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Sourcecode: postgresql-8.4 version File versions

pathnode.c

/*-------------------------------------------------------------------------
 *
 * pathnode.c
 *      Routines to manipulate pathlists and create path nodes
 *
 * Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *      $PostgreSQL: pgsql/src/backend/optimizer/util/pathnode.c,v 1.152 2009/06/11 14:48:59 momjian Exp $
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include <math.h>

#include "catalog/pg_operator.h"
#include "executor/executor.h"
#include "miscadmin.h"
#include "optimizer/clauses.h"
#include "optimizer/cost.h"
#include "optimizer/pathnode.h"
#include "optimizer/paths.h"
#include "optimizer/tlist.h"
#include "optimizer/var.h"
#include "parser/parse_expr.h"
#include "parser/parsetree.h"
#include "utils/selfuncs.h"
#include "utils/lsyscache.h"
#include "utils/syscache.h"


static List *translate_sub_tlist(List *tlist, int relid);
static bool query_is_distinct_for(Query *query, List *colnos, List *opids);
static Oid  distinct_col_search(int colno, List *colnos, List *opids);


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

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

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

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

/*
 * compare_fuzzy_path_costs
 *      Return -1, 0, or +1 according as path1 is cheaper, the same cost,
 *      or more expensive than path2 for the specified criterion.
 *
 * This differs from compare_path_costs in that we consider the costs the
 * same if they agree to within a "fuzz factor".  This is used by add_path
 * to avoid keeping both of a pair of paths that really have insignificantly
 * different cost.
 */
static int
compare_fuzzy_path_costs(Path *path1, Path *path2, CostSelector criterion)
{
      /*
       * We use a fuzz factor of 1% of the smaller cost.
       *
       * XXX does this percentage need to be user-configurable?
       */
      if (criterion == STARTUP_COST)
      {
            if (path1->startup_cost > path2->startup_cost * 1.01)
                  return +1;
            if (path2->startup_cost > path1->startup_cost * 1.01)
                  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 * 1.01)
                  return +1;
            if (path2->total_cost > path1->total_cost * 1.01)
                  return -1;
      }
      else
      {
            if (path1->total_cost > path2->total_cost * 1.01)
                  return +1;
            if (path2->total_cost > path1->total_cost * 1.01)
                  return -1;

            /*
             * If paths have the same total cost, order them by startup cost.
             */
            if (path1->startup_cost > path2->startup_cost * 1.01)
                  return +1;
            if (path2->startup_cost > path1->startup_cost * 1.01)
                  return -1;
      }
      return 0;
}

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

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

/*
 * set_cheapest
 *      Find the minimum-cost paths from among a relation's paths,
 *      and save them in the rel's cheapest-path fields.
 *
 * This is normally called only after we've finished constructing the path
 * list for the rel node.
 *
 * 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 it.
 */
void
set_cheapest(RelOptInfo *parent_rel)
{
      List     *pathlist = parent_rel->pathlist;
      ListCell   *p;
      Path     *cheapest_startup_path;
      Path     *cheapest_total_path;

      Assert(IsA(parent_rel, RelOptInfo));

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

      cheapest_startup_path = cheapest_total_path = (Path *) linitial(pathlist);

      for_each_cell(p, lnext(list_head(pathlist)))
      {
            Path     *path = (Path *) lfirst(p);
            int               cmp;

            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;
      }

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

/*
 * 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 either a better sort order (better pathkeys)
 *      or cheaper cost (on either dimension) than any of the existing old paths.
 *
 *      We also remove from the rel's pathlist any old paths that are dominated
 *      by new_path --- that is, new_path is both cheaper and at least as well
 *      ordered.
 *
 *      The pathlist is kept sorted by TOTAL_COST metric, with cheaper paths
 *      at the front.  No code depends on that for correctness; it's simply
 *      a speed hack within this routine.  Doing it that way makes it more
 *      likely that we will reject an inferior path after a few comparisons,
 *      rather than many comparisons.
 *
 *      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.
 *
 *      BUT: we do not pfree IndexPath objects, since they may be referenced as
 *      children of BitmapHeapPaths as well as being paths in their own right.
 *
 * '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 */
      ListCell   *insert_after = NULL;    /* where to insert new item */
      ListCell   *p1_prev = NULL;
      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();

      /*
       * 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.
       */
      p1 = list_head(parent_rel->pathlist);           /* cannot use foreach here */
      while (p1 != NULL)
      {
            Path     *old_path = (Path *) lfirst(p1);
            bool        remove_old = false; /* unless new proves superior */
            int               costcmp;

            /*
             * As of Postgres 8.0, we use fuzzy cost comparison to avoid wasting
             * cycles keeping paths that are really not significantly different in
             * cost.
             */
            costcmp = compare_fuzzy_path_costs(new_path, old_path, TOTAL_COST);

            /*
             * If the two paths compare differently for startup and total cost,
             * then we want to keep both, and we can skip the (much slower)
             * comparison of pathkeys.    If they compare the same, proceed with the
             * pathkeys comparison.  Note: this test relies on the fact that
             * compare_fuzzy_path_costs will only return 0 if both costs are
             * effectively equal (and, therefore, there's no need to call it twice
             * in that case).
             */
            if (costcmp == 0 ||
                  costcmp == compare_fuzzy_path_costs(new_path, old_path,
                                                                        STARTUP_COST))
            {
                  switch (compare_pathkeys(new_path->pathkeys, old_path->pathkeys))
                  {
                        case PATHKEYS_EQUAL:
                              if (costcmp < 0)
                                    remove_old = true;            /* new dominates old */
                              else if (costcmp > 0)
                                    accept_new = false;           /* old dominates new */
                              else
                              {
                                    /*
                                     * Same pathkeys, and fuzzily the same cost, so keep
                                     * just one --- but we'll do an exact cost comparison
                                     * to decide which.
                                     */
                                    if (compare_path_costs(new_path, old_path,
                                                                     TOTAL_COST) < 0)
                                          remove_old = true;      /* new dominates old */
                                    else
                                          accept_new = false; /* old equals or dominates new */
                              }
                              break;
                        case PATHKEYS_BETTER1:
                              if (costcmp <= 0)
                                    remove_old = true;            /* new dominates old */
                              break;
                        case PATHKEYS_BETTER2:
                              if (costcmp >= 0)
                                    accept_new = false;           /* old dominates new */
                              break;
                        case PATHKEYS_DIFFERENT:
                              /* keep both paths, since they have different ordering */
                              break;
                  }
            }

            /*
             * Remove current element from pathlist if dominated by new.
             */
            if (remove_old)
            {
                  parent_rel->pathlist = list_delete_cell(parent_rel->pathlist,
                                                                              p1, p1_prev);

                  /*
                   * Delete the data pointed-to by the deleted cell, if possible
                   */
                  if (!IsA(old_path, IndexPath))
                        pfree(old_path);
                  /* Advance list pointer */
                  if (p1_prev)
                        p1 = lnext(p1_prev);
                  else
                        p1 = list_head(parent_rel->pathlist);
            }
            else
            {
                  /* new belongs after this old path if it has cost >= old's */
                  if (costcmp >= 0)
                        insert_after = p1;
                  /* Advance list pointers */
                  p1_prev = p1;
                  p1 = lnext(p1);
            }

            /*
             * 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 */
            if (insert_after)
                  lappend_cell(parent_rel->pathlist, insert_after, new_path);
            else
                  parent_rel->pathlist = lcons(new_path, parent_rel->pathlist);
      }
      else
      {
            /* Reject and recycle the new path */
            if (!IsA(new_path, IndexPath))
                  pfree(new_path);
      }
}


/*****************************************************************************
 *          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)
{
      Path     *pathnode = makeNode(Path);

      pathnode->pathtype = T_SeqScan;
      pathnode->parent = rel;
      pathnode->pathkeys = NIL;     /* seqscan has unordered result */

      cost_seqscan(pathnode, root, rel);

      return pathnode;
}

/*
 * create_index_path
 *      Creates a path node for an index scan.
 *
 * 'index' is a usable index.
 * 'clause_groups' is a list of lists of RestrictInfo nodes
 *                to be used as index qual conditions in the scan.
 * 'pathkeys' describes the ordering of the path.
 * 'indexscandir' is ForwardScanDirection or BackwardScanDirection
 *                for an ordered index, or NoMovementScanDirection for
 *                an unordered index.
 * 'outer_rel' is the outer relation if this is a join inner indexscan path.
 *                (pathkeys and indexscandir are ignored if so.)  NULL if not.
 *
 * Returns the new path node.
 */
IndexPath *
create_index_path(PlannerInfo *root,
                          IndexOptInfo *index,
                          List *clause_groups,
                          List *pathkeys,
                          ScanDirection indexscandir,
                          RelOptInfo *outer_rel)
{
      IndexPath  *pathnode = makeNode(IndexPath);
      RelOptInfo *rel = index->rel;
      List     *indexquals,
                     *allclauses;

      /*
       * For a join inner scan, there's no point in marking the path with any
       * pathkeys, since it will only ever be used as the inner path of a
       * nestloop, and so its ordering does not matter.  For the same reason we
       * don't really care what order it's scanned in.  (We could expect the
       * caller to supply the correct values, but it's easier to force it here.)
       */
      if (outer_rel != NULL)
      {
            pathkeys = NIL;
            indexscandir = NoMovementScanDirection;
      }

      pathnode->path.pathtype = T_IndexScan;
      pathnode->path.parent = rel;
      pathnode->path.pathkeys = pathkeys;

      /* Convert clauses to indexquals the executor can handle */
      indexquals = expand_indexqual_conditions(index, clause_groups);

      /* Flatten the clause-groups list to produce indexclauses list */
      allclauses = flatten_clausegroups_list(clause_groups);

      /* Fill in the pathnode */
      pathnode->indexinfo = index;
      pathnode->indexclauses = allclauses;
      pathnode->indexquals = indexquals;

      pathnode->isjoininner = (outer_rel != NULL);
      pathnode->indexscandir = indexscandir;

      if (outer_rel != NULL)
      {
            /*
             * We must compute the estimated number of output rows for the
             * indexscan.  This is less than rel->rows because of the additional
             * selectivity of the join clauses.  Since clause_groups may contain
             * both restriction and join clauses, we have to do a set union to get
             * the full set of clauses that must be considered to compute the
             * correct selectivity.  (Without the union operation, we might have
             * some restriction clauses appearing twice, which'd mislead
             * clauselist_selectivity into double-counting their selectivity.
             * However, since RestrictInfo nodes aren't copied when linking them
             * into different lists, it should be sufficient to use pointer
             * comparison to remove duplicates.)
             *
             * Note that we force the clauses to be treated as non-join clauses
             * during selectivity estimation.
             */
            allclauses = list_union_ptr(rel->baserestrictinfo, allclauses);
            pathnode->rows = rel->tuples *
                  clauselist_selectivity(root,
                                                   allclauses,
                                                   rel->relid,    /* do not use 0! */
                                                   JOIN_INNER,
                                                   NULL);
            /* Like costsize.c, force estimate to be at least one row */
            pathnode->rows = clamp_row_est(pathnode->rows);
      }
      else
      {
            /*
             * The number of rows is the same as the parent rel's estimate, since
             * this isn't a join inner indexscan.
             */
            pathnode->rows = rel->rows;
      }

      cost_index(pathnode, root, index, indexquals, outer_rel);

      return pathnode;
}

/*
 * create_bitmap_heap_path
 *      Creates a path node for a bitmap scan.
 *
 * 'bitmapqual' is a tree of IndexPath, BitmapAndPath, and BitmapOrPath nodes.
 *
 * If this is a join inner indexscan path, 'outer_rel' is the outer relation,
 * and all the component IndexPaths should have been costed accordingly.
 */
BitmapHeapPath *
create_bitmap_heap_path(PlannerInfo *root,
                                    RelOptInfo *rel,
                                    Path *bitmapqual,
                                    RelOptInfo *outer_rel)
{
      BitmapHeapPath *pathnode = makeNode(BitmapHeapPath);

      pathnode->path.pathtype = T_BitmapHeapScan;
      pathnode->path.parent = rel;
      pathnode->path.pathkeys = NIL;            /* always unordered */

      pathnode->bitmapqual = bitmapqual;
      pathnode->isjoininner = (outer_rel != NULL);

      if (pathnode->isjoininner)
      {
            /*
             * We must compute the estimated number of output rows for the
             * indexscan.  This is less than rel->rows because of the additional
             * selectivity of the join clauses.  We make use of the selectivity
             * estimated for the bitmap to do this; this isn't really quite right
             * since there may be restriction conditions not included in the
             * bitmap ...
             */
            Cost        indexTotalCost;
            Selectivity indexSelectivity;

            cost_bitmap_tree_node(bitmapqual, &indexTotalCost, &indexSelectivity);
            pathnode->rows = rel->tuples * indexSelectivity;
            if (pathnode->rows > rel->rows)
                  pathnode->rows = rel->rows;
            /* Like costsize.c, force estimate to be at least one row */
            pathnode->rows = clamp_row_est(pathnode->rows);
      }
      else
      {
            /*
             * The number of rows is the same as the parent rel's estimate, since
             * this isn't a join inner indexscan.
             */
            pathnode->rows = rel->rows;
      }

      cost_bitmap_heap_scan(&pathnode->path, root, rel, bitmapqual, outer_rel);

      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);

      pathnode->path.pathtype = T_BitmapAnd;
      pathnode->path.parent = rel;
      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);

      pathnode->path.pathtype = T_BitmapOr;
      pathnode->path.parent = rel;
      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)
{
      TidPath    *pathnode = makeNode(TidPath);

      pathnode->path.pathtype = T_TidScan;
      pathnode->path.parent = rel;
      pathnode->path.pathkeys = NIL;

      pathnode->tidquals = tidquals;

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

      return pathnode;
}

/*
 * create_append_path
 *      Creates a path corresponding to an Append plan, returning the
 *      pathnode.
 */
AppendPath *
create_append_path(RelOptInfo *rel, List *subpaths)
{
      AppendPath *pathnode = makeNode(AppendPath);
      ListCell   *l;

      pathnode->path.pathtype = T_Append;
      pathnode->path.parent = rel;
      pathnode->path.pathkeys = NIL;            /* result is always considered
                                                             * unsorted */
      pathnode->subpaths = subpaths;

      pathnode->path.startup_cost = 0;
      pathnode->path.total_cost = 0;
      foreach(l, subpaths)
      {
            Path     *subpath = (Path *) lfirst(l);

            if (l == list_head(subpaths)) /* first node? */
                  pathnode->path.startup_cost = subpath->startup_cost;
            pathnode->path.total_cost += subpath->total_cost;
      }

      return pathnode;
}

/*
 * create_result_path
 *      Creates a path representing a Result-and-nothing-else plan.
 *      This is only used for the case of a query with an empty jointree.
 */
ResultPath *
create_result_path(List *quals)
{
      ResultPath *pathnode = makeNode(ResultPath);

      pathnode->path.pathtype = T_Result;
      pathnode->path.parent = NULL;
      pathnode->path.pathkeys = NIL;
      pathnode->quals = quals;

      /* Ideally should define cost_result(), but I'm too lazy */
      pathnode->path.startup_cost = 0;
      pathnode->path.total_cost = cpu_tuple_cost;

      /*
       * In theory we should include the qual eval cost as well, but at present
       * that doesn't accomplish much except duplicate work that will be done
       * again in make_result; since this is only used for degenerate cases,
       * nothing interesting will be done with the path cost values...
       */

      return pathnode;
}

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

      pathnode->path.pathtype = T_Material;
      pathnode->path.parent = rel;

      pathnode->path.pathkeys = subpath->pathkeys;

      pathnode->subpath = subpath;

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

      return pathnode;
}

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

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

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

      /* If we previously failed, return NULL quickly */
      if (sjinfo->join_quals == NIL)
            return NULL;

      /*
       * We must ensure path struct and subsidiary data are allocated in main
       * planning context; otherwise GEQO memory management causes trouble.
       * (Compare best_inner_indexscan().)
       */
      oldcontext = MemoryContextSwitchTo(root->planner_cxt);

      /*----------
       * Look to see whether the semijoin's join quals consist of AND'ed
       * equality operators, with (only) RHS variables on only one side of
       * each one.  If so, we can figure out how to enforce uniqueness for
       * the RHS.
       *
       * Note that the input join_quals list is the list of quals that are
       * *syntactically* associated with the semijoin, which in practice means
       * the synthesized comparison list for an IN or the WHERE of an EXISTS.
       * Particularly in the latter case, it might contain clauses that aren't
       * *semantically* associated with the join, but refer to just one side or
       * the other.  We can ignore such clauses here, as they will just drop
       * down to be processed within one side or the other.  (It is okay to
       * consider only the syntactically-associated clauses here because for a
       * semijoin, no higher-level quals could refer to the RHS, and so there
       * can be no other quals that are semantically associated with this join.
       * We do things this way because it is useful to be able to run this test
       * before we have extracted the list of quals that are actually
       * semantically associated with the particular join.)
       *
       * Note that the in_operators list consists of the joinqual operators
       * themselves (but commuted if needed to put the RHS value on the right).
       * These could be cross-type operators, in which case the operator
       * actually needed for uniqueness is a related single-type operator.
       * We assume here that that operator will be available from the btree
       * or hash opclass when the time comes ... if not, create_unique_plan()
       * will fail.
       *----------
       */
      in_operators = NIL;
      uniq_exprs = NIL;
      all_btree = true;
      all_hash = enable_hashagg;    /* don't consider hash if not enabled */
      foreach(lc, sjinfo->join_quals)
      {
            OpExpr         *op = (OpExpr *) lfirst(lc);
            Oid               opno;
            Node     *left_expr;
            Node     *right_expr;
            Relids            left_varnos;
            Relids            right_varnos;
            Relids            all_varnos;

            /* Is it a binary opclause? */
            if (!IsA(op, OpExpr) ||
                  list_length(op->args) != 2)
            {
                  /* No, but does it reference both sides? */
                  all_varnos = pull_varnos((Node *) op);
                  if (!bms_overlap(all_varnos, sjinfo->syn_righthand) ||
                        bms_is_subset(all_varnos, sjinfo->syn_righthand))
                  {
                        /*
                         * Clause refers to only one rel, so ignore it --- unless it
                         * contains volatile functions, in which case we'd better
                         * punt.
                         */
                        if (contain_volatile_functions((Node *) op))
                              goto no_unique_path;
                        continue;
                  }
                  /* Non-operator clause referencing both sides, must punt */
                  goto no_unique_path;
            }

            /* Extract data from binary opclause */
            opno = op->opno;
            left_expr = linitial(op->args);
            right_expr = lsecond(op->args);
            left_varnos = pull_varnos(left_expr);
            right_varnos = pull_varnos(right_expr);
            all_varnos = bms_union(left_varnos, right_varnos);

            /* Does it reference both sides? */
            if (!bms_overlap(all_varnos, sjinfo->syn_righthand) ||
                  bms_is_subset(all_varnos, sjinfo->syn_righthand))
            {
                  /*
                   * Clause refers to only one rel, so ignore it --- unless it
                   * contains volatile functions, in which case we'd better punt.
                   */
                  if (contain_volatile_functions((Node *) op))
                        goto no_unique_path;
                  continue;
            }

            /* check rel membership of arguments */
            if (!bms_is_empty(right_varnos) &&
                  bms_is_subset(right_varnos, sjinfo->syn_righthand) &&
                  !bms_overlap(left_varnos, sjinfo->syn_righthand))
            {
                  /* typical case, right_expr is RHS variable */
            }
            else if (!bms_is_empty(left_varnos) &&
                         bms_is_subset(left_varnos, sjinfo->syn_righthand) &&
                         !bms_overlap(right_varnos, sjinfo->syn_righthand))
            {
                  /* flipped case, left_expr is RHS variable */
                  opno = get_commutator(opno);
                  if (!OidIsValid(opno))
                        goto no_unique_path;
                  right_expr = left_expr;
            }
            else
                  goto no_unique_path;

            /* all operators must be btree equality or hash equality */
            if (all_btree)
            {
                  /* oprcanmerge is considered a hint... */
                  if (!op_mergejoinable(opno) ||
                        get_mergejoin_opfamilies(opno) == NIL)
                        all_btree = false;
            }
            if (all_hash)
            {
                  /* ... but oprcanhash had better be correct */
                  if (!op_hashjoinable(opno))
                        all_hash = false;
            }
            if (!(all_btree || all_hash))
                  goto no_unique_path;

            /* so far so good, keep building lists */
            in_operators = lappend_oid(in_operators, opno);
            uniq_exprs = lappend(uniq_exprs, copyObject(right_expr));
      }

      /* Punt if we didn't find at least one column to unique-ify */
      if (uniq_exprs == NIL)
            goto no_unique_path;

      /*
       * The expressions we'd need to unique-ify mustn't be volatile.
       */
      if (contain_volatile_functions((Node *) uniq_exprs))
            goto no_unique_path;

      /*
       * If we get here, we can unique-ify using at least one of sorting and
       * hashing.  Start building the result Path object.
       */
      pathnode = makeNode(UniquePath);

      pathnode->path.pathtype = T_Unique;
      pathnode->path.parent = rel;

      /*
       * Treat the output as always unsorted, since we don't necessarily have
       * pathkeys to represent it.
       */
      pathnode->path.pathkeys = NIL;

      pathnode->subpath = subpath;
      pathnode->in_operators = in_operators;
      pathnode->uniq_exprs = uniq_exprs;

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

            sub_tlist_colnos = translate_sub_tlist(uniq_exprs, rel->relid);

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

                  rel->cheapest_unique_path = (Path *) pathnode;

                  MemoryContextSwitchTo(oldcontext);

                  return pathnode;
            }
      }

      /* Estimate number of output rows */
      pathnode->rows = estimate_num_groups(root, uniq_exprs, rel->rows);
      numCols = list_length(uniq_exprs);

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

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

      if (all_hash)
      {
            /*
             * Estimate the overhead per hashtable entry at 64 bytes (same as in
             * planner.c).
             */
            int               hashentrysize = rel->width + 64;

            if (hashentrysize * pathnode->rows > work_mem * 1024L)
                  all_hash = false; /* don't try to hash */
            else
                  cost_agg(&agg_path, root,
                               AGG_HASHED, 0,
                               numCols, pathnode->rows,
                               subpath->startup_cost,
                               subpath->total_cost,
                               rel->rows);
      }

      if (all_btree && all_hash)
      {
            if (agg_path.total_cost < sort_path.total_cost)
                  pathnode->umethod = UNIQUE_PATH_HASH;
            else
                  pathnode->umethod = UNIQUE_PATH_SORT;
      }
      else if (all_btree)
            pathnode->umethod = UNIQUE_PATH_SORT;
      else if (all_hash)
            pathnode->umethod = UNIQUE_PATH_HASH;
      else
            goto no_unique_path;

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

      rel->cheapest_unique_path = (Path *) pathnode;

      MemoryContextSwitchTo(oldcontext);

      return pathnode;

no_unique_path:               /* failure exit */

      /* Mark the SpecialJoinInfo as not unique-able */
      sjinfo->join_quals = NIL;

      MemoryContextSwitchTo(oldcontext);

      return NULL;
}

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

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

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

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

/*
 * query_is_distinct_for - does query never return duplicates of the
 *          specified columns?
 *
 * colnos is an integer list of output column numbers (resno's).  We are
 * interested in whether rows consisting of just these columns are certain
 * to be distinct.      "Distinctness" is defined according to whether the
 * corresponding upper-level equality operators listed in opids would think
 * the values are distinct.  (Note: the opids entries could be cross-type
 * operators, and thus not exactly the equality operators that the subquery
 * would use itself.  We use equality_ops_are_compatible() to check
 * compatibility.  That looks at btree or hash opfamily membership, and so
 * should give trustworthy answers for all operators that we might need
 * to deal with here.)
 */
static bool
query_is_distinct_for(Query *query, List *colnos, List *opids)
{
      ListCell   *l;
      Oid               opid;

      Assert(list_length(colnos) == list_length(opids));

      /*
       * DISTINCT (including DISTINCT ON) guarantees uniqueness if all the
       * columns in the DISTINCT clause appear in colnos and operator semantics
       * match.
       */
      if (query->distinctClause)
      {
            foreach(l, query->distinctClause)
            {
                  SortGroupClause *sgc = (SortGroupClause *) lfirst(l);
                  TargetEntry *tle = get_sortgroupclause_tle(sgc,
                                                                                 query->targetList);

                  opid = distinct_col_search(tle->resno, colnos, opids);
                  if (!OidIsValid(opid) ||
                        !equality_ops_are_compatible(opid, sgc->eqop))
                        break;                  /* exit early if no match */
            }
            if (l == NULL)                /* had matches for all? */
                  return true;
      }

      /*
       * Similarly, GROUP BY guarantees uniqueness if all the grouped columns
       * appear in colnos and operator semantics match.
       */
      if (query->groupClause)
      {
            foreach(l, query->groupClause)
            {
                  SortGroupClause *sgc = (SortGroupClause *) lfirst(l);
                  TargetEntry *tle = get_sortgroupclause_tle(sgc,
                                                                                 query->targetList);

                  opid = distinct_col_search(tle->resno, colnos, opids);
                  if (!OidIsValid(opid) ||
                        !equality_ops_are_compatible(opid, sgc->eqop))
                        break;                  /* exit early if no match */
            }
            if (l == NULL)                /* had matches for all? */
                  return true;
      }
      else
      {
            /*
             * If we have no GROUP BY, but do have aggregates or HAVING, then the
             * result is at most one row so it's surely unique, for any operators.
             */
            if (query->hasAggs || query->havingQual)
                  return true;
      }

      /*
       * UNION, INTERSECT, EXCEPT guarantee uniqueness of the whole output row,
       * except with ALL.
       */
      if (query->setOperations)
      {
            SetOperationStmt *topop = (SetOperationStmt *) query->setOperations;

            Assert(IsA(topop, SetOperationStmt));
            Assert(topop->op != SETOP_NONE);

            if (!topop->all)
            {
                  ListCell   *lg;

                  /* We're good if all the nonjunk output columns are in colnos */
                  lg = list_head(topop->groupClauses);
                  foreach(l, query->targetList)
                  {
                        TargetEntry *tle = (TargetEntry *) lfirst(l);
                        SortGroupClause *sgc;

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

                        /* non-resjunk columns should have grouping clauses */
                        Assert(lg != NULL);
                        sgc = (SortGroupClause *) lfirst(lg);
                        lg = lnext(lg);

                        opid = distinct_col_search(tle->resno, colnos, opids);
                        if (!OidIsValid(opid) ||
                              !equality_ops_are_compatible(opid, sgc->eqop))
                              break;            /* exit early if no match */
                  }
                  if (l == NULL)          /* had matches for all? */
                        return true;
            }
      }

      /*
       * XXX Are there any other cases in which we can easily see the result
       * must be distinct?
       */

      return false;
}

/*
 * distinct_col_search - subroutine for query_is_distinct_for
 *
 * If colno is in colnos, return the corresponding element of opids,
 * else return InvalidOid.    (We expect colnos does not contain duplicates,
 * so the result is well-defined.)
 */
static Oid
distinct_col_search(int colno, List *colnos, List *opids)
{
      ListCell   *lc1,
                     *lc2;

      forboth(lc1, colnos, lc2, opids)
      {
            if (colno == lfirst_int(lc1))
                  return lfirst_oid(lc2);
      }
      return InvalidOid;
}

/*
 * create_subqueryscan_path
 *      Creates a path corresponding to a sequential scan of a subquery,
 *      returning the pathnode.
 */
Path *
create_subqueryscan_path(RelOptInfo *rel, List *pathkeys)
{
      Path     *pathnode = makeNode(Path);

      pathnode->pathtype = T_SubqueryScan;
      pathnode->parent = rel;
      pathnode->pathkeys = pathkeys;

      cost_subqueryscan(pathnode, rel);

      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)
{
      Path     *pathnode = makeNode(Path);

      pathnode->pathtype = T_FunctionScan;
      pathnode->parent = rel;
      pathnode->pathkeys = NIL;     /* for now, assume unordered result */

      cost_functionscan(pathnode, root, rel);

      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)
{
      Path     *pathnode = makeNode(Path);

      pathnode->pathtype = T_ValuesScan;
      pathnode->parent = rel;
      pathnode->pathkeys = NIL;     /* result is always unordered */

      cost_valuesscan(pathnode, root, rel);

      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)
{
      Path     *pathnode = makeNode(Path);

      pathnode->pathtype = T_CteScan;
      pathnode->parent = rel;
      pathnode->pathkeys = NIL;     /* XXX for now, result is always unordered */

      cost_ctescan(pathnode, root, rel);

      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)
{
      Path     *pathnode = makeNode(Path);

      pathnode->pathtype = T_WorkTableScan;
      pathnode->parent = rel;
      pathnode->pathkeys = NIL;     /* result is always unordered */

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

      return pathnode;
}

/*
 * 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
 * 'sjinfo' is extra info about the join for selectivity estimation
 * '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
 *
 * Returns the resulting path node.
 */
NestPath *
create_nestloop_path(PlannerInfo *root,
                               RelOptInfo *joinrel,
                               JoinType jointype,
                               SpecialJoinInfo *sjinfo,
                               Path *outer_path,
                               Path *inner_path,
                               List *restrict_clauses,
                               List *pathkeys)
{
      NestPath   *pathnode = makeNode(NestPath);

      pathnode->path.pathtype = T_NestLoop;
      pathnode->path.parent = joinrel;
      pathnode->jointype = jointype;
      pathnode->outerjoinpath = outer_path;
      pathnode->innerjoinpath = inner_path;
      pathnode->joinrestrictinfo = restrict_clauses;
      pathnode->path.pathkeys = pathkeys;

      cost_nestloop(pathnode, root, sjinfo);

      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
 * 'sjinfo' is extra info about the join for selectivity estimation
 * '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
 * 'mergeclauses' are the RestrictInfo nodes to use as merge clauses
 *          (this should be a subset of the restrict_clauses list)
 * 'outersortkeys' are the sort varkeys for the outer relation
 * 'innersortkeys' are the sort varkeys for the inner relation
 */
MergePath *
create_mergejoin_path(PlannerInfo *root,
                                RelOptInfo *joinrel,
                                JoinType jointype,
                                SpecialJoinInfo *sjinfo,
                                Path *outer_path,
                                Path *inner_path,
                                List *restrict_clauses,
                                List *pathkeys,
                                List *mergeclauses,
                                List *outersortkeys,
                                List *innersortkeys)
{
      MergePath  *pathnode = makeNode(MergePath);

      /*
       * If the given paths are already well enough ordered, we can skip doing
       * an explicit sort.
       */
      if (outersortkeys &&
            pathkeys_contained_in(outersortkeys, outer_path->pathkeys))
            outersortkeys = NIL;
      if (innersortkeys &&
            pathkeys_contained_in(innersortkeys, inner_path->pathkeys))
            innersortkeys = NIL;

      /*
       * If we are not sorting the inner path, we may need a materialize node to
       * ensure it can be marked/restored.
       *
       * Since the inner side must be ordered, and only Sorts and IndexScans can
       * create order to begin with, and they both support mark/restore, you
       * might think there's no problem --- but you'd be wrong.  Nestloop and
       * merge joins can *preserve* the order of their inputs, so they can be
       * selected as the input of a mergejoin, and they don't support
       * mark/restore at present.
       *
       * Note: Sort supports mark/restore, so no materialize is really needed in
       * that case; but one may be desirable anyway to optimize the sort.
       * However, since we aren't representing the sort step separately in the
       * Path tree, we can't explicitly represent the materialize either. So
       * that case is not handled here.  Instead, cost_mergejoin has to factor
       * in the cost and create_mergejoin_plan has to add the plan node.
       */
      if (innersortkeys == NIL &&
            !ExecSupportsMarkRestore(inner_path->pathtype))
      {
            Path     *mpath;

            mpath = (Path *) create_material_path(inner_path->parent, inner_path);

            /*
             * We expect the materialize won't spill to disk (it could only do so
             * if there were a whole lot of duplicate tuples, which is a case
             * cost_mergejoin will avoid choosing anyway).  Therefore
             * cost_material's cost estimate is bogus and we should charge just
             * cpu_tuple_cost per tuple.  (Keep this estimate in sync with similar
             * ones in cost_mergejoin and create_mergejoin_plan.)
             */
            mpath->startup_cost = inner_path->startup_cost;
            mpath->total_cost = inner_path->total_cost;
            mpath->total_cost += cpu_tuple_cost * inner_path->parent->rows;

            inner_path = mpath;
      }

      pathnode->jpath.path.pathtype = T_MergeJoin;
      pathnode->jpath.path.parent = joinrel;
      pathnode->jpath.jointype = jointype;
      pathnode->jpath.outerjoinpath = outer_path;
      pathnode->jpath.innerjoinpath = inner_path;
      pathnode->jpath.joinrestrictinfo = restrict_clauses;
      pathnode->jpath.path.pathkeys = pathkeys;
      pathnode->path_mergeclauses = mergeclauses;
      pathnode->outersortkeys = outersortkeys;
      pathnode->innersortkeys = innersortkeys;

      cost_mergejoin(pathnode, root, sjinfo);

      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
 * 'sjinfo' is extra info about the join for selectivity estimation
 * 'outer_path' is the cheapest outer path
 * 'inner_path' is the cheapest inner path
 * 'restrict_clauses' are the RestrictInfo nodes to apply at the join
 * '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,
                               SpecialJoinInfo *sjinfo,
                               Path *outer_path,
                               Path *inner_path,
                               List *restrict_clauses,
                               List *hashclauses)
{
      HashPath   *pathnode = makeNode(HashPath);

      pathnode->jpath.path.pathtype = T_HashJoin;
      pathnode->jpath.path.parent = joinrel;
      pathnode->jpath.jointype = jointype;
      pathnode->jpath.outerjoinpath = outer_path;
      pathnode->jpath.innerjoinpath = inner_path;
      pathnode->jpath.joinrestrictinfo = restrict_clauses;

      /*
       * 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->path_hashclauses = hashclauses;
      /* cost_hashjoin will fill in pathnode->num_batches */

      cost_hashjoin(pathnode, root, sjinfo);

      return pathnode;
}

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