan_path(PlannerInfo *root, RelOptInfo *rel,
                          Relids required_outer)
{
    Path       *pathnode = makeNode(Path);

    pathnode->pathtype = T_WorkTableScan;
    pathnode->parent = rel;
    pathnode->pathtarget = rel->reltarget;
    pathnode->param_info = get_baserel_parampathinfo(root, rel,
                                                     required_outer);
    pathnode->parallel_aware = false;
    pathnode->parallel_safe = rel->consider_parallel;
    pathnode->parallel_workers = 0;
    pathnode->pathkeys = NIL;   /* result is always unordered */

    /* Cost is the same as for a regular CTE scan */
    cost_ctescan(pathnode, root, rel, pathnode->param_info);

    return pathnode;
}

/*
 * create_foreignscan_path
 *    Creates a path corresponding to a scan of a foreign base table,
 *    returning the pathnode.
 *
 * This function is never called from core Postgres; rather, it's expected
 * to be called by the GetForeignPaths function of a foreign data wrapper.
 * We make the FDW supply all fields of the path, since we do not have any way
 * to calculate them in core.  However, there is a usually-sane default for
 * the pathtarget (rel->reltarget), so we let a NULL for "target" select that.
 */
ForeignPath *
create_foreignscan_path(PlannerInfo *root, RelOptInfo *rel,
                        PathTarget *target,
                        double rows, Cost startup_cost, Cost total_cost,
                        List *pathkeys,
                        Relids required_outer,
                        Path *fdw_outerpath,
                        List *fdw_private)
{
    ForeignPath *pathnode = makeNode(ForeignPath);

    /* Historically some FDWs were confused about when to use this */
    Assert(IS_SIMPLE_REL(rel));

    pathnode->path.pathtype = T_ForeignScan;
    pathnode->path.parent = rel;
    pathnode->path.pathtarget = target ? target : rel->reltarget;
    pathnode->path.param_info = get_baserel_parampathinfo(root, rel,
                                                          required_outer);
    pathnode->path.parallel_aware = false;
    pathnode->path.parallel_safe = rel->consider_parallel;
    pathnode->path.parallel_workers = 0;
    pathnode->path.rows = rows;
    pathnode->path.startup_cost = startup_cost;
    pathnode->path.total_cost = total_cost;
    pathnode->path.pathkeys = pathkeys;

    pathnode->fdw_outerpath = fdw_outerpath;
    pathnode->fdw_private = fdw_private;

    return pathnode;
}

/*
 * create_foreign_join_path
 *    Creates a path corresponding to a scan of a foreign join,
 *    returning the pathnode.
 *
 * This function is never called from core Postgres; rather, it's expected
 * to be called by the GetForeignJoinPaths function of a foreign data wrapper.
 * We make the FDW supply all fields of the path, since we do not have any way
 * to calculate them in core.  However, there is a usually-sane default for
 * the pathtarget (rel->reltarget), so we let a NULL for "target" select that.
 */
ForeignPath *
create_foreign_join_path(PlannerInfo *root, RelOptInfo *rel,
                         PathTarget *target,
                         double rows, Cost startup_cost, Cost total_cost,
                         List *pathkeys,
                         Relids required_outer,
                         Path *fdw_outerpath,
                         List *fdw_private)
{
    ForeignPath *pathnode = makeNode(ForeignPath);

    /*
     * We should use get_joinrel_parampathinfo to handle parameterized paths,
     * but the API of this function doesn't support it, and existing
     * extensions aren't yet trying to build such paths anyway.  For the
     * moment just throw an error if someone tries it; eventually we should
     * revisit this.
     */
    if (!bms_is_empty(required_outer) || !bms_is_empty(rel->lateral_relids))
        elog(ERROR, "parameterized foreign joins are not supported yet");

    pathnode->path.pathtype = T_ForeignScan;
    pathnode->path.parent = rel;
    pathnode->path.pathtarget = target ? target : rel->reltarget;
    pathnode->path.param_info = NULL;   /* XXX see above */
    pathnode->path.parallel_aware = false;
    pathnode->path.parallel_safe = rel->consider_parallel;
    pathnode->path.parallel_workers = 0;
    pathnode->path.rows = rows;
    pathnode->path.startup_cost = startup_cost;
    pathnode->path.total_cost = total_cost;
    pathnode->path.pathkeys = pathkeys;

    pathnode->fdw_outerpath = fdw_outerpath;
    pathnode->fdw_private = fdw_private;

    return pathnode;
}

/*
 * create_foreign_upper_path
 *    Creates a path corresponding to an upper relation that's computed
 *    directly by an FDW, returning the pathnode.
 *
 * This function is never called from core Postgres; rather, it's expected to
 * be called by the GetForeignUpperPaths function of a foreign data wrapper.
 * We make the FDW supply all fields of the path, since we do not have any way
 * to calculate them in core.  However, there is a usually-sane default for
 * the pathtarget (rel->reltarget), so we let a NULL for "target" select that.
 */
ForeignPath *
create_foreign_upper_path(PlannerInfo *root, RelOptInfo *rel,
                          PathTarget *target,
                          double rows, Cost startup_cost, Cost total_cost,
                          List *pathkeys,
                          Path *fdw_outerpath,
                          List *fdw_private)
{
    ForeignPath *pathnode = makeNode(ForeignPath);

    /*
     * Upper relations should never have any lateral references, since joining
     * is complete.
     */
    Assert(bms_is_empty(rel->lateral_relids));

    pathnode->path.pathtype = T_ForeignScan;
    pathnode->path.parent = rel;
    pathnode->path.pathtarget = target ? target : rel->reltarget;
    pathnode->path.param_info = NULL;
    pathnode->path.parallel_aware = false;
    pathnode->path.parallel_safe = rel->consider_parallel;
    pathnode->path.parallel_workers = 0;
    pathnode->path.rows = rows;
    pathnode->path.startup_cost = startup_cost;
    pathnode->path.total_cost = total_cost;
    pathnode->path.pathkeys = pathkeys;

    pathnode->fdw_outerpath = fdw_outerpath;
    pathnode->fdw_private = fdw_private;

    return pathnode;
}

/*
 * calc_nestloop_required_outer
 *    Compute the required_outer set for a nestloop join path
 *
 * Note: result must not share storage with either input
 */
Relids
calc_nestloop_required_outer(Relids outerrelids,
                             Relids outer_paramrels,
                             Relids innerrelids,
                             Relids inner_paramrels)
{
    Relids      required_outer;

    /* inner_path can require rels from outer path, but not vice versa */
    Assert(!bms_overlap(outer_paramrels, innerrelids));
    /* easy case if inner path is not parameterized */
    if (!inner_paramrels)
        return bms_copy(outer_paramrels);
    /* else, form the union ... */
    required_outer = bms_union(outer_paramrels, inner_paramrels);
    /* ... and remove any mention of now-satisfied outer rels */
    required_outer = bms_del_members(required_outer,
                                     outerrelids);
    /* maintain invariant that required_outer is exactly NULL if empty */
    if (bms_is_empty(required_outer))
    {
        bms_free(required_outer);
        required_outer = NULL;
    }
    return required_outer;
}

/*
 * calc_non_nestloop_required_outer
 *    Compute the required_outer set for a merge or hash join path
 *
 * Note: result must not share storage with either input
 */
Relids
calc_non_nestloop_required_outer(Path *outer_path, Path *inner_path)
{
    Relids      outer_paramrels = PATH_REQ_OUTER(outer_path);
    Relids      inner_paramrels = PATH_REQ_OUTER(inner_path);
    Relids      required_outer;

    /* neither path can require rels from the other */
    Assert(!bms_overlap(outer_paramrels, inner_path->parent->relids));
    Assert(!bms_overlap(inner_paramrels, outer_path->parent->relids));
    /* form the union ... */
    required_outer = bms_union(outer_paramrels, inner_paramrels);
    /* we do not need an explicit test for empty; bms_union gets it right */
    return required_outer;
}

/*
 * create_nestloop_path
 *    Creates a pathnode corresponding to a nestloop join between two
 *    relations.
 *
 * 'joinrel' is the join relation.
 * 'jointype' is the type of join required
 * 'workspace' is the result from initial_cost_nestloop
 * 'extra' contains various information about the join
 * 'outer_path' is the outer path
 * 'inner_path' is the inner path
 * 'restrict_clauses' are the RestrictInfo nodes to apply at the join
 * 'pathkeys' are the path keys of the new join path
 * 'required_outer' is the set of required outer rels
 *
 * Returns the resulting path node.
 */
NestPath *
create_nestloop_path(PlannerInfo *root,
                     RelOptInfo *joinrel,
                     JoinType jointype,
                     JoinCostWorkspace *workspace,
                     JoinPathExtraData *extra,
                     Path *outer_path,
                     Path *inner_path,
                     List *restrict_clauses,
                     List *pathkeys,
                     Relids required_outer)
{
    NestPath   *pathnode = makeNode(NestPath);
    Relids      inner_req_outer = PATH_REQ_OUTER(inner_path);

    /*
     * If the inner path is parameterized by the outer, we must drop any
     * restrict_clauses that are due to be moved into the inner path.  We have
     * to do this now, rather than postpone the work till createplan time,
     * because the restrict_clauses list can affect the size and cost
     * estimates for this path.
     */
    if (bms_overlap(inner_req_outer, outer_path->parent->relids))
    {
        Relids      inner_and_outer = bms_union(inner_path->parent->relids,
                                                inner_req_outer);
        List       *jclauses = NIL;
        ListCell   *lc;

        foreach(lc, restrict_clauses)
        {
            RestrictInfo *rinfo = (RestrictInfo *) lfirst(lc);

            if (!join_clause_is_movable_into(rinfo,
                                             inner_path->parent->relids,
                                             inner_and_outer))
                jclauses = lappend(jclauses, rinfo);
        }
        restrict_clauses = jclauses;
    }

    pathnode->path.pathtype = T_NestLoop;
    pathnode->path.parent = joinrel;
    pathnode->path.pathtarget = joinrel->reltarget;
    pathnode->path.param_info =
        get_joinrel_parampathinfo(root,
                                  joinrel,
                                  outer_path,
                                  inner_path,
                                  extra->sjinfo,
                                  required_outer,
                                  &restrict_clauses);
    pathnode->path.parallel_aware = false;
    pathnode->path.parallel_safe = joinrel->consider_parallel &&
        outer_path->parallel_safe && inner_path->parallel_safe;
    /* This is a foolish way to estimate parallel_workers, but for now... */
    pathnode->path.parallel_workers = outer_path->parallel_workers;
    pathnode->path.pathkeys = pathkeys;
    pathnode->jointype = jointype;
    pathnode->inner_unique = extra->inner_unique;
    pathnode->outerjoinpath = outer_path;
    pathnode->innerjoinpath = inner_path;
    pathnode->joinrestrictinfo = restrict_clauses;

    final_cost_nestloop(root, pathnode, workspace, extra);

    return pathnode;
}

/*
 * create_mergejoin_path
 *    Creates a pathnode corresponding to a mergejoin join between
 *    two relations
 *
 * 'joinrel' is the join relation
 * 'jointype' is the type of join required
 * 'workspace' is the result from initial_cost_mergejoin
 * 'extra' contains various information about the join
 * 'outer_path' is the outer path
 * 'inner_path' is the inner path
 * 'restrict_clauses' are the RestrictInfo nodes to apply at the join
 * 'pathkeys' are the path keys of the new join path
 * 'required_outer' is the set of required outer rels
 * 'mergeclauses' are the RestrictInfo nodes to use as merge clauses
 *      (this should be a subset of the restrict_clauses list)
 * 'outersortkeys' are the sort varkeys for the outer relation
 * 'innersortkeys' are the sort varkeys for the inner relation
 */
MergePath *
create_mergejoin_path(PlannerInfo *root,
                      RelOptInfo *joinrel,
                      JoinType jointype,
                      JoinCostWorkspace *workspace,
                      JoinPathExtraData *extra,
                      Path *outer_path,
                      Path *inner_path,
                      List *restrict_clauses,
                      List *pathkeys,
                      Relids required_outer,
                      List *mergeclauses,
                      List *outersortkeys,
                      List *innersortkeys)
{
    MergePath  *pathnode = makeNode(MergePath);

    pathnode->jpath.path.pathtype = T_MergeJoin;
    pathnode->jpath.path.parent = joinrel;
    pathnode->jpath.path.pathtarget = joinrel->reltarget;
    pathnode->jpath.path.param_info =
        get_joinrel_parampathinfo(root,
                                  joinrel,
                                  outer_path,
                                  inner_path,
                                  extra->sjinfo,
                                  required_outer,
                                  &restrict_clauses);
    pathnode->jpath.path.parallel_aware = false;
    pathnode->jpath.path.parallel_safe = joinrel->consider_parallel &&
        outer_path->parallel_safe && inner_path->parallel_safe;
    /* This is a foolish way to estimate parallel_workers, but for now... */
    pathnode->jpath.path.parallel_workers = outer_path->parallel_workers;
    pathnode->jpath.path.pathkeys = pathkeys;
    pathnode->jpath.jointype = jointype;
    pathnode->jpath.inner_unique = extra->inner_unique;
    pathnode->jpath.outerjoinpath = outer_path;
    pathnode->jpath.innerjoinpath = inner_path;
    pathnode->jpath.joinrestrictinfo = restrict_clauses;
    pathnode->path_mergeclauses = mergeclauses;
    pathnode->outersortkeys = outersortkeys;
    pathnode->innersortkeys = innersortkeys;
    /* pathnode->skip_mark_restore will be set by final_cost_mergejoin */
    /* pathnode->materialize_inner will be set by final_cost_mergejoin */

    final_cost_mergejoin(root, pathnode, workspace, extra);

    return pathnode;
}

/*
 * create_hashjoin_path
 *    Creates a pathnode corresponding to a hash join between two relations.
 *
 * 'joinrel' is the join relation
 * 'jointype' is the type of join required
 * 'workspace' is the result from initial_cost_hashjoin
 * 'extra' contains various information about the join
 * 'outer_path' is the cheapest outer path
 * 'inner_path' is the cheapest inner path
 * 'parallel_hash' to select Parallel Hash of inner path (shared hash table)
 * 'restrict_clauses' are the RestrictInfo nodes to apply at the join
 * 'required_outer' is the set of required outer rels
 * 'hashclauses' are the RestrictInfo nodes to use as hash clauses
 *      (this should be a subset of the restrict_clauses list)
 */
HashPath *
create_hashjoin_path(PlannerInfo *root,
                     RelOptInfo *joinrel,
                     JoinType jointype,
                     JoinCostWorkspace *workspace,
                     JoinPathExtraData *extra,
                     Path *outer_path,
                     Path *inner_path,
                     bool parallel_hash,
                     List *restrict_clauses,
                     Relids required_outer,
                     List *hashclauses)
{
    HashPath   *pathnode = makeNode(HashPath);

    pathnode->jpath.path.pathtype = T_HashJoin;
    pathnode->jpath.path.parent = joinrel;
    pathnode->jpath.path.pathtarget = joinrel->reltarget;
    pathnode->jpath.path.param_info =
        get_joinrel_parampathinfo(root,
                                  joinrel,
                                  outer_path,
                                  inner_path,
                                  extra->sjinfo,
                                  required_outer,
                                  &restrict_clauses);
    pathnode->jpath.path.parallel_aware =
        joinrel->consider_parallel && parallel_hash;
    pathnode->jpath.path.parallel_safe = joinrel->consider_parallel &&
        outer_path->parallel_safe && inner_path->parallel_safe;
    /* This is a foolish way to estimate parallel_workers, but for now... */
    pathnode->jpath.path.parallel_workers = outer_path->parallel_workers;

    /*
     * A hashjoin never has pathkeys, since its output ordering is
     * unpredictable due to possible batching.  XXX If the inner relation is
     * small enough, we could instruct the executor that it must not batch,
     * and then we could assume that the output inherits the outer relation's
     * ordering, which might save a sort step.  However there is considerable
     * downside if our estimate of the inner relation size is badly off. For
     * the moment we don't risk it.  (Note also that if we wanted to take this
     * seriously, joinpath.c would have to consider many more paths for the
     * outer rel than it does now.)
     */
    pathnode->jpath.path.pathkeys = NIL;
    pathnode->jpath.jointype = jointype;
    pathnode->jpath.inner_unique = extra->inner_unique;
    pathnode->jpath.outerjoinpath = outer_path;
    pathnode->jpath.innerjoinpath = inner_path;
    pathnode->jpath.joinrestrictinfo = restrict_clauses;
    pathnode->path_hashclauses = hashclauses;
    /* final_cost_hashjoin will fill in pathnode->num_batches */

    final_cost_hashjoin(root, pathnode, workspace, extra);

    return pathnode;
}

/*
 * create_projection_path
 *    Creates a pathnode that represents performing a projection.
 *
 * 'rel' is the parent relation associated with the result
 * 'subpath' is the path representing the source of data
 * 'target' is the PathTarget to be computed
 */
ProjectionPath *
create_projection_path(PlannerInfo *root,
                       RelOptInfo *rel,
                       Path *subpath,
                       PathTarget *target)
{
    ProjectionPath *pathnode = makeNode(ProjectionPath);
    PathTarget *oldtarget = subpath->pathtarget;

    pathnode->path.pathtype = T_Result;
    pathnode->path.parent = rel;
    pathnode->path.pathtarget = target;
    /* For now, assume we are above any joins, so no parameterization */
    pathnode->path.param_info = NULL;
    pathnode->path.parallel_aware = false;
    pathnode->path.parallel_safe = rel->consider_parallel &&
        subpath->parallel_safe &&
        is_parallel_safe(root, (Node *) target->exprs);
    pathnode->path.parallel_workers = subpath->parallel_workers;
    /* Projection does not change the sort order */
    pathnode->path.pathkeys = subpath->pathkeys;

    pathnode->subpath = subpath;

    /*
     * We might not need a separate Result node.  If the input plan node type
     * can project, we can just tell it to project something else.  Or, if it
     * can't project but the desired target has the same expression list as
     * what the input will produce anyway, we can still give it the desired
     * tlist (possibly changing its ressortgroupref labels, but nothing else).
     * Note: in the latter case, create_projection_plan has to recheck our
     * conclusion; see comments therein.
     */
    if (is_projection_capable_path(subpath) ||
        equal(oldtarget->exprs, target->exprs))
    {
        /* No separate Result node needed */
        pathnode->dummypp = true;

        /*
         * Set cost of plan as subpath's cost, adjusted for tlist replacement.
         */
        pathnode->path.rows = subpath->rows;
        pathnode->path.startup_cost = subpath->startup_cost +
            (target->cost.startup - oldtarget->cost.startup);
        pathnode->path.total_cost = subpath->total_cost +
            (target->cost.startup - oldtarget->cost.startup) +
            (target->cost.per_tuple - oldtarget->cost.per_tuple) * subpath->rows;
    }
    else
    {
        /* We really do need the Result node */
        pathnode->dummypp = false;

        /*
         * The Result node's cost is cpu_tuple_cost per row, plus the cost of
         * evaluating the tlist.  There is no qual to worry about.
         */
        pathnode->path.rows = subpath->rows;
        pathnode->path.startup_cost = subpath->startup_cost +
            target->cost.startup;
        pathnode->path.total_cost = subpath->total_cost +
            target->cost.startup +
            (cpu_tuple_cost + target->cost.per_tuple) * subpath->rows;
    }

    return pathnode;
}

/*
 * apply_projection_to_path
 *    Add a projection step, or just apply the target directly to given path.
 *
 * This has the same net effect as create_projection_path(), except that if
 * a separate Result plan node isn't needed, we just replace the given path's
 * pathtarget with the desired one.  This must be used only when the caller
 * knows that the given path isn't referenced elsewhere and so can be modified
 * in-place.
 *
 * If the input path is a GatherPath or GatherMergePath, we try to push the
 * new target down to its input as well; this is a yet more invasive
 * modification of the input path, which create_projection_path() can't do.
 *
 * Note that we mustn't change the source path's parent link; so when it is
 * add_path'd to "rel" things will be a bit inconsistent.  So far that has
 * not caused any trouble.
 *
 * 'rel' is the parent relation associated with the result
 * 'path' is the path representing the source of data
 * 'target' is the PathTarget to be computed
 */
Path *
apply_projection_to_path(PlannerInfo *root,
                         RelOptInfo *rel,
                         Path *path,
                         PathTarget *target)
{
    QualCost    oldcost;

    /*
     * If given path can't project, we might need a Result node, so make a
     * separate ProjectionPath.
     */
    if (!is_projection_capable_path(path))
        return (Path *) create_projection_path(root, rel, path, target);

    /*
     * We can just jam the desired tlist into the existing path, being sure to
     * update its cost estimates appropriately.
     */
    oldcost = path->pathtarget->cost;
    path->pathtarget = target;

    path->startup_cost += target->cost.startup - oldcost.startup;
    path->total_cost += target->cost.startup - oldcost.startup +
        (target->cost.per_tuple - oldcost.per_tuple) * path->rows;

    /*
     * If the path happens to be a Gather or GatherMerge path, we'd like to
     * arrange for the subpath to return the required target list so that
     * workers can help project.  But if there is something that is not
     * parallel-safe in the target expressions, then we can't.
     */
    if ((IsA(path, GatherPath) || IsA(path, GatherMergePath)) &&
        is_parallel_safe(root, (Node *) target->exprs))
    {
        /*
         * We always use create_projection_path here, even if the subpath is
         * projection-capable, so as to avoid modifying the subpath in place.
         * It seems unlikely at present that there could be any other
         * references to the subpath, but better safe than sorry.
         *
         * Note that we don't change the parallel path's cost estimates; it
         * might be appropriate to do so, to reflect the fact that the bulk of
         * the target evaluation will happen in workers.
         */
        if (IsA(path, GatherPath))
        {
            GatherPath *gpath = (GatherPath *) path;

            gpath->subpath = (Path *)
                create_projection_path(root,
                                       gpath->subpath->parent,
                                       gpath->subpath,
                                       target);
        }
        else
        {
            GatherMergePath *gmpath = (GatherMergePath *) path;

            gmpath->subpath = (Path *)
                create_projection_path(root,
                                       gmpath->subpath->parent,
                                       gmpath->subpath,
                                       target);
        }
    }
    else if (path->parallel_safe &&
             !is_parallel_safe(root, (Node *) target->exprs))
    {
        /*
         * We're inserting a parallel-restricted target list into a path
         * currently marked parallel-safe, so we have to mark it as no longer
         * safe.
         */
        path->parallel_safe = false;
    }

    return path;
}

/*
 * create_set_projection_path
 *    Creates a pathnode that represents performing a projection that
 *    includes set-returning functions.
 *
 * 'rel' is the parent relation associated with the result
 * 'subpath' is the path representing the source of data
 * 'target' is the PathTarget to be computed
 */
ProjectSetPath *
create_set_projection_path(PlannerInfo *root,
                           RelOptInfo *rel,
                           Path *subpath,
                           PathTarget *target)
{
    ProjectSetPath *pathnode = makeNode(ProjectSetPath);
    double      tlist_rows;
    ListCell   *lc;

    pathnode->path.pathtype = T_ProjectSet;
    pathnode->path.parent = rel;
    pathnode->path.pathtarget = target;
    /* For now, assume we are above any joins, so no parameterization */
    pathnode->path.param_info = NULL;
    pathnode->path.parallel_aware = false;
    pathnode->path.parallel_safe = rel->consider_parallel &&
        subpath->parallel_safe &&
        is_parallel_safe(root, (Node *) target->exprs);
    pathnode->path.parallel_workers = subpath->parallel_workers;
    /* Projection does not change the sort order XXX? */
    pathnode->path.pathkeys = subpath->pathkeys;

    pathnode->subpath = subpath;

    /*
     * Estimate number of rows produced by SRFs for each row of input; if
     * there's more than one in this node, use the maximum.
     */
    tlist_rows = 1;
    foreach(lc, target->exprs)
    {
        Node       *node = (Node *) lfirst(lc);
        double      itemrows;

        itemrows = expression_returns_set_rows(root, node);
        if (tlist_rows < itemrows)
            tlist_rows = itemrows;
    }

    /*
     * In addition to the cost of evaluating the tlist, charge cpu_tuple_cost
     * per input row, and half of cpu_tuple_cost for each added output row.
     * This is slightly bizarre maybe, but it's what 9.6 did; we may revisit
     * this estimate later.
     */
    pathnode->path.rows = subpath->rows * tlist_rows;
    pathnode->path.startup_cost = subpath->startup_cost +
        target->cost.startup;
    pathnode->path.total_cost = subpath->total_cost +
        target->cost.startup +
        (cpu_tuple_cost + target->cost.per_tuple) * subpath->rows +
        (pathnode->path.rows - subpath->rows) * cpu_tuple_cost / 2;

    return pathnode;
}

/*
 * create_incremental_sort_path
 *    Creates a pathnode that represents performing an incremental sort.
 *
 * 'rel' is the parent relation associated with the result
 * 'subpath' is the path representing the source of data
 * 'pathkeys' represents the desired sort order
 * 'presorted_keys' is the number of keys by which the input path is
 *      already sorted
 * 'limit_tuples' is the estimated bound on the number of output tuples,
 *      or -1 if no LIMIT or couldn't estimate
 */
SortPath *
create_incremental_sort_path(PlannerInfo *root,
                             RelOptInfo *rel,
                             Path *subpath,
                             List *pathkeys,
                             int presorted_keys,
                             double limit_tuples)
{
    IncrementalSortPath *sort = makeNode(IncrementalSortPath);
    SortPath   *pathnode = &sort->spath;

    pathnode->path.pathtype = T_IncrementalSort;
    pathnode->path.parent = rel;
    /* Sort doesn't project, so use source path's pathtarget */
    pathnode->path.pathtarget = subpath->pathtarget;
    /* For now, assume we are above any joins, so no parameterization */
    pathnode->path.param_info = NULL;
    pathnode->path.parallel_aware = false;
    pathnode->path.parallel_safe = rel->consider_parallel &&
        subpath->parallel_safe;
    pathnode->path.parallel_workers = subpath->parallel_workers;
    pathnode->path.pathkeys = pathkeys;

    pathnode->subpath = subpath;

    cost_incremental_sort(&pathnode->path,
                          root, pathkeys, presorted_keys,
                          subpath->startup_cost,
                          subpath->total_cost,
                          subpath->rows,
                          subpath->pathtarget->width,
                          0.0,  /* XXX comparison_cost shouldn't be 0? */
                          work_mem, limit_tuples);

    sort->nPresortedCols = presorted_keys;

    return pathnode;
}

/*
 * create_sort_path
 *    Creates a pathnode that represents performing an explicit sort.
 *
 * 'rel' is the parent relation associated with the result
 * 'subpath' is the path representing the source of data
 * 'pathkeys' represents the desired sort order
 * 'limit_tuples' is the estimated bound on the number of output tuples,
 *      or -1 if no LIMIT or couldn't estimate
 */
SortPath *
create_sort_path(PlannerInfo *root,
                 RelOptInfo *rel,
                 Path *subpath,
                 List *pathkeys,
                 double limit_tuples)
{
    SortPath   *pathnode = makeNode(SortPath);

    pathnode->path.pathtype = T_Sort;
    pathnode->path.parent = rel;
    /* Sort doesn't project, so use source path's pathtarget */
    pathnode->path.pathtarget = subpath->pathtarget;
    /* For now, assume we are above any joins, so no parameterization */
    pathnode->path.param_info = NULL;
    pathnode->path.parallel_aware = false;
    pathnode->path.parallel_safe = rel->consider_parallel &&
        subpath->parallel_safe;
    pathnode->path.parallel_workers = subpath->parallel_workers;
    pathnode->path.pathkeys = pathkeys;

    pathnode->subpath = subpath;

    cost_sort(&pathnode->path, root, pathkeys,
              subpath->total_cost,
              subpath->rows,
              subpath->pathtarget->width,
              0.0,              /* XXX comparison_cost shouldn't be 0? */
              work_mem, limit_tuples);

    return pathnode;
}

/*
 * create_group_path
 *    Creates a pathnode that represents performing grouping of presorted input
 *
 * 'rel' is the parent relation associated with the result
 * 'subpath' is the path representing the source of data
 * 'target' is the PathTarget to be computed
 * 'groupClause' is a list of SortGroupClause's representing the grouping
 * 'qual' is the HAVING quals if any
 * 'numGroups' is the estimated number of groups
 */
GroupPath *
create_group_path(PlannerInfo *root,
                  RelOptInfo *rel,
                  Path *subpath,
                  List *groupClause,
                  List *qual,
                  double numGroups)
{
    GroupPath  *pathnode = makeNode(GroupPath);
    PathTarget *target = rel->reltarget;

    pathnode->path.pathtype = T_Group;
    pathnode->path.parent = rel;
    pathnode->path.pathtarget = target;
    /* For now, assume we are above any joins, so no parameterization */
    pathnode->path.param_info = NULL;
    pathnode->path.parallel_aware = false;
    pathnode->path.parallel_safe = rel->consider_parallel &&
        subpath->parallel_safe;
    pathnode->path.parallel_workers = subpath->parallel_workers;
    /* Group doesn't change sort ordering */
    pathnode->path.pathkeys = subpath->pathkeys;

    pathnode->subpath = subpath;

    pathnode->groupClause = groupClause;
    pathnode->qual = qual;

    cost_group(&pathnode->path, root,
               list_length(groupClause),
               numGroups,
               qual,
               subpath->startup_cost, subpath->total_cost,
               subpath->rows);

    /* add tlist eval cost for each output row */
    pathnode->path.startup_cost += target->cost.startup;
    pathnode->path.total_cost += target->cost.startup +
        target->cost.per_tuple * pathnode->path.rows;

    return pathnode;
}

/*
 * create_upper_unique_path
 *    Creates a pathnode that represents performing an explicit Unique step
 *    on presorted input.
 *
 * This produces a Unique plan node, but the use-case is so different from
 * create_unique_path that it doesn't seem worth trying to merge the two.
 *
 * 'rel' is the parent relation associated with the result
 * 'subpath' is the path representing the source of data
 * 'numCols' is the number of grouping columns
 * 'numGroups' is the estimated number of groups
 *
 * The input path must be sorted on the grouping columns, plus possibly
 * additional columns; so the first numCols pathkeys are the grouping columns
 */
UpperUniquePath *
create_upper_unique_path(PlannerInfo *root,
                         RelOptInfo *rel,
                         Path *subpath,
                         int numCols,
                         double numGroups)
{
    UpperUniquePath *pathnode = makeNode(UpperUniquePath);

    pathnode->path.pathtype = T_Unique;
    pathnode->path.parent = rel;
    /* Unique doesn't project, so use source path's pathtarget */
    pathnode->path.pathtarget = subpath->pathtarget;
    /* For now, assume we are above any joins, so no parameterization */
    pathnode->path.param_info = NULL;
    pathnode->path.parallel_aware = false;
    pathnode->path.parallel_safe = rel->consider_parallel &&
        subpath->parallel_safe;
    pathnode->path.parallel_workers = subpath->parallel_workers;
    /* Unique doesn't change the input ordering */
    pathnode->path.pathkeys = subpath->pathkeys;

    pathnode->subpath = subpath;
    pathnode->numkeys = numCols;

    /*
     * Charge one cpu_operator_cost per comparison per input tuple. We assume
     * all columns get compared at most of the tuples.  (XXX probably this is
     * an overestimate.)
     */
    pathnode->path.startup_cost = subpath->startup_cost;
    pathnode->path.total_cost = subpath->total_cost +
        cpu_operator_cost * subpath->rows * numCols;
    pathnode->path.rows = numGroups;

    return pathnode;
}

/*
 * create_agg_path
 *    Creates a pathnode that represents performing aggregation/grouping
 *
 * 'rel' is the parent relation associated with the result
 * 'subpath' is the path representing the source of data
 * 'target' is the PathTarget to be computed
 * 'aggstrategy' is the Agg node's basic implementation strategy
 * 'aggsplit' is the Agg node's aggregate-splitting mode
 * 'groupClause' is a list of SortGroupClause's representing the grouping
 * 'qual' is the HAVING quals if any
 * 'aggcosts' contains cost info about the aggregate functions to be computed
 * 'numGroups' is the estimated number of groups (1 if not grouping)
 */
AggPath *
create_agg_path(PlannerInfo *root,
                RelOptInfo *rel,
                Path *subpath,
                PathTarget *target,
                AggStrategy aggstrategy,
                AggSplit aggsplit,
                List *groupClause,
                List *qual,
                const AggClauseCosts *aggcosts,
                double numGroups)
{
    AggPath    *pathnode = makeNode(AggPath);

    pathnode->path.pathtype = T_Agg;
    pathnode->path.parent = rel;
    pathnode->path.pathtarget = target;
    /* For now, assume we are above any joins, so no parameterization */
    pathnode->path.param_info = NULL;
    pathnode->path.parallel_aware = false;
    pathnode->path.parallel_safe = rel->consider_parallel &&
        subpath->parallel_safe;
    pathnode->path.parallel_workers = subpath->parallel_workers;
    if (aggstrategy == AGG_SORTED)
        pathnode->path.pathkeys = subpath->pathkeys;    /* preserves order */
    else
        pathnode->path.pathkeys = NIL;  /* output is unordered */
    pathnode->subpath = subpath;

    pathnode->aggstrategy = aggstrategy;
    pathnode->aggsplit = aggsplit;
    pathnode->numGroups = numGroups;
    pathnode->transitionSpace = aggcosts ? aggcosts->transitionSpace : 0;
    pathnode->groupClause = groupClause;
    pathnode->qual = qual;

    cost_agg(&pathnode->path, root,
             aggstrategy, aggcosts,
             list_length(groupClause), numGroups,
             qual,
             subpath->startup_cost, subpath->total_cost,
             subpath->rows, subpath->pathtarget->width);

    /* add tlist eval cost for each output row */
    pathnode->path.startup_cost += target->cost.startup;
    pathnode->path.total_cost += target->cost.startup +
        target->cost.per_tuple * pathnode->path.rows;

    return pathnode;
}

/*
 * create_groupingsets_path
 *    Creates a pathnode that represents performing GROUPING SETS aggregation
 *
 * GroupingSetsPath represents sorted grouping with one or more grouping sets.
 * The input path's result must be sorted to match the last entry in
 * rollup_groupclauses.
 *
 * 'rel' is the parent relation associated with the result
 * 'subpath' is the path representing the source of data
 * 'target' is the PathTarget to be computed
 * 'having_qual' is the HAVING quals if any
 * 'rollups' is a list of RollupData nodes
 * 'agg_costs' contains cost info about the aggregate functions to be computed
 * 'numGroups' is the estimated total number of groups
 */
GroupingSetsPath *
create_groupingsets_path(PlannerInfo *root,
                         RelOptInfo *rel,
                         Path *subpath,
                         List *having_qual,
                         AggStrategy aggstrategy,
                         List *rollups,
                         const AggClauseCosts *agg_costs,
                         double numGroups)
{
    GroupingSetsPath *pathnode = makeNode(GroupingSetsPath);
    PathTarget *target = rel->reltarget;
    ListCell   *lc;
    bool        is_first = true;
    bool        is_first_sort = true;

    /* The topmost generated Plan node will be an Agg */
    pathnode->path.pathtype = T_Agg;
    pathnode->path.parent = rel;
    pathnode->path.pathtarget = target;
    pathnode->path.param_info = subpath->param_info;
    pathnode->path.parallel_aware = false;
    pathnode->path.parallel_safe = rel->consider_parallel &&
        subpath->parallel_safe;
    pathnode->path.parallel_workers = subpath->parallel_workers;
    pathnode->subpath = subpath;

    /*
     * Simplify callers by downgrading AGG_SORTED to AGG_PLAIN, and AGG_MIXED
     * to AGG_HASHED, here if possible.
     */
    if (aggstrategy == AGG_SORTED &&
        list_length(rollups) == 1 &&
        ((RollupData *) linitial(rollups))->groupClause == NIL)
        aggstrategy = AGG_PLAIN;

    if (aggstrategy == AGG_MIXED &&
        list_length(rollups) == 1)
        aggstrategy = AGG_HASHED;

    /*
     * Output will be in sorted order by group_pathkeys if, and only if, there
     * is a single rollup operation on a non-empty list of grouping
     * expressions.
     */
    if (aggstrategy == AGG_SORTED && list_length(rollups) == 1)
        pathnode->path.pathkeys = root->group_pathkeys;
    else
        pathnode->path.pathkeys = NIL;

    pathnode->aggstrategy = aggstrategy;
    pathnode->rollups = rollups;
    pathnode->qual = having_qual;
    pathnode->transitionSpace = agg_costs ? agg_costs->transitionSpace : 0;

    Assert(rollups != NIL);
    Assert(aggstrategy != AGG_PLAIN || list_length(rollups) == 1);
    Assert(aggstrategy != AGG_MIXED || list_length(rollups) > 1);

    foreach(lc, rollups)
    {
        RollupData *rollup = lfirst(lc);
        List       *gsets = rollup->gsets;
        int         numGroupCols = list_length(linitial(gsets));

        /*
         * In AGG_SORTED or AGG_PLAIN mode, the first rollup takes the
         * (already-sorted) input, and following ones do their own sort.
         *
         * In AGG_HASHED mode, there is one rollup for each grouping set.
         *
         * In AGG_MIXED mode, the first rollups are hashed, the first
         * non-hashed one takes the (already-sorted) input, and following ones
         * do their own sort.
         */
        if (is_first)
        {
            cost_agg(&pathnode->path, root,
                     aggstrategy,
                     agg_costs,
                     numGroupCols,
                     rollup->numGroups,
                     having_qual,
                     subpath->startup_cost,
                     subpath->total_cost,
                     subpath->rows,
                     subpath->pathtarget->width);
            is_first = false;
            if (!rollup->is_hashed)
                is_first_sort = false;
        }
        else
        {
            Path        sort_path;  /* dummy for result of cost_sort */
            Path        agg_path;   /* dummy for result of cost_agg */

            if (rollup->is_hashed || is_first_sort)
            {
                /*
                 * Account for cost of aggregation, but don't charge input
                 * cost again
                 */
                cost_agg(&agg_path, root,
                         rollup->is_hashed ? AGG_HASHED : AGG_SORTED,
                         agg_costs,
                         numGroupCols,
                         rollup->numGroups,
                         having_qual,
                         0.0, 0.0,
                         subpath->rows,
                         subpath->pathtarget->width);
                if (!rollup->is_hashed)
                    is_first_sort = false;
            }
            else
            {
                /* Account for cost of sort, but don't charge input cost again */
                cost_sort(&sort_path, root, NIL,
                          0.0,
                          subpath->rows,
                          subpath->pathtarget->width,
                          0.0,
                          work_mem,
                          -1.0);

                /* Account for cost of aggregation */

                cost_agg(&agg_path, root,
                         AGG_SORTED,
                         agg_costs,
                         numGroupCols,
                         rollup->numGroups,
                         having_qual,
                         sort_path.startup_cost,
                         sort_path.total_cost,
                         sort_path.rows,
                         subpath->pathtarget->width);
            }

            pathnode->path.total_cost += agg_path.total_cost;
            pathnode->path.rows += agg_path.rows;
        }
    }

    /* add tlist eval cost for each output row */
    pathnode->path.startup_cost += target->cost.startup;
    pathnode->path.total_cost += target->cost.startup +
        target->cost.per_tuple * pathnode->path.rows;

    return pathnode;
}

/*
 * create_minmaxagg_path
 *    Creates a pathnode that represents computation of MIN/MAX aggregates
 *
 * 'rel' is the parent relation associated with the result
 * 'target' is the PathTarget to be computed
 * 'mmaggregates' is a list of MinMaxAggInfo structs
 * 'quals' is the HAVING quals if any
 */
MinMaxAggPath *
create_minmaxagg_path(PlannerInfo *root,
                      RelOptInfo *rel,
                      PathTarget *target,
                      List *mmaggregates,
                      List *quals)
{
    MinMaxAggPath *pathnode = makeNode(MinMaxAggPath);
    Cost        initplan_cost;
    ListCell   *lc;

    /* The topmost generated Plan node will be a Result */
    pathnode->path.pathtype = T_Result;
    pathnode->path.parent = rel;
    pathnode->path.pathtarget = target;
    /* For now, assume we are above any joins, so no parameterization */
    pathnode->path.param_info = NULL;
    pathnode->path.parallel_aware = false;
    /* A MinMaxAggPath implies use of subplans, so cannot be parallel-safe */
    pathnode->path.parallel_safe = false;
    pathnode->path.parallel_workers = 0;
    /* Result is one unordered row */
    pathnode->path.rows = 1;
    pathnode->path.pathkeys = NIL;

    pathnode->mmaggregates = mmaggregates;
    pathnode->quals = quals;

    /* Calculate cost of all the initplans ... */
    initplan_cost = 0;
    foreach(lc, mmaggregates)
    {
        MinMaxAggInfo *mminfo = (MinMaxAggInfo *) lfirst(lc);

        initplan_cost += mminfo->pathcost;
    }

    /* add tlist eval cost for each output row, plus cpu_tuple_cost */
    pathnode->path.startup_cost = initplan_cost + target->cost.startup;
    pathnode->path.total_cost = initplan_cost + target->cost.startup +
        target->cost.per_tuple + cpu_tuple_cost;

    /*
     * Add cost of qual, if any --- but we ignore its selectivity, since our
     * rowcount estimate should be 1 no matter what the qual is.
     */
    if (quals)
    {
        QualCost    qual_cost;

        cost_qual_eval(&qual_cost, quals, root);
        pathnode->path.startup_cost += qual_cost.startup;
        pathnode->path.total_cost += qual_cost.startup + qual_cost.per_tuple;
    }

    return pathnode;
}

/*
 * create_windowagg_path
 *    Creates a pathnode that represents computation of window functions
 *
 * 'rel' is the parent relation associated with the result
 * 'subpath' is the path representing the source of data
 * 'target' is the PathTarget to be computed
 * 'windowFuncs' is a list of WindowFunc structs
 * 'winclause' is a WindowClause that is common to all the WindowFuncs
 *
 * The input must be sorted according to the WindowClause's PARTITION keys
 * plus ORDER BY keys.
 */
WindowAggPath *
create_windowagg_path(PlannerInfo *root,
                      RelOptInfo *rel,
                      Path *subpath,
                      PathTarget *target,
                      List *windowFuncs,
                      WindowClause *winclause)
{
    WindowAggPath *pathnode = makeNode(WindowAggPath);

    pathnode->path.pathtype = T_WindowAgg;
    pathnode->path.parent = rel;
    pathnode->path.pathtarget = target;
    /* For now, assume we are above any joins, so no parameterization */
    pathnode->path.param_info = NULL;
    pathnode->path.parallel_aware = false;
    pathnode->path.parallel_safe = rel->consider_parallel &&
        subpath->parallel_safe;
    pathnode->path.parallel_workers = subpath->parallel_workers;
    /* WindowAgg preserves the input sort order */
    pathnode->path.pathkeys = subpath->pathkeys;

    pathnode->subpath = subpath;
    pathnode->winclause = winclause;

    /*
     * For costing purposes, assume that there are no redundant partitioning
     * or ordering columns; it's not worth the trouble to deal with that
     * corner case here.  So we just pass the unmodified list lengths to
     * cost_windowagg.
     */
    cost_windowagg(&pathnode->path, root,
                   windowFuncs,
                   list_length(winclause->partitionClause),
                   list_length(winclause->orderClause),
                   subpath->startup_cost,
                   subpath->total_cost,
                   subpath->rows);

    /* add tlist eval cost for each output row */
    pathnode->path.startup_cost += target->cost.startup;
    pathnode->path.total_cost += target->cost.startup +
        target->cost.per_tuple * pathnode->path.rows;

    return pathnode;
}

/*
 * create_setop_path
 *    Creates a pathnode that represents computation of INTERSECT or EXCEPT
 *
 * 'rel' is the parent relation associated with the result
 * 'subpath' is the path representing the source of data
 * 'cmd' is the specific semantics (INTERSECT or EXCEPT, with/without ALL)
 * 'strategy' is the implementation strategy (sorted or hashed)
 * 'distinctList' is a list of SortGroupClause's representing the grouping
 * 'flagColIdx' is the column number where the flag column will be, if any
 * 'firstFlag' is the flag value for the first input relation when hashing;
 *      or -1 when sorting
 * 'numGroups' is the estimated number of distinct groups
 * 'outputRows' is the estimated number of output rows
 */
SetOpPath *
create_setop_path(PlannerInfo *root,
                  RelOptInfo *rel,
                  Path *subpath,
                  SetOpCmd cmd,
                  SetOpStrategy strategy,
                  List *distinctList,
                  AttrNumber flagColIdx,
                  int firstFlag,
                  double numGroups,
                  double outputRows)
{
    SetOpPath  *pathnode = makeNode(SetOpPath);

    pathnode->path.pathtype = T_SetOp;
    pathnode->path.parent = rel;
    /* SetOp doesn't project, so use source path's pathtarget */
    pathnode->path.pathtarget = subpath->pathtarget;
    /* For now, assume we are above any joins, so no parameterization */
    pathnode->path.param_info = NULL;
    pathnode->path.parallel_aware = false;
    pathnode->path.parallel_safe = rel->consider_parallel &&
        subpath->parallel_safe;
    pathnode->path.parallel_workers = subpath->parallel_workers;
    /* SetOp preserves the input sort order if in sort mode */
    pathnode->path.pathkeys =
        (strategy == SETOP_SORTED) ? subpath->pathkeys : NIL;

    pathnode->subpath = subpath;
    pathnode->cmd = cmd;
    pathnode->strategy = strategy;
    pathnode->distinctList = distinctList;
    pathnode->flagColIdx = flagColIdx;
    pathnode->firstFlag = firstFlag;
    pathnode->numGroups = numGroups;

    /*
     * Charge one cpu_operator_cost per comparison per input tuple. We assume
     * all columns get compared at most of the tuples.
     */
    pathnode->path.startup_cost = subpath->startup_cost;
    pathnode->path.total_cost = subpath->total_cost +
        cpu_operator_cost * subpath->rows * list_length(distinctList);
    pathnode->path.rows = outputRows;

    return pathnode;
}

/*
 * create_recursiveunion_path
 *    Creates a pathnode that represents a recursive UNION node
 *
 * 'rel' is the parent relation associated with the result
 * 'leftpath' is the source of data for the non-recursive term
 * 'rightpath' is the source of data for the recursive term
 * 'target' is the PathTarget to be computed
 * 'distinctList' is a list of SortGroupClause's representing the grouping
 * 'wtParam' is the ID of Param representing work table
 * 'numGroups' is the estimated number of groups
 *
 * For recursive UNION ALL, distinctList is empty and numGroups is zero
 */
RecursiveUnionPath *
create_recursiveunion_path(PlannerInfo *root,
                           RelOptInfo *rel,
                           Path *leftpath,
                           Path *rightpath,
                           PathTarget *target,
                           List *distinctList,
                           int wtParam,
                           double numGroups)
{
    RecursiveUnionPath *pathnode = makeNode(RecursiveUnionPath);

    pathnode->path.pathtype = T_RecursiveUnion;
    pathnode->path.parent = rel;
    pathnode->path.pathtarget = target;
    /* For now, assume we are above any joins, so no parameterization */
    pathnode->path.param_info = NULL;
    pathnode->path.parallel_aware = false;
    pathnode->path.parallel_safe = rel->consider_parallel &&
        leftpath->parallel_safe && rightpath->parallel_safe;
    /* Foolish, but we'll do it like joins for now: */
    pathnode->path.parallel_workers = leftpath->parallel_workers;
    /* RecursiveUnion result is always unsorted */
    pathnode->path.pathkeys = NIL;

    pathnode->leftpath = leftpath;
    pathnode->rightpath = rightpath;
    pathnode->distinctList = distinctList;
    pathnode->wtParam = wtParam;
    pathnode->numGroups = numGroups;

    cost_recursive_union(&pathnode->path, leftpath, rightpath);

    return pathnode;
}

/*
 * create_lockrows_path
 *    Creates a pathnode that represents acquiring row locks
 *
 * 'rel' is the parent relation associated with the result
 * 'subpath' is the path representing the source of data
 * 'rowMarks' is a list of PlanRowMark's
 * 'epqParam' is the ID of Param for EvalPlanQual re-eval
 */
LockRowsPath *
create_lockrows_path(PlannerInfo *root, RelOptInfo *rel,
                     Path *subpath, List *rowMarks, int epqParam)
{
    LockRowsPath *pathnode = makeNode(LockRowsPath);

    pathnode->path.pathtype = T_LockRows;
    pathnode->path.parent = rel;
    /* LockRows doesn't project, so use source path's pathtarget */
    pathnode->path.pathtarget = subpath->pathtarget;
    /* For now, assume we are above any joins, so no parameterization */
    pathnode->path.param_info = NULL;
    pathnode->path.parallel_aware = false;
    pathnode->path.parallel_safe = false;
    pathnode->path.parallel_workers = 0;
    pathnode->path.rows = subpath->rows;

    /*
     * The result cannot be assumed sorted, since locking might cause the sort
     * key columns to be replaced with new values.
     */
    pathnode->path.pathkeys = NIL;

    pathnode->subpath = subpath;
    pathnode->rowMarks = rowMarks;
    pathnode->epqParam = epqParam;

    /*
     * We should charge something extra for the costs of row locking and
     * possible refetches, but it's hard to say how much.  For now, use
     * cpu_tuple_cost per row.
     */
    pathnode->path.startup_cost = subpath->startup_cost;
    pathnode->path.total_cost = subpath->total_cost +
        cpu_tuple_cost * subpath->rows;

    return pathnode;
}

/*
 * create_modifytable_path
 *    Creates a pathnode that represents performing INSERT/UPDATE/DELETE mods
 *
 * 'rel' is the parent relation associated with the result
 * 'operation' is the operation type
 * 'canSetTag' is true if we set the command tag/es_processed
 * 'nominalRelation' is the parent RT index for use of EXPLAIN
 * 'rootRelation' is the partitioned table root RT index, or 0 if none
 * 'partColsUpdated' is true if any partitioning columns are being updated,
 *      either from the target relation or a descendent partitioned table.
 * 'resultRelations' is an integer list of actual RT indexes of target rel(s)
 * 'subpaths' is a list of Path(s) producing source data (one per rel)
 * 'subroots' is a list of PlannerInfo structs (one per rel)
 * 'withCheckOptionLists' is a list of WCO lists (one per rel)
 * 'returningLists' is a list of RETURNING tlists (one per rel)
 * 'rowMarks' is a list of PlanRowMarks (non-locking only)
 * 'onconflict' is the ON CONFLICT clause, or NULL
 * 'epqParam' is the ID of Param for EvalPlanQual re-eval
 */
ModifyTablePath *
create_modifytable_path(PlannerInfo *root, RelOptInfo *rel,
                        CmdType operation, bool canSetTag,
                        Index nominalRelation, Index rootRelation,
                        bool partColsUpdated,
                        List *resultRelations, List *subpaths,
                        List *subroots,
                        List *withCheckOptionLists, List *returningLists,
                        List *rowMarks, OnConflictExpr *onconflict,
                        int epqParam)
{
    ModifyTablePath *pathnode = makeNode(ModifyTablePath);
    double      total_size;
    ListCell   *lc;

    Assert(list_length(resultRelations) == list_length(subpaths));
    Assert(list_length(resultRelations) == list_length(subroots));
    Assert(withCheckOptionLists == NIL ||
           list_length(resultRelations) == list_length(withCheckOptionLists));
    Assert(returningLists == NIL ||
           list_length(resultRelations) == list_length(returningLists));

    pathnode->path.pathtype = T_ModifyTable;
    pathnode->path.parent = rel;
    /* pathtarget is not interesting, just make it minimally valid */
    pathnode->path.pathtarget = rel->reltarget;
    /* For now, assume we are above any joins, so no parameterization */
    pathnode->path.param_info = NULL;
    pathnode->path.parallel_aware = false;
    pathnode->path.parallel_safe = false;
    pathnode->path.parallel_workers = 0;
    pathnode->path.pathkeys = NIL;

    /*
     * Compute cost & rowcount as sum of subpath costs & rowcounts.
     *
     * Currently, we don't charge anything extra for the actual table
     * modification work, nor for the WITH CHECK OPTIONS or RETURNING
     * expressions if any.  It would only be window dressing, since
     * ModifyTable is always a top-level node and there is no way for the
     * costs to change any higher-level planning choices.  But we might want
     * to make it look better sometime.
     */
    pathnode->path.startup_cost = 0;
    pathnode->path.total_cost = 0;
    pathnode->path.rows = 0;
    total_size = 0;
    foreach(lc, subpaths)
    {
        Path       *subpath = (Path *) lfirst(lc);

        if (lc == list_head(subpaths))  /* first node? */
            pathnode->path.startup_cost = subpath->startup_cost;
        pathnode->path.total_cost += subpath->total_cost;
        pathnode->path.rows += subpath->rows;
        total_size += subpath->pathtarget->width * subpath->rows;
    }

    /*
     * Set width to the average width of the subpath outputs.  XXX this is
     * totally wrong: we should report zero if no RETURNING, else an average
     * of the RETURNING tlist widths.  But it's what happened historically,
     * and improving it is a task for another day.
     */
    if (pathnode->path.rows > 0)
        total_size /= pathnode->path.rows;
    pathnode->path.pathtarget->width = rint(total_size);

    pathnode->operation = operation;
    pathnode->canSetTag = canSetTag;
    pathnode->nominalRelation = nominalRelation;
    pathnode->rootRelation = rootRelation;
    pathnode->partColsUpdated = partColsUpdated;
    pathnode->resultRelations = resultRelations;
    pathnode->subpaths = subpaths;
    pathnode->subroots = subroots;
    pathnode->withCheckOptionLists = withCheckOptionLists;
    pathnode->returningLists = returningLists;
    pathnode->rowMarks = rowMarks;
    pathnode->onconflict = onconflict;
    pathnode->epqParam = epqParam;

    return pathnode;
}

/*
 * create_limit_path
 *    Creates a pathnode that represents performing LIMIT/OFFSET
 *
 * In addition to providing the actual OFFSET and LIMIT expressions,
 * the caller must provide estimates of their values for costing purposes.
 * The estimates are as computed by preprocess_limit(), ie, 0 represents
 * the clause not being present, and -1 means it's present but we could
 * not estimate its value.
 *
 * 'rel' is the parent relation associated with the result
 * 'subpath' is the path representing the source of data
 * 'limitOffset' is the actual OFFSET expression, or NULL
 * 'limitCount' is the actual LIMIT expression, or NULL
 * 'offset_est' is the estimated value of the OFFSET expression
 * 'count_est' is the estimated value of the LIMIT expression
 */
LimitPath *
create_limit_path(PlannerInfo *root, RelOptInfo *rel,
                  Path *subpath,
                  Node *limitOffset, Node *limitCount,
                  LimitOption limitOption,
                  int64 offset_est, int64 count_est)
{
    LimitPath  *pathnode = makeNode(LimitPath);

    pathnode->path.pathtype = T_Limit;
    pathnode->path.parent = rel;
    /* Limit doesn't project, so use source path's pathtarget */
    pathnode->path.pathtarget = subpath->pathtarget;
    /* For now, assume we are above any joins, so no parameterization */
    pathnode->path.param_info = NULL;
    pathnode->path.parallel_aware = false;
    pathnode->path.parallel_safe = rel->consider_parallel &&
        subpath->parallel_safe;
    pathnode->path.parallel_workers = subpath->parallel_workers;
    pathnode->path.rows = subpath->rows;
    pathnode->path.startup_cost = subpath->startup_cost;
    pathnode->path.total_cost = subpath->total_cost;
    pathnode->path.pathkeys = subpath->pathkeys;
    pathnode->subpath = subpath;
    pathnode->limitOffset = limitOffset;
    pathnode->limitCount = limitCount;
    pathnode->limitOption = limitOption;

    /*
     * Adjust the output rows count and costs according to the offset/limit.
     */
    adjust_limit_rows_costs(&pathnode->path.rows,
                            &pathnode->path.startup_cost,
                            &pathnode->path.total_cost,
                            offset_est, count_est);

    return pathnode;
}

/*
 * adjust_limit_rows_costs
 *    Adjust the size and cost estimates for a LimitPath node according to the
 *    offset/limit.
 *
 * This is only a cosmetic issue if we are at top level, but if we are
 * building a subquery then it's important to report correct info to the outer
 * planner.
 *
 * When the offset or count couldn't be estimated, use 10% of the estimated
 * number of rows emitted from the subpath.
 *
 * XXX we don't bother to add eval costs of the offset/limit expressions
 * themselves to the path costs.  In theory we should, but in most cases those
 * expressions are trivial and it's just not worth the trouble.
 */
void
adjust_limit_rows_costs(double *rows,   /* in/out parameter */
                        Cost *startup_cost, /* in/out parameter */
                        Cost *total_cost,   /* in/out parameter */
                        int64 offset_est,
                        int64 count_est)
{
    double      input_rows = *rows;
    Cost        input_startup_cost = *startup_cost;
    Cost        input_total_cost = *total_cost;

    if (offset_est != 0)
    {
        double      offset_rows;

        if (offset_est > 0)
            offset_rows = (double) offset_est;
        else
            offset_rows = clamp_row_est(input_rows * 0.10);
        if (offset_rows > *rows)
            offset_rows = *rows;
        if (input_rows > 0)
            *startup_cost +=
                (input_total_cost - input_startup_cost)
                * offset_rows / input_rows;
        *rows -= offset_rows;
        if (*rows < 1)
            *rows = 1;
    }

    if (count_est != 0)
    {
        double      count_rows;

        if (count_est > 0)
            count_rows = (double) count_est;
        else
            count_rows = clamp_row_est(input_rows * 0.10);
        if (count_rows > *rows)
            count_rows = *rows;
        if (input_rows > 0)
            *total_cost = *startup_cost +
                (input_total_cost - input_startup_cost)
                * count_rows / input_rows;
        *rows = count_rows;
        if (*rows < 1)
            *rows = 1;
    }
}


/*
 * reparameterize_path
 *      Attempt to modify a Path to have greater parameterization
 *
 * We use this to attempt to bring all child paths of an appendrel to the
 * same parameterization level, ensuring that they all enforce the same set
 * of join quals (and thus that that parameterization can be attributed to
 * an append path built from such paths).  Currently, only a few path types
 * are supported here, though more could be added at need.  We return NULL
 * if we can't reparameterize the given path.
 *
 * Note: we intentionally do not pass created paths to add_path(); it would
 * possibly try to delete them on the grounds of being cost-inferior to the
 * paths they were made from, and we don't want that.  Paths made here are
 * not necessarily of general-purpose usefulness, but they can be useful
 * as members of an append path.
 */
Path *
reparameterize_path(PlannerInfo *root, Path *path,
                    Relids required_outer,
                    double loop_count)
{
    RelOptInfo *rel = path->parent;

    /* Can only increase, not decrease, path's parameterization */
    if (!bms_is_subset(PATH_REQ_OUTER(path), required_outer))
        return NULL;
    switch (path->pathtype)
    {
        case T_SeqScan:
            return create_seqscan_path(root, rel, required_outer, 0);
        case T_SampleScan:
            return (Path *) create_samplescan_path(root, rel, required_outer);
        case T_IndexScan:
        case T_IndexOnlyScan:
            {
                IndexPath  *ipath = (IndexPath *) path;
                IndexPath  *newpath = makeNode(IndexPath);

                /*
                 * We can't use create_index_path directly, and would not want
                 * to because it would re-compute the indexqual conditions
                 * which is wasted effort.  Instead we hack things a bit:
                 * flat-copy the path node, revise its param_info, and redo
                 * the cost estimate.
                 */
                memcpy(newpath, ipath, sizeof(IndexPath));
                newpath->path.param_info =
                    get_baserel_parampathinfo(root, rel, required_outer);
                cost_index(newpath, root, loop_count, false);
                return (Path *) newpath;
            }
        case T_BitmapHeapScan:
            {
                BitmapHeapPath *bpath = (BitmapHeapPath *) path;

                return (Path *) create_bitmap_heap_path(root,
                                                        rel,
                                                        bpath->bitmapqual,
                                                        required_outer,
                                                        loop_count, 0);
            }
        case T_SubqueryScan:
            {
                SubqueryScanPath *spath = (SubqueryScanPath *) path;

                return (Path *) create_subqueryscan_path(root,
                                                         rel,
                                                         spath->subpath,
                                                         spath->path.pathkeys,
                                                         required_outer);
            }
        case T_Result:
            /* Supported only for RTE_RESULT scan paths */
            if (IsA(path, Path))
                return create_resultscan_path(root, rel, required_outer);
            break;
        case T_Append:
            {
                AppendPath *apath = (AppendPath *) path;
                List       *childpaths = NIL;
                List       *partialpaths = NIL;
                int         i;
                ListCell   *lc;

                /* Reparameterize the children */
                i = 0;
                foreach(lc, apath->subpaths)
                {
                    Path       *spath = (Path *) lfirst(lc);

                    spath = reparameterize_path(root, spath,
                                                required_outer,
                                                loop_count);
                    if (spath == NULL)
                        return NULL;
                    /* We have to re-split the regular and partial paths */
                    if (i < apath->first_partial_path)
                        childpaths = lappend(childpaths, spath);
                    else
                        partialpaths = lappend(partialpaths, spath);
                    i++;
                }
                return (Path *)
                    create_append_path(root, rel, childpaths, partialpaths,
                                       apath->path.pathkeys, required_outer,
                                       apath->path.parallel_workers,
                                       apath->path.parallel_aware,
                                       apath->partitioned_rels,
                                       -1);
            }
        default:
            break;
    }
    return NULL;
}

/*
 * reparameterize_path_by_child
 *      Given a path parameterized by the parent of the given child relation,
 *      translate the path to be parameterized by the given child relation.
 *
 * The function creates a new path of the same type as the given path, but
 * parameterized by the given child relation.  Most fields from the original
 * path can simply be flat-copied, but any expressions must be adjusted to
 * refer to the correct varnos, and any paths must be recursively
 * reparameterized.  Other fields that refer to specific relids also need
 * adjustment.
 *
 * The cost, number of rows, width and parallel path properties depend upon
 * path->parent, which does not change during the translation. Hence those
 * members are copied as they are.
 *
 * If the given path can not be reparameterized, the function returns NULL.
 */
Path *
reparameterize_path_by_child(PlannerInfo *root, Path *path,
                             RelOptInfo *child_rel)
{

#define FLAT_COPY_PATH(newnode, node, nodetype)  \
    ( (newnode) = makeNode(nodetype), \
      memcpy((newnode), (node), sizeof(nodetype)) )

#define ADJUST_CHILD_ATTRS(node) \
    ((node) = \
     (List *) adjust_appendrel_attrs_multilevel(root, (Node *) (node), \
                                                child_rel->relids, \
                                                child_rel->top_parent_relids))

#define REPARAMETERIZE_CHILD_PATH(path) \
do { \
    (path) = reparameterize_path_by_child(root, (path), child_rel); \
    if ((path) == NULL) \
        return NULL; \
} while(0)

#define REPARAMETERIZE_CHILD_PATH_LIST(pathlist) \
do { \
    if ((pathlist) != NIL) \
    { \
        (pathlist) = reparameterize_pathlist_by_child(root, (pathlist), \
                                                      child_rel); \
        if ((pathlist) == NIL) \
            return NULL; \
    } \
} while(0)

    Path       *new_path;
    ParamPathInfo *new_ppi;
    ParamPathInfo *old_ppi;
    Relids      required_outer;

    /*
     * If the path is not parameterized by parent of the given relation, it
     * doesn't need reparameterization.
     */
    if (!path->param_info ||
        !bms_overlap(PATH_REQ_OUTER(path), child_rel->top_parent_relids))
        return path;

    /*
     * If possible, reparameterize the given path, making a copy.
     *
     * This function is currently only applied to the inner side of a nestloop
     * join that is being partitioned by the partitionwise-join code.  Hence,
     * we need only support path types that plausibly arise in that context.
     * (In particular, supporting sorted path types would be a waste of code
     * and cycles: even if we translated them here, they'd just lose in
     * subsequent cost comparisons.)  If we do see an unsupported path type,
     * that just means we won't be able to generate a partitionwise-join plan
     * using that path type.
     */
    switch (nodeTag(path))
    {
        case T_Path:
            FLAT_COPY_PATH(new_path, path, Path);
            break;

        case T_IndexPath:
            {
                IndexPath  *ipath;

                FLAT_COPY_PATH(ipath, path, IndexPath);
                ADJUST_CHILD_ATTRS(ipath->indexclauses);
                new_path = (Path *) ipath;
            }
            break;

        case T_BitmapHeapPath:
            {
                BitmapHeapPath *bhpath;

                FLAT_COPY_PATH(bhpath, path, BitmapHeapPath);
                REPARAMETERIZE_CHILD_PATH(bhpath->bitmapqual);
                new_path = (Path *) bhpath;
            }
            break;

        case T_BitmapAndPath:
            {
                BitmapAndPath *bapath;

                FLAT_COPY_PATH(bapath, path, BitmapAndPath);
                REPARAMETERIZE_CHILD_PATH_LIST(bapath->bitmapquals);
                new_path = (Path *) bapath;
            }
            break;

        case T_BitmapOrPath:
            {
                BitmapOrPath *bopath;

                FLAT_COPY_PATH(bopath, path, BitmapOrPath);
                REPARAMETERIZE_CHILD_PATH_LIST(bopath->bitmapquals);
                new_path = (Path *) bopath;
            }
            break;

        case T_ForeignPath:
            {
                ForeignPath *fpath;
                ReparameterizeForeignPathByChild_function rfpc_func;

                FLAT_COPY_PATH(fpath, path, ForeignPath);
                if (fpath->fdw_outerpath)
                    REPARAMETERIZE_CHILD_PATH(fpath->fdw_outerpath);

                /* Hand over to FDW if needed. */
                rfpc_func =
                    path->parent->fdwroutine->ReparameterizeForeignPathByChild;
                if (rfpc_func)
                    fpath->fdw_private = rfpc_func(root, fpath->fdw_private,
                                                   child_rel);
                new_path = (Path *) fpath;
            }
            break;

        case T_CustomPath:
            {
                CustomPath *cpath;

                FLAT_COPY_PATH(cpath, path, CustomPath);
                REPARAMETERIZE_CHILD_PATH_LIST(cpath->custom_paths);
                if (cpath->methods &&
                    cpath->methods->ReparameterizeCustomPathByChild)
                    cpath->custom_private =
                        cpath->methods->ReparameterizeCustomPathByChild(root,
                                                                        cpath->custom_private,
                                                                        child_rel);
                new_path = (Path *) cpath;
            }
            break;

        case T_NestPath:
            {
                JoinPath   *jpath;

                FLAT_COPY_PATH(jpath, path, NestPath);

                REPARAMETERIZE_CHILD_PATH(jpath->outerjoinpath);
                REPARAMETERIZE_CHILD_PATH(jpath->innerjoinpath);
                ADJUST_CHILD_ATTRS(jpath->joinrestrictinfo);
                new_path = (Path *) jpath;
            }
            break;

        case T_MergePath:
            {
                JoinPath   *jpath;
                MergePath  *mpath;

                FLAT_COPY_PATH(mpath, path, MergePath);

                jpath = (JoinPath *) mpath;
                REPARAMETERIZE_CHILD_PATH(jpath->outerjoinpath);
                REPARAMETERIZE_CHILD_PATH(jpath->innerjoinpath);
                ADJUST_CHILD_ATTRS(jpath->joinrestrictinfo);
                ADJUST_CHILD_ATTRS(mpath->path_mergeclauses);
                new_path = (Path *) mpath;
            }
            break;

        case T_HashPath:
            {
                JoinPath   *jpath;
                HashPath   *hpath;

                FLAT_COPY_PATH(hpath, path, HashPath);

                jpath = (JoinPath *) hpath;
                REPARAMETERIZE_CHILD_PATH(jpath->outerjoinpath);
                REPARAMETERIZE_CHILD_PATH(jpath->innerjoinpath);
                ADJUST_CHILD_ATTRS(jpath->joinrestrictinfo);
                ADJUST_CHILD_ATTRS(hpath->path_hashclauses);
                new_path = (Path *) hpath;
            }
            break;

        case T_AppendPath:
            {
                AppendPath *apath;

                FLAT_COPY_PATH(apath, path, AppendPath);
                REPARAMETERIZE_CHILD_PATH_LIST(apath->subpaths);
                new_path = (Path *) apath;
            }
            break;

        case T_GatherPath:
            {
                GatherPath *gpath;

                FLAT_COPY_PATH(gpath, path, GatherPath);
                REPARAMETERIZE_CHILD_PATH(gpath->subpath);
                new_path = (Path *) gpath;
            }
            break;

        default:

            /* We don't know how to reparameterize this path. */
            return NULL;
    }

    /*
     * Adjust the parameterization information, which refers to the topmost
     * parent. The topmost parent can be multiple levels away from the given
     * child, hence use multi-level expression adjustment routines.
     */
    old_ppi = new_path->param_info;
    required_outer =
        adjust_child_relids_multilevel(root, old_ppi->ppi_req_outer,
                                       child_rel->relids,
                                       child_rel->top_parent_relids);

    /* If we already have a PPI for this parameterization, just return it */
    new_ppi = find_param_path_info(new_path->parent, required_outer);

    /*
     * If not, build a new one and link it to the list of PPIs. For the same
     * reason as explained in mark_dummy_rel(), allocate new PPI in the same
     * context the given RelOptInfo is in.
     */
    if (new_ppi == NULL)
    {
        MemoryContext oldcontext;
        RelOptInfo *rel = path->parent;

        oldcontext = MemoryContextSwitchTo(GetMemoryChunkContext(rel));

        new_ppi = makeNode(ParamPathInfo);
        new_ppi->ppi_req_outer = bms_copy(required_outer);
        new_ppi->ppi_rows = old_ppi->ppi_rows;
        new_ppi->ppi_clauses = old_ppi->ppi_clauses;
        ADJUST_CHILD_ATTRS(new_ppi->ppi_clauses);
        rel->ppilist = lappend(rel->ppilist, new_ppi);

        MemoryContextSwitchTo(oldcontext);
    }
    bms_free(required_outer);

    new_path->param_info = new_ppi;

    /*
     * Adjust the path target if the parent of the outer relation is
     * referenced in the targetlist. This can happen when only the parent of
     * outer relation is laterally referenced in this relation.
     */
    if (bms_overlap(path->parent->lateral_relids,
                    child_rel->top_parent_relids))
    {
        new_path->pathtarget = copy_pathtarget(new_path->pathtarget);
        ADJUST_CHILD_ATTRS(new_path->pathtarget->exprs);
    }

    return new_path;
}

/*
 * reparameterize_pathlist_by_child
 *      Helper function to reparameterize a list of paths by given child rel.
 */
static List *
reparameterize_pathlist_by_child(PlannerInfo *root,
                                 List *pathlist,
                                 RelOptInfo *child_rel)
{
    ListCell   *lc;
    List       *result = NIL;

    foreach(lc, pathlist)
    {
        Path       *path = reparameterize_path_by_child(root, lfirst(lc),
                                                        child_rel);

        if (path == NULL)
        {
            list_free(result);
            return NIL;
        }

        result = lappend(result, path);
    }

    return result;
}