allpaths.c

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/*-------------------------------------------------------------------------
 *
 * allpaths.c
 *    Routines to find possible search paths for processing a query
 *
 * Portions Copyright (c) 1996-2013, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/optimizer/path/allpaths.c
 *
 *-------------------------------------------------------------------------
 */

#include "postgres.h"

#include <math.h>

#include "catalog/pg_class.h"
#include "foreign/fdwapi.h"
#include "nodes/nodeFuncs.h"
#ifdef OPTIMIZER_DEBUG
#include "nodes/print.h"
#endif
#include "optimizer/clauses.h"
#include "optimizer/cost.h"
#include "optimizer/geqo.h"
#include "optimizer/pathnode.h"
#include "optimizer/paths.h"
#include "optimizer/plancat.h"
#include "optimizer/planner.h"
#include "optimizer/prep.h"
#include "optimizer/restrictinfo.h"
#include "optimizer/var.h"
#include "parser/parse_clause.h"
#include "parser/parsetree.h"
#include "rewrite/rewriteManip.h"
#include "utils/lsyscache.h"


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

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


static void set_base_rel_sizes(PlannerInfo *root);
static void set_base_rel_pathlists(PlannerInfo *root);
static void set_rel_size(PlannerInfo *root, RelOptInfo *rel,
             Index rti, RangeTblEntry *rte);
static void set_rel_pathlist(PlannerInfo *root, RelOptInfo *rel,
                 Index rti, RangeTblEntry *rte);
static void set_plain_rel_size(PlannerInfo *root, RelOptInfo *rel,
                   RangeTblEntry *rte);
static void set_plain_rel_pathlist(PlannerInfo *root, RelOptInfo *rel,
                       RangeTblEntry *rte);
static void set_foreign_size(PlannerInfo *root, RelOptInfo *rel,
                 RangeTblEntry *rte);
static void set_foreign_pathlist(PlannerInfo *root, RelOptInfo *rel,
                     RangeTblEntry *rte);
static void set_append_rel_size(PlannerInfo *root, RelOptInfo *rel,
                    Index rti, RangeTblEntry *rte);
static void set_append_rel_pathlist(PlannerInfo *root, RelOptInfo *rel,
                        Index rti, RangeTblEntry *rte);
static void generate_mergeappend_paths(PlannerInfo *root, RelOptInfo *rel,
                           List *live_childrels,
                           List *all_child_pathkeys);
static List *accumulate_append_subpath(List *subpaths, Path *path);
static void set_dummy_rel_pathlist(RelOptInfo *rel);
static void set_subquery_pathlist(PlannerInfo *root, RelOptInfo *rel,
                      Index rti, RangeTblEntry *rte);
static void set_function_pathlist(PlannerInfo *root, RelOptInfo *rel,
                      RangeTblEntry *rte);
static void set_values_pathlist(PlannerInfo *root, RelOptInfo *rel,
                    RangeTblEntry *rte);
static void set_cte_pathlist(PlannerInfo *root, RelOptInfo *rel,
                 RangeTblEntry *rte);
static void set_worktable_pathlist(PlannerInfo *root, RelOptInfo *rel,
                       RangeTblEntry *rte);
static RelOptInfo *make_rel_from_joinlist(PlannerInfo *root, List *joinlist);
static bool subquery_is_pushdown_safe(Query *subquery, Query *topquery,
                          bool *differentTypes);
static bool recurse_pushdown_safe(Node *setOp, Query *topquery,
                      bool *differentTypes);
static void compare_tlist_datatypes(List *tlist, List *colTypes,
                        bool *differentTypes);
static bool qual_is_pushdown_safe(Query *subquery, Index rti, Node *qual,
                      bool *differentTypes);
static void subquery_push_qual(Query *subquery,
                   RangeTblEntry *rte, Index rti, Node *qual);
static void recurse_push_qual(Node *setOp, Query *topquery,
                  RangeTblEntry *rte, Index rti, Node *qual);


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

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

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

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

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

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

    /*
     * Generate access paths for the base rels.
     */
    set_base_rel_sizes(root);
    set_base_rel_pathlists(root);

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

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

    return rel;
}

/*
 * set_base_rel_sizes
 *    Set the size estimates (rows and widths) for each base-relation entry.
 *
 * We do this in a separate pass over the base rels so that rowcount
 * estimates are available for parameterized path generation.
 */
static void
set_base_rel_sizes(PlannerInfo *root)
{
    Index       rti;

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

    /*
     * Check to see if we can extract any restriction conditions from join
     * quals that are OR-of-AND structures.  If so, add them to the rel's
     * restriction list, and redo the above steps.
     */
    if (create_or_index_quals(root, rel))
    {
        check_partial_indexes(root, rel);
        set_baserel_size_estimates(root, rel);
    }
}

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

    /*
     * We don't support pushing join clauses into the quals of a seqscan, but
     * it could still have required parameterization due to LATERAL refs in
     * its tlist.  (That can only happen if the seqscan is on a relation
     * pulled up out of a UNION ALL appendrel.)
     */
    required_outer = rel->lateral_relids;

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

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

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

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

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

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

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

    /* Select cheapest path */
    set_cheapest(rel);
}

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

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

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

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

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

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

        /*
         * We have to copy the parent's targetlist and quals to the child,
         * with appropriate substitution of variables.  However, only the
         * baserestrictinfo quals are needed before we can check for
         * constraint exclusion; so do that first and then check to see if we
         * can disregard this child.
         *
         * As of 8.4, the child rel's targetlist might contain non-Var
         * expressions, which means that substitution into the quals could
         * produce opportunities for const-simplification, and perhaps even
         * pseudoconstant quals.  To deal with this, we strip the RestrictInfo
         * nodes, do the substitution, do const-simplification, and then
         * reconstitute the RestrictInfo layer.
         */
        childquals = get_all_actual_clauses(rel->baserestrictinfo);
        childquals = (List *) adjust_appendrel_attrs(root,
                                                     (Node *) childquals,
                                                     appinfo);
        childqual = eval_const_expressions(root, (Node *)
                                           make_ands_explicit(childquals));
        if (childqual && IsA(childqual, Const) &&
            (((Const *) childqual)->constisnull ||
             !DatumGetBool(((Const *) childqual)->constvalue)))
        {
            /*
             * Restriction reduces to constant FALSE or constant NULL after
             * substitution, so this child need not be scanned.
             */
            set_dummy_rel_pathlist(childrel);
            continue;
        }
        childquals = make_ands_implicit((Expr *) childqual);
        childquals = make_restrictinfos_from_actual_clauses(root,
                                                            childquals);
        childrel->baserestrictinfo = childquals;

        if (relation_excluded_by_constraints(root, childrel, childRTE))
        {
            /*
             * This child need not be scanned, so we can omit it from the
             * appendrel.
             */
            set_dummy_rel_pathlist(childrel);
            continue;
        }

        /*
         * CE failed, so finish copying/modifying targetlist and join quals.
         *
         * Note: the resulting childrel->reltargetlist may contain arbitrary
         * expressions, which otherwise would not occur in a reltargetlist.
         * Code that might be looking at an appendrel child must cope with
         * such.  Note in particular that "arbitrary expression" can include
         * "Var belonging to another relation", due to LATERAL references.
         */
        childrel->joininfo = (List *)
            adjust_appendrel_attrs(root,
                                   (Node *) rel->joininfo,
                                   appinfo);
        childrel->reltargetlist = (List *)
            adjust_appendrel_attrs(root,
                                   (Node *) rel->reltargetlist,
                                   appinfo);

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

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

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

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

        /*
         * Accumulate size information from each live child.
         */
        if (childrel->rows > 0)
        {
            parent_rows += childrel->rows;
            parent_size += childrel->width * childrel->rows;

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

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

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

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

    /*
     * Save the finished size estimates.
     */
    rel->rows = parent_rows;
    if (parent_rows > 0)
    {
        int         i;

        rel->width = rint(parent_size / parent_rows);
        for (i = 0; i < nattrs; i++)
            rel->attr_widths[i] = rint(parent_attrsizes[i] / parent_rows);
    }
    else
        rel->width = 0;         /* attr_widths should be zero already */

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

    pfree(parent_attrsizes);
}

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

    /*
     * Generate access paths for each member relation, and remember the
     * cheapest path for each one.  Also, identify all pathkeys (orderings)
     * and parameterizations (required_outer sets) available for the member
     * relations.
     */
    foreach(l, root->append_rel_list)
    {
        AppendRelInfo *appinfo = (AppendRelInfo *) lfirst(l);
        int         childRTindex;
        RangeTblEntry *childRTE;
        RelOptInfo *childrel;
        ListCell   *lcp;

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

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

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

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

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

        /*
         * If child has an unparameterized cheapest-total path, add that to
         * the unparameterized Append path we are constructing for the parent.
         * If not, there's no workable unparameterized path.
         */
        if (childrel->cheapest_total_path->param_info == NULL)
            subpaths = accumulate_append_subpath(subpaths,
                                             childrel->cheapest_total_path);
        else
            subpaths_valid = false;

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

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

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

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

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

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

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

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

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

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

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

            cheapest_total =
                get_cheapest_path_for_pathkeys(childrel->pathlist,
                                               NIL,
                                               required_outer,
                                               TOTAL_COST);
            Assert(cheapest_total != NULL);

            /* Children must have exactly the desired parameterization */
            if (!bms_equal(PATH_REQ_OUTER(cheapest_total), required_outer))
            {
                cheapest_total = reparameterize_path(root, cheapest_total,
                                                     required_outer, 1.0);
                if (cheapest_total == NULL)
                {
                    subpaths_valid = false;
                    break;
                }
            }

            subpaths = accumulate_append_subpath(subpaths, cheapest_total);
        }

        if (subpaths_valid)
            add_path(rel, (Path *)
                     create_append_path(rel, subpaths, required_outer));
    }

    /* Select cheapest paths */
    set_cheapest(rel);
}

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

    foreach(lcp, all_child_pathkeys)
    {
        List       *pathkeys = (List *) lfirst(lcp);
        List       *startup_subpaths = NIL;
        List       *total_subpaths = NIL;
        bool        startup_neq_total = false;
        ListCell   *lcr;

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

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

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

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

            startup_subpaths =
                accumulate_append_subpath(startup_subpaths, cheapest_startup);
            total_subpaths =
                accumulate_append_subpath(total_subpaths, cheapest_total);
        }

        /* ... and build the MergeAppend paths */
        add_path(rel, (Path *) create_merge_append_path(root,
                                                        rel,
                                                        startup_subpaths,
                                                        pathkeys,
                                                        NULL));
        if (startup_neq_total)
            add_path(rel, (Path *) create_merge_append_path(root,
                                                            rel,
                                                            total_subpaths,
                                                            pathkeys,
                                                            NULL));
    }
}

/*
 * accumulate_append_subpath
 *      Add a subpath to the list being built for an Append or MergeAppend
 *
 * It's possible that the child is itself an Append path, in which case
 * we can "cut out the middleman" and just add its child paths to our
 * own list.  (We don't try to do this earlier because we need to
 * apply both levels of transformation to the quals.)
 */
static List *
accumulate_append_subpath(List *subpaths, Path *path)
{
    if (IsA(path, AppendPath))
    {
        AppendPath *apath = (AppendPath *) path;

        /* list_copy is important here to avoid sharing list substructure */
        return list_concat(subpaths, list_copy(apath->subpaths));
    }
    else
        return lappend(subpaths, path);
}

/*
 * set_dummy_rel_pathlist
 *    Build a dummy path for a relation that's been excluded by constraints
 *
 * Rather than inventing a special "dummy" path type, we represent this as an
 * AppendPath with no members (see also IS_DUMMY_PATH/IS_DUMMY_REL macros).
 */
static void
set_dummy_rel_pathlist(RelOptInfo *rel)
{
    /* Set dummy size estimates --- we leave attr_widths[] as zeroes */
    rel->rows = 0;
    rel->width = 0;

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

    add_path(rel, (Path *) create_append_path(rel, NIL, NULL));

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

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

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

        if (brel == NULL)
            continue;

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

/*
 * set_subquery_pathlist
 *      Build the (single) access path for a subquery RTE
 *
 * We don't currently support generating parameterized paths for subqueries
 * by pushing join clauses down into them; it seems too expensive to re-plan
 * the subquery multiple times to consider different alternatives.  So the
 * subquery will have exactly one path.  (The path will be parameterized
 * if the subquery contains LATERAL references, otherwise not.)  Since there's
 * no freedom of action here, there's no need for a separate set_subquery_size
 * phase: we just make the path right away.
 */
static void
set_subquery_pathlist(PlannerInfo *root, RelOptInfo *rel,
                      Index rti, RangeTblEntry *rte)
{
    Query      *parse = root->parse;
    Query      *subquery = rte->subquery;
    Relids      required_outer;
    bool       *differentTypes;
    double      tuple_fraction;
    PlannerInfo *subroot;
    List       *pathkeys;

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

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

    /* We need a workspace for keeping track of set-op type coercions */
    differentTypes = (bool *)
        palloc0((list_length(subquery->targetList) + 1) * sizeof(bool));

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

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

            if (!rinfo->pseudoconstant &&
                (!rte->security_barrier ||
                 !contain_leaky_functions(clause)) &&
                qual_is_pushdown_safe(subquery, rti, clause, differentTypes))
            {
                /* Push it down */
                subquery_push_qual(subquery, rte, rti, clause);
            }
            else
            {
                /* Keep it in the upper query */
                upperrestrictlist = lappend(upperrestrictlist, rinfo);
            }
        }
        rel->baserestrictinfo = upperrestrictlist;
    }

    pfree(differentTypes);

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

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

    /* Generate the plan for the subquery */
    rel->subplan = subquery_planner(root->glob, subquery,
                                    root,
                                    false, tuple_fraction,
                                    &subroot);
    rel->subroot = subroot;

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

    /*
     * It's possible that constraint exclusion proved the subquery empty. If
     * so, it's convenient to turn it back into a dummy path so that we will
     * recognize appropriate optimizations at this query level.  (But see
     * create_append_plan in createplan.c, which has to reverse this
     * substitution.)
     */
    if (is_dummy_plan(rel->subplan))
    {
        set_dummy_rel_pathlist(rel);
        return;
    }

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

    /* Convert subquery pathkeys to outer representation */
    pathkeys = convert_subquery_pathkeys(root, rel, subroot->query_pathkeys);

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

    /*
     * We don't support pushing join clauses into the quals of a CTE scan, but
     * it could still have required parameterization due to LATERAL refs in
     * its tlist.  (That can only happen if the CTE scan is on a relation
     * pulled up out of a UNION ALL appendrel.)
     */
    required_outer = rel->lateral_relids;

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

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

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

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

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

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

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

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

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

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

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

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

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

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

        initial_rels = lappend(initial_rels, thisrel);
    }

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

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

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

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

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

    root->join_rel_level[1] = initial_rels;

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

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

        /*
         * Do cleanup work on each just-processed rel.
         */
        foreach(lc, root->join_rel_level[lev])
        {
            rel = (RelOptInfo *) lfirst(lc);

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

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

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

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

    root->join_rel_level = NULL;

    return rel;
}

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

/*
 * subquery_is_pushdown_safe - is a subquery safe for pushing down quals?
 *
 * subquery is the particular component query being checked.  topquery
 * is the top component of a set-operations tree (the same Query if no
 * set-op is involved).
 *
 * Conditions checked here:
 *
 * 1. If the subquery has a LIMIT clause, we must not push down any quals,
 * since that could change the set of rows returned.
 *
 * 2. If the subquery contains any window functions, we can't push quals
 * into it, because that could change the results.
 *
 * 3. If the subquery contains EXCEPT or EXCEPT ALL set ops we cannot push
 * quals into it, because that could change the results.
 *
 * 4. For subqueries using UNION/UNION ALL/INTERSECT/INTERSECT ALL, we can
 * push quals into each component query, but the quals can only reference
 * subquery columns that suffer no type coercions in the set operation.
 * Otherwise there are possible semantic gotchas.  So, we check the
 * component queries to see if any of them have different output types;
 * differentTypes[k] is set true if column k has different type in any
 * component.
 */
static bool
subquery_is_pushdown_safe(Query *subquery, Query *topquery,
                          bool *differentTypes)
{
    SetOperationStmt *topop;

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

    /* Check point 2 */
    if (subquery->hasWindowFuncs)
        return false;

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

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

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

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

/*
 * Compare tlist's datatypes against the list of set-operation result types.
 * For any items that are different, mark the appropriate element of
 * differentTypes[] to show that this column will have type conversions.
 *
 * We don't have to care about typmods here: the only allowed difference
 * between set-op input and output typmods is input is a specific typmod
 * and output is -1, and that does not require a coercion.
 */
static void
compare_tlist_datatypes(List *tlist, List *colTypes,
                        bool *differentTypes)
{
    ListCell   *l;
    ListCell   *colType = list_head(colTypes);

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

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

/*
 * qual_is_pushdown_safe - is a particular qual safe to push down?
 *
 * qual is a restriction clause applying to the given subquery (whose RTE
 * has index rti in the parent query).
 *
 * Conditions checked here:
 *
 * 1. The qual must not contain any subselects (mainly because I'm not sure
 * it will work correctly: sublinks will already have been transformed into
 * subplans in the qual, but not in the subquery).
 *
 * 2. The qual must not refer to the whole-row output of the subquery
 * (since there is no easy way to name that within the subquery itself).
 *
 * 3. The qual must not refer to any subquery output columns that were
 * found to have inconsistent types across a set operation tree by
 * subquery_is_pushdown_safe().
 *
 * 4. If the subquery uses DISTINCT ON, we must not push down any quals that
 * refer to non-DISTINCT output columns, because that could change the set
 * of rows returned.  (This condition is vacuous for DISTINCT, because then
 * there are no non-DISTINCT output columns, so we needn't check.  But note
 * we are assuming that the qual can't distinguish values that the DISTINCT
 * operator sees as equal.  This is a bit shaky but we have no way to test
 * for the case, and it's unlikely enough that we shouldn't refuse the
 * optimization just because it could theoretically happen.)
 *
 * 5. We must not push down any quals that refer to subselect outputs that
 * return sets, else we'd introduce functions-returning-sets into the
 * subquery's WHERE/HAVING quals.
 *
 * 6. We must not push down any quals that refer to subselect outputs that
 * contain volatile functions, for fear of introducing strange results due
 * to multiple evaluation of a volatile function.
 */
static bool
qual_is_pushdown_safe(Query *subquery, Index rti, Node *qual,
                      bool *differentTypes)
{
    bool        safe = true;
    List       *vars;
    ListCell   *vl;
    Bitmapset  *tested = NULL;

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

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

    /*
     * Examine all Vars used in clause; since it's a restriction clause, all
     * such Vars must refer to subselect output columns.
     */
    vars = pull_var_clause(qual,
                           PVC_REJECT_AGGREGATES,
                           PVC_INCLUDE_PLACEHOLDERS);
    foreach(vl, vars)
    {
        Var        *var = (Var *) lfirst(vl);
        TargetEntry *tle;

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

        Assert(var->varno == rti);

        /* Check point 2 */
        if (var->varattno == 0)
        {
            safe = false;
            break;
        }

        /*
         * We use a bitmapset to avoid testing the same attno more than once.
         * (NB: this only works because subquery outputs can't have negative
         * attnos.)
         */
        if (bms_is_member(var->varattno, tested))
            continue;
        tested = bms_add_member(tested, var->varattno);

        /* Check point 3 */
        if (differentTypes[var->varattno])
        {
            safe = false;
            break;
        }

        /* Must find the tlist element referenced by the Var */
        tle = get_tle_by_resno(subquery->targetList, var->varattno);
        Assert(tle != NULL);
        Assert(!tle->resjunk);

        /* If subquery uses DISTINCT ON, check point 4 */
        if (subquery->hasDistinctOn &&
            !targetIsInSortList(tle, InvalidOid, subquery->distinctClause))
        {
            /* non-DISTINCT column, so fail */
            safe = false;
            break;
        }

        /* Refuse functions returning sets (point 5) */
        if (expression_returns_set((Node *) tle->expr))
        {
            safe = false;
            break;
        }

        /* Refuse volatile functions (point 6) */
        if (contain_volatile_functions((Node *) tle->expr))
        {
            safe = false;
            break;
        }
    }

    list_free(vars);
    bms_free(tested);

    return safe;
}

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

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

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

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

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

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

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

#ifdef OPTIMIZER_DEBUG

static void
print_relids(Relids relids)
{
    Relids      tmprelids;
    int         x;
    bool        first = true;

    tmprelids = bms_copy(relids);
    while ((x = bms_first_member(tmprelids)) >= 0)
    {
        if (!first)
            printf(" ");
        printf("%d", x);
        first = false;
    }
    bms_free(tmprelids);
}

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

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

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

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

    switch (nodeTag(path))
    {
        case T_Path:
            ptype = "SeqScan";
            break;
        case T_IndexPath:
            ptype = "IdxScan";
            break;
        case T_BitmapHeapPath:
            ptype = "BitmapHeapScan";
            break;
        case T_BitmapAndPath:
            ptype = "BitmapAndPath";
            break;
        case T_BitmapOrPath:
            ptype = "BitmapOrPath";
            break;
        case T_TidPath:
            ptype = "TidScan";
            break;
        case T_ForeignPath:
            ptype = "ForeignScan";
            break;
        case T_AppendPath:
            ptype = "Append";
            break;
        case T_MergeAppendPath:
            ptype = "MergeAppend";
            break;
        case T_ResultPath:
            ptype = "Result";
            break;
        case T_MaterialPath:
            ptype = "Material";
            subpath = ((MaterialPath *) path)->subpath;
            break;
        case T_UniquePath:
            ptype = "Unique";
            subpath = ((UniquePath *) path)->subpath;
            break;
        case T_NestPath:
            ptype = "NestLoop";
            join = true;
            break;
        case T_MergePath:
            ptype = "MergeJoin";
            join = true;
            break;
        case T_HashPath:
            ptype = "HashJoin";
            join = true;
            break;
        default:
            ptype = "???Path";
            break;
    }

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

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

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

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

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

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

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

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

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

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

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

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

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

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

#endif   /* OPTIMIZER_DEBUG */