text: /*-------------------------------------------------------------------------
   *
   * 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
   *	  $PostgreSQL$
   *
   *-------------------------------------------------------------------------
   */
  #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;
  }
  