pathnode.c

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/*-------------------------------------------------------------------------
 *
 * pathnode.c
 *    Routines to manipulate pathlists and create path nodes
 *
 * Portions Copyright (c) 1996-2026, 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 "access/htup_details.h"
#include "executor/nodeSetOp.h"
#include "foreign/fdwapi.h"
#include "miscadmin.h"
#include "nodes/extensible.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/tlist.h"
#include "parser/parsetree.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 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);
static bool pathlist_is_reparameterizable_by_child(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)
{
    /* Number of disabled nodes, if different, trumps all else. */
    if (unlikely(path1->disabled_nodes != path2->disabled_nodes))
    {
        if (path1->disabled_nodes < path2->disabled_nodes)
            return -1;
        else
            return +1;
    }
 
    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_fractional_path_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;
 
    /* Number of disabled nodes, if different, trumps all else. */
    if (unlikely(path1->disabled_nodes != path2->disabled_nodes))
    {
        if (path1->disabled_nodes < path2->disabled_nodes)
            return -1;
        else
            return +1;
    }
 
    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)
 
    /* Number of disabled nodes, if different, trumps all else. */
    if (unlikely(path1->disabled_nodes != path2->disabled_nodes))
    {
        if (path1->disabled_nodes < path2->disabled_nodes)
            return COSTS_BETTER1;
        else
            return COSTS_BETTER2;
    }
 
    /*
     * 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_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 (as defined below), 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.
 *
 *    Cheaper cost can mean either a cheaper total cost or a cheaper startup
 *    cost; if one path is cheaper in one of these aspects and another is
 *    cheaper in the other, we keep both. However, when some path type is
 *    disabled (e.g. due to enable_seqscan=false), the number of times that
 *    a disabled path type is used is considered to be a higher-order
 *    component of the cost. Hence, if path A uses no disabled path type,
 *    and path B uses 1 or more disabled path types, A is cheaper, no matter
 *    what we estimate for the startup and total costs. The startup and total
 *    cost essentially act as a tiebreak when comparing paths that use equal
 *    numbers of disabled path nodes; but in practice this tiebreak is almost
 *    always used, since normally no path types are disabled.
 *
 *    In addition to possibly adding new_path, 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 disabled_nodes and then 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 more disabled nodes
             * or if it has the same number of nodes but a greater total cost
             */
            if (new_path->disabled_nodes > old_path->disabled_nodes ||
                (new_path->disabled_nodes == old_path->disabled_nodes &&
                 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, int disabled_nodes,
                  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;
 
        /*
         * Since the pathlist is sorted by disabled_nodes and then by
         * total_cost, we can stop looking once we reach a path with more
         * disabled nodes, or the same number of disabled nodes plus a
         * total_cost larger than the new path's.
         */
        if (unlikely(old_path->disabled_nodes != disabled_nodes))
        {
            if (disabled_nodes < old_path->disabled_nodes)
                break;
        }
        else if (total_cost <= old_path->total_cost * STD_FUZZ_FACTOR)
            break;
 
        /*
         * 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.
         */
        /* 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;
                }
            }
        }
    }
 
    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 first by smallest
 *    number of disabled nodes and then by lowest total cost. 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.  However, we do need to consider the
 *    startup costs: this partial path could be used beneath a Limit node,
 *    so a fast-start plan could be correct.
 *
 *    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, see if one of the paths dominates
         * the other (both in startup and total cost). It may happen that one
         * path has lower startup cost, the other has lower total cost.
         */
        if (keyscmp != PATHKEYS_DIFFERENT)
        {
            PathCostComparison costcmp;
 
            /*
             * Do a fuzzy cost comparison with standard fuzziness limit.
             */
            costcmp = compare_path_costs_fuzzily(new_path, old_path,
                                                 STD_FUZZ_FACTOR);
            if (costcmp == COSTS_BETTER1)
            {
                if (keyscmp != PATHKEYS_BETTER2)
                    remove_old = true;
            }
            else if (costcmp == COSTS_BETTER2)
            {
                if (keyscmp != PATHKEYS_BETTER1)
                    accept_new = false;
            }
            else if (costcmp == COSTS_EQUAL)
            {
                if (keyscmp == PATHKEYS_BETTER1)
                    remove_old = true;
                else if (keyscmp == PATHKEYS_BETTER2)
                    accept_new = false;
                else if (compare_path_costs_fuzzily(new_path, old_path,
                                                    1.0000000001) == COSTS_BETTER1)
                    remove_old = true;
                else
                    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 more disabled nodes
             * or if it has the same number of nodes but a greater total cost
             */
            if (new_path->disabled_nodes > old_path->disabled_nodes ||
                (new_path->disabled_nodes == old_path->disabled_nodes &&
                 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 parameterization, since it doesn'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, int disabled_nodes,
                          Cost startup_cost, Cost total_cost, List *pathkeys)
{
    bool        consider_startup = parent_rel->consider_startup;
    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 never try to exit this loop early. 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);
        PathCostComparison costcmp;
        PathKeysComparison keyscmp;
 
        /*
         * First, compare costs and disabled nodes. This logic should be
         * identical to compare_path_costs_fuzzily, except that one of the
         * paths hasn't been created yet, and the fuzz factor is always
         * STD_FUZZ_FACTOR.
         */
        if (unlikely(old_path->disabled_nodes != disabled_nodes))
        {
            if (disabled_nodes < old_path->disabled_nodes)
                costcmp = COSTS_BETTER1;
            else
                costcmp = COSTS_BETTER2;
        }
        else if (total_cost > old_path->total_cost * STD_FUZZ_FACTOR)
        {
            if (consider_startup &&
                old_path->startup_cost > startup_cost * STD_FUZZ_FACTOR)
                costcmp = COSTS_DIFFERENT;
            else
                costcmp = COSTS_BETTER2;
        }
        else if (old_path->total_cost > total_cost * STD_FUZZ_FACTOR)
        {
            if (consider_startup &&
                startup_cost > old_path->startup_cost * STD_FUZZ_FACTOR)
                costcmp = COSTS_DIFFERENT;
            else
                costcmp = COSTS_BETTER1;
        }
        else if (startup_cost > old_path->startup_cost * STD_FUZZ_FACTOR)
            costcmp = COSTS_BETTER2;
        else if (old_path->startup_cost > startup_cost * STD_FUZZ_FACTOR)
            costcmp = COSTS_BETTER1;
        else
            costcmp = COSTS_EQUAL;
 
        /*
         * If one path wins on startup cost and the other on total cost, we
         * can't say for sure which is better.
         */
        if (costcmp == COSTS_DIFFERENT)
            continue;
 
        /*
         * If the two paths have different pathkeys, we can't say for sure
         * which is better.
         */
        keyscmp = compare_pathkeys(pathkeys, old_path->pathkeys);
        if (keyscmp == PATHKEYS_DIFFERENT)
            continue;
 
        /*
         * If the existing path is cheaper and the pathkeys are equal or
         * worse, the new path is not interesting.
         */
        if (costcmp == COSTS_BETTER2 && keyscmp != PATHKEYS_BETTER1)
            return false;
 
        /*
         * If the new path is cheaper and the pathkeys are equal or better, it
         * is definitely interesting.
         */
        if (costcmp == COSTS_BETTER1 && 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.
     */
    if (!add_path_precheck(parent_rel, disabled_nodes, startup_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);
    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 either ForwardScanDirection or BackwardScanDirection.
 * '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);
 
    /*
     * cost_index will set disabled_nodes to 1 if this rel is not allowed to
     * use index scans in general, but it doesn't have the IndexOptInfo to
     * know whether this specific index has been disabled.
     */
    if (index->disabled)
        pathnode->path.disabled_nodes = 1;
 
    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);
    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_tidrangescan_path
 *    Creates a path corresponding to a scan by a range of TIDs, returning
 *    the pathnode.
 */
TidRangePath *
create_tidrangescan_path(PlannerInfo *root, RelOptInfo *rel,
                         List *tidrangequals, Relids required_outer,
                         int parallel_workers)
{
    TidRangePath *pathnode = makeNode(TidRangePath);
 
    pathnode->path.pathtype = T_TidRangeScan;
    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_workers > 0);
    pathnode->path.parallel_safe = rel->consider_parallel;
    pathnode->path.parallel_workers = parallel_workers;
    pathnode->path.pathkeys = NIL;  /* always unordered */
 
    pathnode->tidrangequals = tidrangequals;
 
    cost_tidrangescan(&pathnode->path, root, rel, tidrangequals,
                      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.
 *
 * 'rows', when passed as a non-negative number, will be used to overwrite the
 * returned path's row estimate.  Otherwise, the row estimate is calculated
 * by totalling the row estimates from the 'subpaths' list.
 */
AppendPath *
create_append_path(PlannerInfo *root,
                   RelOptInfo *rel,
                   AppendPathInput input,
                   List *pathkeys, Relids required_outer,
                   int parallel_workers, bool parallel_aware,
                   double rows)
{
    AppendPath *pathnode = makeNode(AppendPath);
    ListCell   *l;
 
    Assert(!parallel_aware || parallel_workers > 0);
 
    pathnode->child_append_relid_sets = input.child_append_relid_sets;
    pathnode->path.pathtype = T_Append;
    pathnode->path.parent = rel;
    pathnode->path.pathtarget = rel->reltarget;
 
    /*
     * If this is for a baserel (not a join or non-leaf partition), we prefer
     * to apply get_baserel_parampathinfo to construct a full ParamPathInfo
     * for the path.  This supports building a Memoize path atop this path,
     * and if this is a partitioned table the info may be useful for run-time
     * pruning (cf make_partition_pruneinfo()).
     *
     * However, if we don't have "root" then that won't work and we fall back
     * on the simpler get_appendrel_parampathinfo.  There's no point in doing
     * the more expensive thing for a dummy path, either.
     */
    if (rel->reloptkind == RELOPT_BASEREL && root && input.subpaths != NIL)
        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;
 
    /*
     * 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(input.subpaths, append_total_cost_compare);
        list_sort(input.partial_subpaths, append_startup_cost_compare);
    }
    pathnode->first_partial_path = list_length(input.subpaths);
    pathnode->subpaths = list_concat(input.subpaths, input.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_query_rels))
        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 then the output of the Append is
     * necessarily ordered the same as the child's, so we can inherit the
     * child's pathkeys if any, overriding whatever the caller might've said.
     * Furthermore, if the child's parallel awareness matches the Append's,
     * then the Append is a no-op and will be discarded later (in setrefs.c).
     * Then we can inherit the child's size and cost too, effectively charging
     * zero for the Append.  Otherwise, we must do the normal costsize
     * calculation.
     */
    if (list_length(pathnode->subpaths) == 1)
    {
        Path       *child = (Path *) linitial(pathnode->subpaths);
 
        if (child->parallel_aware == parallel_aware)
        {
            pathnode->path.rows = child->rows;
            pathnode->path.startup_cost = child->startup_cost;
            pathnode->path.total_cost = child->total_cost;
        }
        else
            cost_append(pathnode, root);
        /* Must do this last, else cost_append complains */
        pathnode->path.pathkeys = child->pathkeys;
    }
    else
        cost_append(pathnode, root);
 
    /* 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 *child_append_relid_sets,
                         List *pathkeys,
                         Relids required_outer)
{
    MergeAppendPath *pathnode = makeNode(MergeAppendPath);
    int         input_disabled_nodes;
    Cost        input_startup_cost;
    Cost        input_total_cost;
    ListCell   *l;
 
    /*
     * We don't currently support parameterized MergeAppend paths, as
     * explained in the comments for generate_orderedappend_paths.
     */
    Assert(bms_is_empty(rel->lateral_relids) && bms_is_empty(required_outer));
 
    pathnode->child_append_relid_sets = child_append_relid_sets;
    pathnode->path.pathtype = T_MergeAppend;
    pathnode->path.parent = rel;
    pathnode->path.pathtarget = 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.pathkeys = pathkeys;
    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_query_rels))
        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_disabled_nodes = 0;
    input_startup_cost = 0;
    input_total_cost = 0;
    foreach(l, subpaths)
    {
        Path       *subpath = (Path *) lfirst(l);
        int         presorted_keys;
        Path        sort_path;  /* dummy for result of
                                 * cost_sort/cost_incremental_sort */
 
        /* All child paths should be unparameterized */
        Assert(bms_is_empty(PATH_REQ_OUTER(subpath)));
 
        pathnode->path.rows += subpath->rows;
        pathnode->path.parallel_safe = pathnode->path.parallel_safe &&
            subpath->parallel_safe;
 
        if (!pathkeys_count_contained_in(pathkeys, subpath->pathkeys,
                                         &presorted_keys))
        {
            /*
             * We'll need to insert a Sort node, so include costs for that. We
             * choose to use incremental sort if it is enabled and there are
             * presorted keys; otherwise we use full sort.
             *
             * We can use the parent's LIMIT if any, since we certainly won't
             * pull more than that many tuples from any child.
             */
            if (enable_incremental_sort && presorted_keys > 0)
            {
                cost_incremental_sort(&sort_path,
                                      root,
                                      pathkeys,
                                      presorted_keys,
                                      subpath->disabled_nodes,
                                      subpath->startup_cost,
                                      subpath->total_cost,
                                      subpath->rows,
                                      subpath->pathtarget->width,
                                      0.0,
                                      work_mem,
                                      pathnode->limit_tuples);
            }
            else
            {
                cost_sort(&sort_path,
                          root,
                          pathkeys,
                          subpath->disabled_nodes,
                          subpath->total_cost,
                          subpath->rows,
                          subpath->pathtarget->width,
                          0.0,
                          work_mem,
                          pathnode->limit_tuples);
            }
 
            subpath = &sort_path;
        }
 
        input_disabled_nodes += subpath->disabled_nodes;
        input_startup_cost += subpath->startup_cost;
        input_total_cost += subpath->total_cost;
    }
 
    /*
     * Now we can compute total costs of the MergeAppend.  If there's exactly
     * one child path and its parallel awareness matches that of the
     * MergeAppend, then 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 &&
        ((Path *) linitial(subpaths))->parallel_aware ==
        pathnode->path.parallel_aware)
    {
        pathnode->path.disabled_nodes = input_disabled_nodes;
        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_disabled_nodes,
                          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, bool enabled)
{
    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,
                  enabled,
                  subpath->disabled_nodes,
                  subpath->startup_cost,
                  subpath->total_cost,
                  subpath->rows,
                  subpath->pathtarget->width);
 
    return pathnode;
}
 
/*
 * create_memoize_path
 *    Creates a path corresponding to a Memoize plan, returning the pathnode.
 */
MemoizePath *
create_memoize_path(PlannerInfo *root, RelOptInfo *rel, Path *subpath,
                    List *param_exprs, List *hash_operators,
                    bool singlerow, bool binary_mode, Cardinality est_calls)
{
    MemoizePath *pathnode = makeNode(MemoizePath);
 
    Assert(subpath->parent == rel);
 
    pathnode->path.pathtype = T_Memoize;
    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;
    pathnode->hash_operators = hash_operators;
    pathnode->param_exprs = param_exprs;
    pathnode->singlerow = singlerow;
    pathnode->binary_mode = binary_mode;
 
    /*
     * For now we set est_entries to 0.  cost_memoize_rescan() does all the
     * hard work to determine how many cache entries there are likely to be,
     * so it seems best to leave it up to that function to fill this field in.
     * If left at 0, the executor will make a guess at a good value.
     */
    pathnode->est_entries = 0;
 
    pathnode->est_calls = clamp_row_est(est_calls);
 
    /* These will also be set later in cost_memoize_rescan() */
    pathnode->est_unique_keys = 0.0;
    pathnode->est_hit_ratio = 0.0;
 
    /*
     * We should not be asked to generate this path type when memoization is
     * disabled, so set our count of disabled nodes equal to the subpath's
     * count.
     *
     * It would be nice to also Assert that memoization is enabled, but the
     * value of enable_memoize is not controlling: what we would need to check
     * is that the JoinPathExtraData's pgs_mask included PGS_NESTLOOP_MEMOIZE.
     */
    pathnode->path.disabled_nodes = subpath->disabled_nodes;
 
    /*
     * Add a small additional charge for caching the first entry.  All the
     * harder calculations for rescans are performed in cost_memoize_rescan().
     */
    pathnode->path.startup_cost = subpath->startup_cost + cpu_tuple_cost;
    pathnode->path.total_cost = subpath->total_cost + cpu_tuple_cost;
    pathnode->path.rows = subpath->rows;
 
    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);
    int         input_disabled_nodes = 0;
    Cost        input_startup_cost = 0;
    Cost        input_total_cost = 0;
 
    Assert(subpath->parallel_safe);
    Assert(pathkeys);
 
    /*
     * The subpath should guarantee that it is adequately ordered either by
     * adding an explicit sort node or by using presorted input.  We cannot
     * add an explicit Sort node for the subpath in createplan.c on additional
     * pathkeys, because we can't guarantee the sort would be safe.  For
     * example, expressions may be volatile or otherwise parallel unsafe.
     */
    if (!pathkeys_contained_in(pathkeys, subpath->pathkeys))
        elog(ERROR, "gather merge input not sufficiently sorted");
 
    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;
 
    input_disabled_nodes += subpath->disabled_nodes;
    input_startup_cost += subpath->startup_cost;
    input_total_cost += subpath->total_cost;
 
    cost_gather_merge(pathnode, root, rel, pathnode->path.param_info,
                      input_disabled_nodes, input_startup_cost,
                      input_total_cost, rows);
 
    return pathnode;
}
 
/*
 * 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.
 *
 * Caller must pass trivial_pathtarget = true if it believes rel->reltarget to
 * be trivial, ie just a fetch of all the subquery output columns in order.
 * While we could determine that here, the caller can usually do it more
 * efficiently (or at least amortize it over multiple calls).
 */
SubqueryScanPath *
create_subqueryscan_path(PlannerInfo *root, RelOptInfo *rel, Path *subpath,
                         bool trivial_pathtarget,
                         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,
                      trivial_pathtarget);
 
    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,
                    List *pathkeys, 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 = pathkeys;
 
    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, int disabled_nodes,
                        Cost startup_cost, Cost total_cost,
                        List *pathkeys,
                        Relids required_outer,
                        Path *fdw_outerpath,
                        List *fdw_restrictinfo,
                        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.disabled_nodes = disabled_nodes;
    pathnode->path.startup_cost = startup_cost;
    pathnode->path.total_cost = total_cost;
    pathnode->path.pathkeys = pathkeys;
 
    pathnode->fdw_outerpath = fdw_outerpath;
    pathnode->fdw_restrictinfo = fdw_restrictinfo;
    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, int disabled_nodes,
                         Cost startup_cost, Cost total_cost,
                         List *pathkeys,
                         Relids required_outer,
                         Path *fdw_outerpath,
                         List *fdw_restrictinfo,
                         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.disabled_nodes = disabled_nodes;
    pathnode->path.startup_cost = startup_cost;
    pathnode->path.total_cost = total_cost;
    pathnode->path.pathkeys = pathkeys;
 
    pathnode->fdw_outerpath = fdw_outerpath;
    pathnode->fdw_restrictinfo = fdw_restrictinfo;
    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, int disabled_nodes,
                          Cost startup_cost, Cost total_cost,
                          List *pathkeys,
                          Path *fdw_outerpath,
                          List *fdw_restrictinfo,
                          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.disabled_nodes = disabled_nodes;
    pathnode->path.startup_cost = startup_cost;
    pathnode->path.total_cost = total_cost;
    pathnode->path.pathkeys = pathkeys;
 
    pathnode->fdw_outerpath = fdw_outerpath;
    pathnode->fdw_restrictinfo = fdw_restrictinfo;
    pathnode->fdw_private = fdw_private;
 
    return pathnode;
}
 
/*
 * calc_nestloop_required_outer
 *    Compute the required_outer set for a nestloop join path
 *
 * Note: when considering a child join, the inputs nonetheless use top-level
 * parent relids
 *
 * 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);
    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      innerrelids PG_USED_FOR_ASSERTS_ONLY;
    Relids      outerrelids PG_USED_FOR_ASSERTS_ONLY;
    Relids      required_outer;
 
    /*
     * Any parameterization of the input paths refers to topmost parents of
     * the relevant relations, because reparameterize_path_by_child() hasn't
     * been called yet.  So we must consider topmost parents of the relations
     * being joined, too, while checking for disallowed parameterization
     * cases.
     */
    if (inner_path->parent->top_parent_relids)
        innerrelids = inner_path->parent->top_parent_relids;
    else
        innerrelids = inner_path->parent->relids;
 
    if (outer_path->parent->top_parent_relids)
        outerrelids = outer_path->parent->top_parent_relids;
    else
        outerrelids = outer_path->parent->relids;
 
    /* neither path can require rels from the other */
    Assert(!bms_overlap(outer_paramrels, innerrelids));
    Assert(!bms_overlap(inner_paramrels, outerrelids));
    /* 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);
    Relids      outerrelids;
 
    /*
     * Paths are parameterized by top-level parents, so run parameterization
     * tests on the parent relids.
     */
    if (outer_path->parent->top_parent_relids)
        outerrelids = outer_path->parent->top_parent_relids;
    else
        outerrelids = outer_path->parent->relids;
 
    /*
     * 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.  We detect such clauses by checking for serial
     * number match to clauses already enforced in the inner path.
     */
    if (bms_overlap(inner_req_outer, outerrelids))
    {
        Bitmapset  *enforced_serials = get_param_path_clause_serials(inner_path);
        List       *jclauses = NIL;
        ListCell   *lc;
 
        foreach(lc, restrict_clauses)
        {
            RestrictInfo *rinfo = (RestrictInfo *) lfirst(lc);
 
            if (!bms_is_member(rinfo->rinfo_serial, enforced_serials))
                jclauses = lappend(jclauses, rinfo);
        }
        restrict_clauses = jclauses;
    }
 
    pathnode->jpath.path.pathtype = T_NestLoop;
    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;
 
    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
 * 'outer_presorted_keys' is the number of presorted keys of the outer path
 */
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,
                      int outer_presorted_keys)
{
    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->outer_presorted_keys = outer_presorted_keys;
    /* 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;
 
    /*
     * We mustn't put a ProjectionPath directly above another; it's useless
     * and will confuse create_projection_plan.  Rather than making sure all
     * callers handle that, let's implement it here, by stripping off any
     * ProjectionPath in what we're given.  Given this rule, there won't be
     * more than one.
     */
    if (IsA(subpath, ProjectionPath))
    {
        ProjectionPath *subpp = (ProjectionPath *) subpath;
 
        Assert(subpp->path.parent == rel);
        subpath = subpp->subpath;
        Assert(!IsA(subpath, ProjectionPath));
    }
 
    pathnode->path.pathtype = T_Result;
    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 &&
        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.
     */
    oldtarget = subpath->pathtarget;
    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.disabled_nodes = subpath->disabled_nodes;
        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.disabled_nodes = subpath->disabled_nodes;
        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.disabled_nodes = subpath->disabled_nodes;
    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
 */
IncrementalSortPath *
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;
    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 = pathkeys;
 
    pathnode->subpath = subpath;
 
    cost_incremental_sort(&pathnode->path,
                          root, pathkeys, presorted_keys,
                          subpath->disabled_nodes,
                          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 sort;
}
 
/*
 * 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;
    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 = pathkeys;
 
    pathnode->subpath = subpath;
 
    cost_sort(&pathnode->path, root, pathkeys,
              subpath->disabled_nodes,
              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->disabled_nodes,
               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_unique_path
 *    Creates a pathnode that represents performing an explicit Unique step
 *    on presorted input.
 *
 * '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
 */
UniquePath *
create_unique_path(PlannerInfo *root,
                   RelOptInfo *rel,
                   Path *subpath,
                   int numCols,
                   double numGroups)
{
    UniquePath *pathnode = makeNode(UniquePath);
 
    pathnode->path.pathtype = T_Unique;
    pathnode->path.parent = rel;
    /* Unique doesn't project, so use source path's pathtarget */
    pathnode->path.pathtarget = subpath->pathtarget;
    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;
    /* 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.disabled_nodes = subpath->disabled_nodes;
    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;
    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;
 
    if (aggstrategy == AGG_SORTED)
    {
        /*
         * Attempt to preserve the order of the subpath.  Additional pathkeys
         * may have been added in adjust_group_pathkeys_for_groupagg() to
         * support ORDER BY / DISTINCT aggregates.  Pathkeys added there
         * belong to columns within the aggregate function, so we must strip
         * these additional pathkeys off as those columns are unavailable
         * above the aggregate node.
         */
        if (list_length(subpath->pathkeys) > root->num_groupby_pathkeys)
            pathnode->path.pathkeys = list_copy_head(subpath->pathkeys,
                                                     root->num_groupby_pathkeys);
        else
            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->disabled_nodes,
             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
 */
GroupingSetsPath *
create_groupingsets_path(PlannerInfo *root,
                         RelOptInfo *rel,
                         Path *subpath,
                         List *having_qual,
                         AggStrategy aggstrategy,
                         List *rollups,
                         const AggClauseCosts *agg_costs)
{
    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->disabled_nodes,
                     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, 0.0,
                         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,
                          0.0,
                          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.disabled_nodes,
                         sort_path.startup_cost,
                         sort_path.total_cost,
                         sort_path.rows,
                         subpath->pathtarget->width);
            }
 
            pathnode->path.disabled_nodes += agg_path.disabled_nodes;
            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;
    int         initplan_disabled_nodes = 0;
    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;
    pathnode->path.parallel_safe = true;    /* might change below */
    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, and check parallel safety */
    initplan_cost = 0;
    foreach(lc, mmaggregates)
    {
        MinMaxAggInfo *mminfo = (MinMaxAggInfo *) lfirst(lc);
 
        initplan_disabled_nodes += mminfo->path->disabled_nodes;
        initplan_cost += mminfo->pathcost;
        if (!mminfo->path->parallel_safe)
            pathnode->path.parallel_safe = false;
    }
 
    /* add tlist eval cost for each output row, plus cpu_tuple_cost */
    pathnode->path.disabled_nodes = initplan_disabled_nodes;
    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;
    }
 
    /*
     * If the initplans were all parallel-safe, also check safety of the
     * target and quals.  (The Result node itself isn't parallelizable, but if
     * we are in a subquery then it can be useful for the outer query to know
     * that this one is parallel-safe.)
     */
    if (pathnode->path.parallel_safe)
        pathnode->path.parallel_safe =
            is_parallel_safe(root, (Node *) target->exprs) &&
            is_parallel_safe(root, (Node *) quals);
 
    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
 * 'runCondition' is a list of OpExprs to short-circuit WindowAgg execution
 * 'winclause' is a WindowClause that is common to all the WindowFuncs
 * 'qual' WindowClause.runconditions from lower-level WindowAggPaths.
 *      Must always be NIL when topwindow == false
 * 'topwindow' pass as true only for the top-level WindowAgg. False for all
 *      intermediate WindowAggs.
 *
 * 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,
                      List *runCondition,
                      WindowClause *winclause,
                      List *qual,
                      bool topwindow)
{
    WindowAggPath *pathnode = makeNode(WindowAggPath);
 
    /* qual can only be set for the topwindow */
    Assert(qual == NIL || topwindow);
 
    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;
    pathnode->qual = qual;
    pathnode->runCondition = runCondition;
    pathnode->topwindow = topwindow;
 
    /*
     * 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,
                   winclause,
                   subpath->disabled_nodes,
                   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
 * 'leftpath' is the path representing the left-hand source of data
 * 'rightpath' is the path representing the right-hand source of data
 * 'cmd' is the specific semantics (INTERSECT or EXCEPT, with/without ALL)
 * 'strategy' is the implementation strategy (sorted or hashed)
 * 'groupList' is a list of SortGroupClause's representing the grouping
 * 'numGroups' is the estimated number of distinct groups in left-hand input
 * 'outputRows' is the estimated number of output rows
 *
 * leftpath and rightpath must produce the same columns.  Moreover, if
 * strategy is SETOP_SORTED, leftpath and rightpath must both be sorted
 * by all the grouping columns.
 */
SetOpPath *
create_setop_path(PlannerInfo *root,
                  RelOptInfo *rel,
                  Path *leftpath,
                  Path *rightpath,
                  SetOpCmd cmd,
                  SetOpStrategy strategy,
                  List *groupList,
                  double numGroups,
                  double outputRows)
{
    SetOpPath  *pathnode = makeNode(SetOpPath);
 
    pathnode->path.pathtype = T_SetOp;
    pathnode->path.parent = rel;
    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 = rel->consider_parallel &&
        leftpath->parallel_safe && rightpath->parallel_safe;
    pathnode->path.parallel_workers =
        leftpath->parallel_workers + rightpath->parallel_workers;
    /* SetOp preserves the input sort order if in sort mode */
    pathnode->path.pathkeys =
        (strategy == SETOP_SORTED) ? leftpath->pathkeys : NIL;
 
    pathnode->leftpath = leftpath;
    pathnode->rightpath = rightpath;
    pathnode->cmd = cmd;
    pathnode->strategy = strategy;
    pathnode->groupList = groupList;
    pathnode->numGroups = numGroups;
 
    /*
     * Compute cost estimates.  As things stand, we end up with the same total
     * cost in this node for sort and hash methods, but different startup
     * costs.  This could be refined perhaps, but it'll do for now.
     */
    pathnode->path.disabled_nodes =
        leftpath->disabled_nodes + rightpath->disabled_nodes;
    if (strategy == SETOP_SORTED)
    {
        /*
         * In sorted mode, we can emit output incrementally.  Charge one
         * cpu_operator_cost per comparison per input tuple.  Like cost_group,
         * we assume all columns get compared at most of the tuples.
         */
        pathnode->path.startup_cost =
            leftpath->startup_cost + rightpath->startup_cost;
        pathnode->path.total_cost =
            leftpath->total_cost + rightpath->total_cost +
            cpu_operator_cost * (leftpath->rows + rightpath->rows) * list_length(groupList);
 
        /*
         * Also charge a small amount per extracted tuple.  Like cost_sort,
         * charge only operator cost not cpu_tuple_cost, since SetOp does no
         * qual-checking or projection.
         */
        pathnode->path.total_cost += cpu_operator_cost * outputRows;
    }
    else
    {
        Size        hashtablesize;
 
        /*
         * In hashed mode, we must read all the input before we can emit
         * anything.  Also charge comparison costs to represent the cost of
         * hash table lookups.
         */
        pathnode->path.startup_cost =
            leftpath->total_cost + rightpath->total_cost +
            cpu_operator_cost * (leftpath->rows + rightpath->rows) * list_length(groupList);
        pathnode->path.total_cost = pathnode->path.startup_cost;
 
        /*
         * Also charge a small amount per extracted tuple.  Like cost_sort,
         * charge only operator cost not cpu_tuple_cost, since SetOp does no
         * qual-checking or projection.
         */
        pathnode->path.total_cost += cpu_operator_cost * outputRows;
 
        /*
         * Mark the path as disabled if enable_hashagg is off.  While this
         * isn't exactly a HashAgg node, it seems close enough to justify
         * letting that switch control it.
         */
        if (!enable_hashagg)
            pathnode->path.disabled_nodes++;
 
        /*
         * Also disable if it doesn't look like the hashtable will fit into
         * hash_mem.  (Note: reject on equality, to ensure that an estimate of
         * SIZE_MAX disables hashing regardless of the hash_mem limit.)
         */
        hashtablesize = EstimateSetOpHashTableSpace(numGroups,
                                                    leftpath->pathtarget->width);
        if (hashtablesize >= get_hash_memory_limit())
            pathnode->path.disabled_nodes++;
    }
    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.disabled_nodes = subpath->disabled_nodes;
    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/MERGE
 *    mods
 *
 * 'rel' is the parent relation associated with the result
 * 'subpath' is a Path producing source data
 * '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/inherited table root RTI, or 0 if none
 * 'resultRelations' is an integer list of actual RT indexes of target rel(s)
 * 'updateColnosLists' is a list of UPDATE target column number lists
 *      (one sublist per rel); or NIL if not an UPDATE
 * '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
 * 'mergeActionLists' is a list of lists of MERGE actions (one per rel)
 * 'mergeJoinConditions' is a list of join conditions for MERGE (one per rel)
 */
ModifyTablePath *
create_modifytable_path(PlannerInfo *root, RelOptInfo *rel,
                        Path *subpath,
                        CmdType operation, bool canSetTag,
                        Index nominalRelation, Index rootRelation,
                        List *resultRelations,
                        List *updateColnosLists,
                        List *withCheckOptionLists, List *returningLists,
                        List *rowMarks, OnConflictExpr *onconflict,
                        List *mergeActionLists, List *mergeJoinConditions,
                        int epqParam)
{
    ModifyTablePath *pathnode = makeNode(ModifyTablePath);
 
    Assert(operation == CMD_MERGE ||
           (operation == CMD_UPDATE ?
            list_length(resultRelations) == list_length(updateColnosLists) :
            updateColnosLists == NIL));
    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 subpath cost & rowcount (if RETURNING)
     *
     * 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.disabled_nodes = subpath->disabled_nodes;
    pathnode->path.startup_cost = subpath->startup_cost;
    pathnode->path.total_cost = subpath->total_cost;
    if (returningLists != NIL)
    {
        pathnode->path.rows = subpath->rows;
 
        /*
         * Set width to match the subpath output.  XXX this is totally wrong:
         * we should return an average of the RETURNING tlist widths.  But
         * it's what happened historically, and improving it is a task for
         * another day.  (Again, it's mostly window dressing.)
         */
        pathnode->path.pathtarget->width = subpath->pathtarget->width;
    }
    else
    {
        pathnode->path.rows = 0;
        pathnode->path.pathtarget->width = 0;
    }
 
    pathnode->subpath = subpath;
    pathnode->operation = operation;
    pathnode->canSetTag = canSetTag;
    pathnode->nominalRelation = nominalRelation;
    pathnode->rootRelation = rootRelation;
    pathnode->resultRelations = resultRelations;
    pathnode->updateColnosLists = updateColnosLists;
    pathnode->withCheckOptionLists = withCheckOptionLists;
    pathnode->returningLists = returningLists;
    pathnode->rowMarks = rowMarks;
    pathnode->onconflict = onconflict;
    pathnode->epqParam = epqParam;
    pathnode->mergeActionLists = mergeActionLists;
    pathnode->mergeJoinConditions = mergeJoinConditions;
 
    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.disabled_nodes = subpath->disabled_nodes;
    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 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;
                Path       *subpath = spath->subpath;
                bool        trivial_pathtarget;
 
                /*
                 * If existing node has zero extra cost, we must have decided
                 * its target is trivial.  (The converse is not true, because
                 * it might have a trivial target but quals to enforce; but in
                 * that case the new node will too, so it doesn't matter
                 * whether we get the right answer here.)
                 */
                trivial_pathtarget =
                    (subpath->total_cost == spath->path.total_cost);
 
                return (Path *) create_subqueryscan_path(root,
                                                         rel,
                                                         subpath,
                                                         trivial_pathtarget,
                                                         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;
                AppendPathInput new_append = {0};
                int         i;
                ListCell   *lc;
 
                new_append.child_append_relid_sets = apath->child_append_relid_sets;
 
                /* 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)
                        new_append.subpaths = lappend(new_append.subpaths, spath);
                    else
                        new_append.partial_subpaths = lappend(new_append.partial_subpaths, spath);
                    i++;
                }
                return (Path *)
                    create_append_path(root, rel, new_append,
                                       apath->path.pathkeys, required_outer,
                                       apath->path.parallel_workers,
                                       apath->path.parallel_aware,
                                       -1);
            }
        case T_Material:
            {
                MaterialPath *mpath = (MaterialPath *) path;
                Path       *spath = mpath->subpath;
                bool        enabled;
 
                spath = reparameterize_path(root, spath,
                                            required_outer,
                                            loop_count);
                if (spath == NULL)
                    return NULL;
                enabled =
                    (mpath->path.disabled_nodes <= spath->disabled_nodes);
                return (Path *) create_material_path(rel, spath, enabled);
            }
        case T_Memoize:
            {
                MemoizePath *mpath = (MemoizePath *) path;
                Path       *spath = mpath->subpath;
 
                spath = reparameterize_path(root, spath,
                                            required_outer,
                                            loop_count);
                if (spath == NULL)
                    return NULL;
                return (Path *) create_memoize_path(root, rel,
                                                    spath,
                                                    mpath->param_exprs,
                                                    mpath->hash_operators,
                                                    mpath->singlerow,
                                                    mpath->binary_mode,
                                                    mpath->est_calls);
            }
        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.
 *
 * Most fields in the path are not changed, but any expressions must be
 * adjusted to refer to the correct varnos, and any subpaths 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.  So we need
 * not change those.
 *
 * 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 that this function can change referenced RangeTblEntries, RelOptInfos
 * and IndexOptInfos as well as the Path structures.  Therefore, it's only safe
 * to call during create_plan(), when we have made a final choice of which Path
 * to use for each RangeTblEntry/RelOptInfo/IndexOptInfo.
 *
 * Keep this code in sync with path_is_reparameterizable_by_child()!
 */
Path *
reparameterize_path_by_child(PlannerInfo *root, Path *path,
                             RelOptInfo *child_rel)
{
    Path       *new_path;
    ParamPathInfo *new_ppi;
    ParamPathInfo *old_ppi;
    Relids      required_outer;
 
#define ADJUST_CHILD_ATTRS(node) \
    ((node) = (void *) adjust_appendrel_attrs_multilevel(root, \
                                                         (Node *) (node), \
                                                         child_rel, \
                                                         child_rel->top_parent))
 
#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)
 
    /*
     * If the path is not parameterized by the 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.
     *
     * 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:
            new_path = path;
            ADJUST_CHILD_ATTRS(new_path->parent->baserestrictinfo);
            if (path->pathtype == T_SampleScan)
            {
                Index       scan_relid = path->parent->relid;
                RangeTblEntry *rte;
 
                /* it should be a base rel with a tablesample clause... */
                Assert(scan_relid > 0);
                rte = planner_rt_fetch(scan_relid, root);
                Assert(rte->rtekind == RTE_RELATION);
                Assert(rte->tablesample != NULL);
 
                ADJUST_CHILD_ATTRS(rte->tablesample);
            }
            break;
 
        case T_IndexPath:
            {
                IndexPath  *ipath = (IndexPath *) path;
 
                ADJUST_CHILD_ATTRS(ipath->indexinfo->indrestrictinfo);
                ADJUST_CHILD_ATTRS(ipath->indexclauses);
                new_path = (Path *) ipath;
            }
            break;
 
        case T_BitmapHeapPath:
            {
                BitmapHeapPath *bhpath = (BitmapHeapPath *) path;
 
                ADJUST_CHILD_ATTRS(bhpath->path.parent->baserestrictinfo);
                REPARAMETERIZE_CHILD_PATH(bhpath->bitmapqual);
                new_path = (Path *) bhpath;
            }
            break;
 
        case T_BitmapAndPath:
            {
                BitmapAndPath *bapath = (BitmapAndPath *) path;
 
                REPARAMETERIZE_CHILD_PATH_LIST(bapath->bitmapquals);
                new_path = (Path *) bapath;
            }
            break;
 
        case T_BitmapOrPath:
            {
                BitmapOrPath *bopath = (BitmapOrPath *) path;
 
                REPARAMETERIZE_CHILD_PATH_LIST(bopath->bitmapquals);
                new_path = (Path *) bopath;
            }
            break;
 
        case T_ForeignPath:
            {
                ForeignPath *fpath = (ForeignPath *) path;
                ReparameterizeForeignPathByChild_function rfpc_func;
 
                ADJUST_CHILD_ATTRS(fpath->path.parent->baserestrictinfo);
                if (fpath->fdw_outerpath)
                    REPARAMETERIZE_CHILD_PATH(fpath->fdw_outerpath);
                if (fpath->fdw_restrictinfo)
                    ADJUST_CHILD_ATTRS(fpath->fdw_restrictinfo);
 
                /* 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 = (CustomPath *) path;
 
                ADJUST_CHILD_ATTRS(cpath->path.parent->baserestrictinfo);
                REPARAMETERIZE_CHILD_PATH_LIST(cpath->custom_paths);
                if (cpath->custom_restrictinfo)
                    ADJUST_CHILD_ATTRS(cpath->custom_restrictinfo);
                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:
            {
                NestPath   *npath = (NestPath *) path;
                JoinPath   *jpath = (JoinPath *) npath;
 
                REPARAMETERIZE_CHILD_PATH(jpath->outerjoinpath);
                REPARAMETERIZE_CHILD_PATH(jpath->innerjoinpath);
                ADJUST_CHILD_ATTRS(jpath->joinrestrictinfo);
                new_path = (Path *) npath;
            }
            break;
 
        case T_MergePath:
            {
                MergePath  *mpath = (MergePath *) path;
                JoinPath   *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:
            {
                HashPath   *hpath = (HashPath *) path;
                JoinPath   *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 = (AppendPath *) path;
 
                REPARAMETERIZE_CHILD_PATH_LIST(apath->subpaths);
                new_path = (Path *) apath;
            }
            break;
 
        case T_MaterialPath:
            {
                MaterialPath *mpath = (MaterialPath *) path;
 
                REPARAMETERIZE_CHILD_PATH(mpath->subpath);
                new_path = (Path *) mpath;
            }
            break;
 
        case T_MemoizePath:
            {
                MemoizePath *mpath = (MemoizePath *) path;
 
                REPARAMETERIZE_CHILD_PATH(mpath->subpath);
                ADJUST_CHILD_ATTRS(mpath->param_exprs);
                new_path = (Path *) mpath;
            }
            break;
 
        case T_GatherPath:
            {
                GatherPath *gpath = (GatherPath *) path;
 
                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,
                                       child_rel->top_parent);
 
    /* 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);
        new_ppi->ppi_serials = bms_copy(old_ppi->ppi_serials);
        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;
}
 
/*
 * path_is_reparameterizable_by_child
 *      Given a path parameterized by the parent of the given child relation,
 *      see if it can be translated to be parameterized by the child relation.
 *
 * This must return true if and only if reparameterize_path_by_child()
 * would succeed on this path.  Currently it's sufficient to verify that
 * the path and all of its subpaths (if any) are of the types handled by
 * that function.  However, subpaths that are not parameterized can be
 * disregarded since they won't require translation.
 */
bool
path_is_reparameterizable_by_child(Path *path, RelOptInfo *child_rel)
{
#define REJECT_IF_PATH_NOT_REPARAMETERIZABLE(path) \
do { \
    if (!path_is_reparameterizable_by_child(path, child_rel)) \
        return false; \
} while(0)
 
#define REJECT_IF_PATH_LIST_NOT_REPARAMETERIZABLE(pathlist) \
do { \
    if (!pathlist_is_reparameterizable_by_child(pathlist, child_rel)) \
        return false; \
} while(0)
 
    /*
     * If the path is not parameterized by the 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 true;
 
    /*
     * Check that the path type is one that reparameterize_path_by_child() can
     * handle, and recursively check subpaths.
     */
    switch (nodeTag(path))
    {
        case T_Path:
        case T_IndexPath:
            break;
 
        case T_BitmapHeapPath:
            {
                BitmapHeapPath *bhpath = (BitmapHeapPath *) path;
 
                REJECT_IF_PATH_NOT_REPARAMETERIZABLE(bhpath->bitmapqual);
            }
            break;
 
        case T_BitmapAndPath:
            {
                BitmapAndPath *bapath = (BitmapAndPath *) path;
 
                REJECT_IF_PATH_LIST_NOT_REPARAMETERIZABLE(bapath->bitmapquals);
            }
            break;
 
        case T_BitmapOrPath:
            {
                BitmapOrPath *bopath = (BitmapOrPath *) path;
 
                REJECT_IF_PATH_LIST_NOT_REPARAMETERIZABLE(bopath->bitmapquals);
            }
            break;
 
        case T_ForeignPath:
            {
                ForeignPath *fpath = (ForeignPath *) path;
 
                if (fpath->fdw_outerpath)
                    REJECT_IF_PATH_NOT_REPARAMETERIZABLE(fpath->fdw_outerpath);
            }
            break;
 
        case T_CustomPath:
            {
                CustomPath *cpath = (CustomPath *) path;
 
                REJECT_IF_PATH_LIST_NOT_REPARAMETERIZABLE(cpath->custom_paths);
            }
            break;
 
        case T_NestPath:
        case T_MergePath:
        case T_HashPath:
            {
                JoinPath   *jpath = (JoinPath *) path;
 
                REJECT_IF_PATH_NOT_REPARAMETERIZABLE(jpath->outerjoinpath);
                REJECT_IF_PATH_NOT_REPARAMETERIZABLE(jpath->innerjoinpath);
            }
            break;
 
        case T_AppendPath:
            {
                AppendPath *apath = (AppendPath *) path;
 
                REJECT_IF_PATH_LIST_NOT_REPARAMETERIZABLE(apath->subpaths);
            }
            break;
 
        case T_MaterialPath:
            {
                MaterialPath *mpath = (MaterialPath *) path;
 
                REJECT_IF_PATH_NOT_REPARAMETERIZABLE(mpath->subpath);
            }
            break;
 
        case T_MemoizePath:
            {
                MemoizePath *mpath = (MemoizePath *) path;
 
                REJECT_IF_PATH_NOT_REPARAMETERIZABLE(mpath->subpath);
            }
            break;
 
        case T_GatherPath:
            {
                GatherPath *gpath = (GatherPath *) path;
 
                REJECT_IF_PATH_NOT_REPARAMETERIZABLE(gpath->subpath);
            }
            break;
 
        default:
            /* We don't know how to reparameterize this path. */
            return false;
    }
 
    return true;
}
 
/*
 * reparameterize_pathlist_by_child
 *      Helper function to reparameterize a list of paths by given child rel.
 *
 * Returns NIL to indicate failure, so pathlist had better not be NIL.
 */
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;
}
 
/*
 * pathlist_is_reparameterizable_by_child
 *      Helper function to check if a list of paths can be reparameterized.
 */
static bool
pathlist_is_reparameterizable_by_child(List *pathlist, RelOptInfo *child_rel)
{
    ListCell   *lc;
 
    foreach(lc, pathlist)
    {
        Path       *path = (Path *) lfirst(lc);
 
        if (!path_is_reparameterizable_by_child(path, child_rel))
            return false;
    }
 
    return true;
}