text: /*-------------------------------------------------------------------------
   *
   * indxpath.c
   *	  Routines to determine which indexes are usable for scanning a
   *	  given relation, and create Paths accordingly.
   *
   * Portions Copyright (c) 1996-2016, PostgreSQL Global Development Group
   * Portions Copyright (c) 1994, Regents of the University of California
   *
   *
   * IDENTIFICATION
   *	  src/backend/optimizer/path/indxpath.c
   *
   *-------------------------------------------------------------------------
   */
  #include "postgres.h"
  
  #include <math.h>
  
  #include "access/stratnum.h"
  #include "access/sysattr.h"
  #include "catalog/pg_am.h"
  #include "catalog/pg_collation.h"
  #include "catalog/pg_operator.h"
  #include "catalog/pg_opfamily.h"
  #include "catalog/pg_type.h"
  #include "nodes/makefuncs.h"
  #include "optimizer/clauses.h"
  #include "optimizer/cost.h"
  #include "optimizer/pathnode.h"
  #include "optimizer/paths.h"
  #include "optimizer/predtest.h"
  #include "optimizer/prep.h"
  #include "optimizer/restrictinfo.h"
  #include "optimizer/var.h"
  #include "utils/builtins.h"
  #include "utils/bytea.h"
  #include "utils/lsyscache.h"
  #include "utils/pg_locale.h"
  #include "utils/selfuncs.h"
  
  
  #define IsBooleanOpfamily(opfamily) \
  	((opfamily) == BOOL_BTREE_FAM_OID || (opfamily) == BOOL_HASH_FAM_OID)
  
  #define IndexCollMatchesExprColl(idxcollation, exprcollation) \
  	((idxcollation) == InvalidOid || (idxcollation) == (exprcollation))
  
  /* Whether we are looking for plain indexscan, bitmap scan, or either */
  typedef enum
  {
  	ST_INDEXSCAN,				/* must support amgettuple */
  	ST_BITMAPSCAN,				/* must support amgetbitmap */
  	ST_ANYSCAN					/* either is okay */
  } ScanTypeControl;
  
  /* Data structure for collecting qual clauses that match an index */
  typedef struct
  {
  	bool		nonempty;		/* True if lists are not all empty */
  	/* Lists of RestrictInfos, one per index column */
  	List	   *indexclauses[INDEX_MAX_KEYS];
  } IndexClauseSet;
  
  /* Per-path data used within choose_bitmap_and() */
  typedef struct
  {
  	Path	   *path;			/* IndexPath, BitmapAndPath, or BitmapOrPath */
  	List	   *quals;			/* the WHERE clauses it uses */
  	List	   *preds;			/* predicates of its partial index(es) */
  	Bitmapset  *clauseids;		/* quals+preds represented as a bitmapset */
  } PathClauseUsage;
  
  /* Callback argument for ec_member_matches_indexcol */
  typedef struct
  {
  	IndexOptInfo *index;		/* index we're considering */
  	int			indexcol;		/* index column we want to match to */
  } ec_member_matches_arg;
  
  
  static void consider_index_join_clauses(PlannerInfo *root, RelOptInfo *rel,
  							IndexOptInfo *index,
  							IndexClauseSet *rclauseset,
  							IndexClauseSet *jclauseset,
  							IndexClauseSet *eclauseset,
  							List **bitindexpaths);
  static void consider_index_join_outer_rels(PlannerInfo *root, RelOptInfo *rel,
  							   IndexOptInfo *index,
  							   IndexClauseSet *rclauseset,
  							   IndexClauseSet *jclauseset,
  							   IndexClauseSet *eclauseset,
  							   List **bitindexpaths,
  							   List *indexjoinclauses,
  							   int considered_clauses,
  							   List **considered_relids);
  static void get_join_index_paths(PlannerInfo *root, RelOptInfo *rel,
  					 IndexOptInfo *index,
  					 IndexClauseSet *rclauseset,
  					 IndexClauseSet *jclauseset,
  					 IndexClauseSet *eclauseset,
  					 List **bitindexpaths,
  					 Relids relids,
  					 List **considered_relids);
  static bool eclass_already_used(EquivalenceClass *parent_ec, Relids oldrelids,
  					List *indexjoinclauses);
  static bool bms_equal_any(Relids relids, List *relids_list);
  static void get_index_paths(PlannerInfo *root, RelOptInfo *rel,
  				IndexOptInfo *index, IndexClauseSet *clauses,
  				List **bitindexpaths);
  static List *build_index_paths(PlannerInfo *root, RelOptInfo *rel,
  				  IndexOptInfo *index, IndexClauseSet *clauses,
  				  bool useful_predicate,
  				  ScanTypeControl scantype,
  				  bool *skip_nonnative_saop,
  				  bool *skip_lower_saop);
  static List *build_paths_for_OR(PlannerInfo *root, RelOptInfo *rel,
  				   List *clauses, List *other_clauses);
  static List *generate_bitmap_or_paths(PlannerInfo *root, RelOptInfo *rel,
  						 List *clauses, List *other_clauses);
  static Path *choose_bitmap_and(PlannerInfo *root, RelOptInfo *rel,
  				  List *paths);
  static int	path_usage_comparator(const void *a, const void *b);
  static Cost bitmap_scan_cost_est(PlannerInfo *root, RelOptInfo *rel,
  					 Path *ipath);
  static Cost bitmap_and_cost_est(PlannerInfo *root, RelOptInfo *rel,
  					List *paths);
  static PathClauseUsage *classify_index_clause_usage(Path *path,
  							List **clauselist);
  static Relids get_bitmap_tree_required_outer(Path *bitmapqual);
  static void find_indexpath_quals(Path *bitmapqual, List **quals, List **preds);
  static int	find_list_position(Node *node, List **nodelist);
  static bool check_index_only(RelOptInfo *rel, IndexOptInfo *index,
  							 List *index_clauses, List *clause_columns);
  static double get_loop_count(PlannerInfo *root, Index cur_relid, Relids outer_relids);
  static double adjust_rowcount_for_semijoins(PlannerInfo *root,
  							  Index cur_relid,
  							  Index outer_relid,
  							  double rowcount);
  static double approximate_joinrel_size(PlannerInfo *root, Relids relids);
  static void match_restriction_clauses_to_index(RelOptInfo *rel,
  								   IndexOptInfo *index,
  								   IndexClauseSet *clauseset);
  static void match_join_clauses_to_index(PlannerInfo *root,
  							RelOptInfo *rel, IndexOptInfo *index,
  							IndexClauseSet *clauseset,
  							List **joinorclauses);
  static void match_eclass_clauses_to_index(PlannerInfo *root,
  							  IndexOptInfo *index,
  							  IndexClauseSet *clauseset);
  static void match_clauses_to_index(IndexOptInfo *index,
  					   List *clauses,
  					   IndexClauseSet *clauseset);
  static void match_clause_to_index(IndexOptInfo *index,
  					  RestrictInfo *rinfo,
  					  IndexClauseSet *clauseset);
  static bool match_clause_to_indexcol(IndexOptInfo *index,
  						 int indexcol,
  						 RestrictInfo *rinfo);
  static bool is_indexable_operator(Oid expr_op, Oid opfamily,
  					  bool indexkey_on_left);
  static bool match_rowcompare_to_indexcol(IndexOptInfo *index,
  							 int indexcol,
  							 Oid opfamily,
  							 Oid idxcollation,
  							 RowCompareExpr *clause);
  static void match_pathkeys_to_index(IndexOptInfo *index, List *pathkeys,
  						List **orderby_clauses_p,
  						List **clause_columns_p);
  static Expr *match_clause_to_ordering_op(IndexOptInfo *index,
  							int indexcol, Expr *clause, Oid pk_opfamily);
  static bool ec_member_matches_indexcol(PlannerInfo *root, RelOptInfo *rel,
  						   EquivalenceClass *ec, EquivalenceMember *em,
  						   void *arg);
  static bool match_boolean_index_clause(Node *clause, int indexcol,
  						   IndexOptInfo *index);
  static bool match_special_index_operator(Expr *clause,
  							 Oid opfamily, Oid idxcollation,
  							 bool indexkey_on_left);
  static Expr *expand_boolean_index_clause(Node *clause, int indexcol,
  							IndexOptInfo *index);
  static List *expand_indexqual_opclause(RestrictInfo *rinfo,
  						  Oid opfamily, Oid idxcollation);
  static RestrictInfo *expand_indexqual_rowcompare(RestrictInfo *rinfo,
  							IndexOptInfo *index,
  							int indexcol);
  static List *prefix_quals(Node *leftop, Oid opfamily, Oid collation,
  			 Const *prefix, Pattern_Prefix_Status pstatus);
  static List *network_prefix_quals(Node *leftop, Oid expr_op, Oid opfamily,
  					 Datum rightop);
  static Datum string_to_datum(const char *str, Oid datatype);
  static Const *string_to_const(const char *str, Oid datatype);
  
  
  /*
   * create_index_paths()
   *	  Generate all interesting index paths for the given relation.
   *	  Candidate paths are added to the rel's pathlist (using add_path).
   *
   * To be considered for an index scan, an index must match one or more
   * restriction clauses or join clauses from the query's qual condition,
   * or match the query's ORDER BY condition, or have a predicate that
   * matches the query's qual condition.
   *
   * There are two basic kinds of index scans.  A "plain" index scan uses
   * only restriction clauses (possibly none at all) in its indexqual,
   * so it can be applied in any context.  A "parameterized" index scan uses
   * join clauses (plus restriction clauses, if available) in its indexqual.
   * When joining such a scan to one of the relations supplying the other
   * variables used in its indexqual, the parameterized scan must appear as
   * the inner relation of a nestloop join; it can't be used on the outer side,
   * nor in a merge or hash join.  In that context, values for the other rels'
   * attributes are available and fixed during any one scan of the indexpath.
   *
   * An IndexPath is generated and submitted to add_path() for each plain or
   * parameterized index scan this routine deems potentially interesting for
   * the current query.
   *
   * 'rel' is the relation for which we want to generate index paths
   *
   * Note: check_index_predicates() must have been run previously for this rel.
   *
   * Note: in cases involving LATERAL references in the relation's tlist, it's
   * possible that rel->lateral_relids is nonempty.  Currently, we include
   * lateral_relids into the parameterization reported for each path, but don't
   * take it into account otherwise.  The fact that any such rels *must* be
   * available as parameter sources perhaps should influence our choices of
   * index quals ... but for now, it doesn't seem worth troubling over.
   * In particular, comments below about "unparameterized" paths should be read
   * as meaning "unparameterized so far as the indexquals are concerned".
   */
  void
  create_index_paths(PlannerInfo *root, RelOptInfo *rel)
  {
  	List	   *indexpaths;
  	List	   *bitindexpaths;
  	List	   *bitjoinpaths;
  	List	   *joinorclauses;
  	IndexClauseSet rclauseset;
  	IndexClauseSet jclauseset;
  	IndexClauseSet eclauseset;
  	ListCell   *lc;
  
  	/* Skip the whole mess if no indexes */
  	if (rel->indexlist == NIL)
  		return;
  
  	/* Bitmap paths are collected and then dealt with at the end */
  	bitindexpaths = bitjoinpaths = joinorclauses = NIL;
  
  	/* Examine each index in turn */
  	foreach(lc, rel->indexlist)
  	{
  		IndexOptInfo *index = (IndexOptInfo *) lfirst(lc);
  
  		/* Protect limited-size array in IndexClauseSets */
  		Assert(index->ncolumns <= INDEX_MAX_KEYS);
  
  		/*
  		 * Ignore partial indexes that do not match the query.
  		 * (generate_bitmap_or_paths() might be able to do something with
  		 * them, but that's of no concern here.)
  		 */
  		if (index->indpred != NIL && !index->predOK)
  			continue;
  
  		/*
  		 * Identify the restriction clauses that can match the index.
  		 */
  		MemSet(&rclauseset, 0, sizeof(rclauseset));
  		match_restriction_clauses_to_index(rel, index, &rclauseset);
  
  		/*
  		 * Build index paths from the restriction clauses.  These will be
  		 * non-parameterized paths.  Plain paths go directly to add_path(),
  		 * bitmap paths are added to bitindexpaths to be handled below.
  		 */
  		get_index_paths(root, rel, index, &rclauseset,
  						&bitindexpaths);
  
  		/*
  		 * Identify the join clauses that can match the index.  For the moment
  		 * we keep them separate from the restriction clauses.  Note that this
  		 * step finds only "loose" join clauses that have not been merged into
  		 * EquivalenceClasses.  Also, collect join OR clauses for later.
  		 */
  		MemSet(&jclauseset, 0, sizeof(jclauseset));
  		match_join_clauses_to_index(root, rel, index,
  									&jclauseset, &joinorclauses);
  
  		/*
  		 * Look for EquivalenceClasses that can generate joinclauses matching
  		 * the index.
  		 */
  		MemSet(&eclauseset, 0, sizeof(eclauseset));
  		match_eclass_clauses_to_index(root, index,
  									  &eclauseset);
  
  		/*
  		 * If we found any plain or eclass join clauses, build parameterized
  		 * index paths using them.
  		 */
  		if (jclauseset.nonempty || eclauseset.nonempty)
  			consider_index_join_clauses(root, rel, index,
  										&rclauseset,
  										&jclauseset,
  										&eclauseset,
  										&bitjoinpaths);
  	}
  
  	if (root->hasVLEJoinRTE)
  		return;
  
  	/*
  	 * Generate BitmapOrPaths for any suitable OR-clauses present in the
  	 * restriction list.  Add these to bitindexpaths.
  	 */
  	indexpaths = generate_bitmap_or_paths(root, rel,
  										  rel->baserestrictinfo, NIL);
  	bitindexpaths = list_concat(bitindexpaths, indexpaths);
  
  	/*
  	 * Likewise, generate BitmapOrPaths for any suitable OR-clauses present in
  	 * the joinclause list.  Add these to bitjoinpaths.
  	 */
  	indexpaths = generate_bitmap_or_paths(root, rel,
  									   joinorclauses, rel->baserestrictinfo);
  	bitjoinpaths = list_concat(bitjoinpaths, indexpaths);
  
  	/*
  	 * If we found anything usable, generate a BitmapHeapPath for the most
  	 * promising combination of restriction bitmap index paths.  Note there
  	 * will be only one such path no matter how many indexes exist.  This
  	 * should be sufficient since there's basically only one figure of merit
  	 * (total cost) for such a path.
  	 */
  	if (bitindexpaths != NIL)
  	{
  		Path	   *bitmapqual;
  		BitmapHeapPath *bpath;
  
  		bitmapqual = choose_bitmap_and(root, rel, bitindexpaths);
  		bpath = create_bitmap_heap_path(root, rel, bitmapqual,
  										rel->lateral_relids, 1.0);
  		add_path(rel, (Path *) bpath);
  	}
  
  	/*
  	 * Likewise, if we found anything usable, generate BitmapHeapPaths for the
  	 * most promising combinations of join bitmap index paths.  Our strategy
  	 * is to generate one such path for each distinct parameterization seen
  	 * among the available bitmap index paths.  This may look pretty
  	 * expensive, but usually there won't be very many distinct
  	 * parameterizations.  (This logic is quite similar to that in
  	 * consider_index_join_clauses, but we're working with whole paths not
  	 * individual clauses.)
  	 */
  	if (bitjoinpaths != NIL)
  	{
  		List	   *path_outer;
  		List	   *all_path_outers;
  		ListCell   *lc;
  
  		/*
  		 * path_outer holds the parameterization of each path in bitjoinpaths
  		 * (to save recalculating that several times), while all_path_outers
  		 * holds all distinct parameterization sets.
  		 */
  		path_outer = all_path_outers = NIL;
  		foreach(lc, bitjoinpaths)
  		{
  			Path	   *path = (Path *) lfirst(lc);
  			Relids		required_outer;
  
  			required_outer = get_bitmap_tree_required_outer(path);
  			path_outer = lappend(path_outer, required_outer);
  			if (!bms_equal_any(required_outer, all_path_outers))
  				all_path_outers = lappend(all_path_outers, required_outer);
  		}
  
  		/* Now, for each distinct parameterization set ... */
  		foreach(lc, all_path_outers)
  		{
  			Relids		max_outers = (Relids) lfirst(lc);
  			List	   *this_path_set;
  			Path	   *bitmapqual;
  			Relids		required_outer;
  			double		loop_count;
  			BitmapHeapPath *bpath;
  			ListCell   *lcp;
  			ListCell   *lco;
  
  			/* Identify all the bitmap join paths needing no more than that */
  			this_path_set = NIL;
  			forboth(lcp, bitjoinpaths, lco, path_outer)
  			{
  				Path	   *path = (Path *) lfirst(lcp);
  				Relids		p_outers = (Relids) lfirst(lco);
  
  				if (bms_is_subset(p_outers, max_outers))
  					this_path_set = lappend(this_path_set, path);
  			}
  
  			/*
  			 * Add in restriction bitmap paths, since they can be used
  			 * together with any join paths.
  			 */
  			this_path_set = list_concat(this_path_set, bitindexpaths);
  
  			/* Select best AND combination for this parameterization */
  			bitmapqual = choose_bitmap_and(root, rel, this_path_set);
  
  			/* And push that path into the mix */
  			required_outer = get_bitmap_tree_required_outer(bitmapqual);
  			loop_count = get_loop_count(root, rel->relid, required_outer);
  			bpath = create_bitmap_heap_path(root, rel, bitmapqual,
  											required_outer, loop_count);
  			add_path(rel, (Path *) bpath);
  		}
  	}
  }
  
  /*
   * consider_index_join_clauses
   *	  Given sets of join clauses for an index, decide which parameterized
   *	  index paths to build.
   *
   * Plain indexpaths are sent directly to add_path, while potential
   * bitmap indexpaths are added to *bitindexpaths for later processing.
   *
   * 'rel' is the index's heap relation
   * 'index' is the index for which we want to generate paths
   * 'rclauseset' is the collection of indexable restriction clauses
   * 'jclauseset' is the collection of indexable simple join clauses
   * 'eclauseset' is the collection of indexable clauses from EquivalenceClasses
   * '*bitindexpaths' is the list to add bitmap paths to
   */
  static void
  consider_index_join_clauses(PlannerInfo *root, RelOptInfo *rel,
  							IndexOptInfo *index,
  							IndexClauseSet *rclauseset,
  							IndexClauseSet *jclauseset,
  							IndexClauseSet *eclauseset,
  							List **bitindexpaths)
  {
  	int			considered_clauses = 0;
  	List	   *considered_relids = NIL;
  	int			indexcol;
  
  	/*
  	 * The strategy here is to identify every potentially useful set of outer
  	 * rels that can provide indexable join clauses.  For each such set,
  	 * select all the join clauses available from those outer rels, add on all
  	 * the indexable restriction clauses, and generate plain and/or bitmap
  	 * index paths for that set of clauses.  This is based on the assumption
  	 * that it's always better to apply a clause as an indexqual than as a
  	 * filter (qpqual); which is where an available clause would end up being
  	 * applied if we omit it from the indexquals.
  	 *
  	 * This looks expensive, but in most practical cases there won't be very
  	 * many distinct sets of outer rels to consider.  As a safety valve when
  	 * that's not true, we use a heuristic: limit the number of outer rel sets
  	 * considered to a multiple of the number of clauses considered.  (We'll
  	 * always consider using each individual join clause, though.)
  	 *
  	 * For simplicity in selecting relevant clauses, we represent each set of
  	 * outer rels as a maximum set of clause_relids --- that is, the indexed
  	 * relation itself is also included in the relids set.  considered_relids
  	 * lists all relids sets we've already tried.
  	 */
  	for (indexcol = 0; indexcol < index->ncolumns; indexcol++)
  	{
  		/* Consider each applicable simple join clause */
  		considered_clauses += list_length(jclauseset->indexclauses[indexcol]);
  		consider_index_join_outer_rels(root, rel, index,
  									   rclauseset, jclauseset, eclauseset,
  									   bitindexpaths,
  									   jclauseset->indexclauses[indexcol],
  									   considered_clauses,
  									   &considered_relids);
  		/* Consider each applicable eclass join clause */
  		considered_clauses += list_length(eclauseset->indexclauses[indexcol]);
  		consider_index_join_outer_rels(root, rel, index,
  									   rclauseset, jclauseset, eclauseset,
  									   bitindexpaths,
  									   eclauseset->indexclauses[indexcol],
  									   considered_clauses,
  									   &considered_relids);
  	}
  }
  
  /*
   * consider_index_join_outer_rels
   *	  Generate parameterized paths based on clause relids in the clause list.
   *
   * Workhorse for consider_index_join_clauses; see notes therein for rationale.
   *
   * 'rel', 'index', 'rclauseset', 'jclauseset', 'eclauseset', and
   *		'bitindexpaths' as above
   * 'indexjoinclauses' is a list of RestrictInfos for join clauses
   * 'considered_clauses' is the total number of clauses considered (so far)
   * '*considered_relids' is a list of all relids sets already considered
   */
  static void
  consider_index_join_outer_rels(PlannerInfo *root, RelOptInfo *rel,
  							   IndexOptInfo *index,
  							   IndexClauseSet *rclauseset,
  							   IndexClauseSet *jclauseset,
  							   IndexClauseSet *eclauseset,
  							   List **bitindexpaths,
  							   List *indexjoinclauses,
  							   int considered_clauses,
  							   List **considered_relids)
  {
  	ListCell   *lc;
  
  	/* Examine relids of each joinclause in the given list */
  	foreach(lc, indexjoinclauses)
  	{
  		RestrictInfo *rinfo = (RestrictInfo *) lfirst(lc);
  		Relids		clause_relids = rinfo->clause_relids;
  		ListCell   *lc2;
  
  		/* If we already tried its relids set, no need to do so again */
  		if (bms_equal_any(clause_relids, *considered_relids))
  			continue;
  
  		/*
  		 * Generate the union of this clause's relids set with each
  		 * previously-tried set.  This ensures we try this clause along with
  		 * every interesting subset of previous clauses.  However, to avoid
  		 * exponential growth of planning time when there are many clauses,
  		 * limit the number of relid sets accepted to 10 * considered_clauses.
  		 *
  		 * Note: get_join_index_paths adds entries to *considered_relids, but
  		 * it prepends them to the list, so that we won't visit new entries
  		 * during the inner foreach loop.  No real harm would be done if we
  		 * did, since the subset check would reject them; but it would waste
  		 * some cycles.
  		 */
  		foreach(lc2, *considered_relids)
  		{
  			Relids		oldrelids = (Relids) lfirst(lc2);
  
  			/*
  			 * If either is a subset of the other, no new set is possible.
  			 * This isn't a complete test for redundancy, but it's easy and
  			 * cheap.  get_join_index_paths will check more carefully if we
  			 * already generated the same relids set.
  			 */
  			if (bms_subset_compare(clause_relids, oldrelids) != BMS_DIFFERENT)
  				continue;
  
  			/*
  			 * If this clause was derived from an equivalence class, the
  			 * clause list may contain other clauses derived from the same
  			 * eclass.  We should not consider that combining this clause with
  			 * one of those clauses generates a usefully different
  			 * parameterization; so skip if any clause derived from the same
  			 * eclass would already have been included when using oldrelids.
  			 */
  			if (rinfo->parent_ec &&
  				eclass_already_used(rinfo->parent_ec, oldrelids,
  									indexjoinclauses))
  				continue;
  
  			/*
  			 * If the number of relid sets considered exceeds our heuristic
  			 * limit, stop considering combinations of clauses.  We'll still
  			 * consider the current clause alone, though (below this loop).
  			 */
  			if (list_length(*considered_relids) >= 10 * considered_clauses)
  				break;
  
  			/* OK, try the union set */
  			get_join_index_paths(root, rel, index,
  								 rclauseset, jclauseset, eclauseset,
  								 bitindexpaths,
  								 bms_union(clause_relids, oldrelids),
  								 considered_relids);
  		}
  
  		/* Also try this set of relids by itself */
  		get_join_index_paths(root, rel, index,
  							 rclauseset, jclauseset, eclauseset,
  							 bitindexpaths,
  							 clause_relids,
  							 considered_relids);
  	}
  }
  
  /*
   * get_join_index_paths
   *	  Generate index paths using clauses from the specified outer relations.
   *	  In addition to generating paths, relids is added to *considered_relids
   *	  if not already present.
   *
   * Workhorse for consider_index_join_clauses; see notes therein for rationale.
   *
   * 'rel', 'index', 'rclauseset', 'jclauseset', 'eclauseset',
   *		'bitindexpaths', 'considered_relids' as above
   * 'relids' is the current set of relids to consider (the target rel plus
   *		one or more outer rels)
   */
  static void
  get_join_index_paths(PlannerInfo *root, RelOptInfo *rel,
  					 IndexOptInfo *index,
  					 IndexClauseSet *rclauseset,
  					 IndexClauseSet *jclauseset,
  					 IndexClauseSet *eclauseset,
  					 List **bitindexpaths,
  					 Relids relids,
  					 List **considered_relids)
  {
  	IndexClauseSet clauseset;
  	int			indexcol;
  
  	/* If we already considered this relids set, don't repeat the work */
  	if (bms_equal_any(relids, *considered_relids))
  		return;
  
  	/* Identify indexclauses usable with this relids set */
  	MemSet(&clauseset, 0, sizeof(clauseset));
  
  	for (indexcol = 0; indexcol < index->ncolumns; indexcol++)
  	{
  		ListCell   *lc;
  
  		/* First find applicable simple join clauses */
  		foreach(lc, jclauseset->indexclauses[indexcol])
  		{
  			RestrictInfo *rinfo = (RestrictInfo *) lfirst(lc);
  
  			if (bms_is_subset(rinfo->clause_relids, relids))
  				clauseset.indexclauses[indexcol] =
  					lappend(clauseset.indexclauses[indexcol], rinfo);
  		}
  
  		/*
  		 * Add applicable eclass join clauses.  The clauses generated for each
  		 * column are redundant (cf generate_implied_equalities_for_column),
  		 * so we need at most one.  This is the only exception to the general
  		 * rule of using all available index clauses.
  		 */
  		foreach(lc, eclauseset->indexclauses[indexcol])
  		{
  			RestrictInfo *rinfo = (RestrictInfo *) lfirst(lc);
  
  			if (bms_is_subset(rinfo->clause_relids, relids))
  			{
  				clauseset.indexclauses[indexcol] =
  					lappend(clauseset.indexclauses[indexcol], rinfo);
  				break;
  			}
  		}
  
  		/* Add restriction clauses (this is nondestructive to rclauseset) */
  		clauseset.indexclauses[indexcol] =
  			list_concat(clauseset.indexclauses[indexcol],
  						rclauseset->indexclauses[indexcol]);
  
  		if (clauseset.indexclauses[indexcol] != NIL)
  			clauseset.nonempty = true;
  	}
  
  	/* We should have found something, else caller passed silly relids */
  	Assert(clauseset.nonempty);
  
  	/* Build index path(s) using the collected set of clauses */
  	get_index_paths(root, rel, index, &clauseset, bitindexpaths);
  
  	/*
  	 * Remember we considered paths for this set of relids.  We use lcons not
  	 * lappend to avoid confusing the loop in consider_index_join_outer_rels.
  	 */
  	*considered_relids = lcons(relids, *considered_relids);
  }
  
  /*
   * eclass_already_used
   *		True if any join clause usable with oldrelids was generated from
   *		the specified equivalence class.
   */
  static bool
  eclass_already_used(EquivalenceClass *parent_ec, Relids oldrelids,
  					List *indexjoinclauses)
  {
  	ListCell   *lc;
  
  	foreach(lc, indexjoinclauses)
  	{
  		RestrictInfo *rinfo = (RestrictInfo *) lfirst(lc);
  
  		if (rinfo->parent_ec == parent_ec &&
  			bms_is_subset(rinfo->clause_relids, oldrelids))
  			return true;
  	}
  	return false;
  }
  
  /*
   * bms_equal_any
   *		True if relids is bms_equal to any member of relids_list
   *
   * Perhaps this should be in bitmapset.c someday.
   */
  static bool
  bms_equal_any(Relids relids, List *relids_list)
  {
  	ListCell   *lc;
  
  	foreach(lc, relids_list)
  	{
  		if (bms_equal(relids, (Relids) lfirst(lc)))
  			return true;
  	}
  	return false;
  }
  
  
  /*
   * get_index_paths
   *	  Given an index and a set of index clauses for it, construct IndexPaths.
   *
   * Plain indexpaths are sent directly to add_path, while potential
   * bitmap indexpaths are added to *bitindexpaths for later processing.
   *
   * This is a fairly simple frontend to build_index_paths().  Its reason for
   * existence is mainly to handle ScalarArrayOpExpr quals properly.  If the
   * index AM supports them natively, we should just include them in simple
   * index paths.  If not, we should exclude them while building simple index
   * paths, and then make a separate attempt to include them in bitmap paths.
   * Furthermore, we should consider excluding lower-order ScalarArrayOpExpr
   * quals so as to create ordered paths.
   */
  static void
  get_index_paths(PlannerInfo *root, RelOptInfo *rel,
  				IndexOptInfo *index, IndexClauseSet *clauses,
  				List **bitindexpaths)
  {
  	List	   *indexpaths;
  	bool		skip_nonnative_saop = false;
  	bool		skip_lower_saop = false;
  	ListCell   *lc;
  
  	/*
  	 * Build simple index paths using the clauses.  Allow ScalarArrayOpExpr
  	 * clauses only if the index AM supports them natively, and skip any such
  	 * clauses for index columns after the first (so that we produce ordered
  	 * paths if possible).
  	 */
  	indexpaths = build_index_paths(root, rel,
  								   index, clauses,
  								   index->predOK,
  								   ST_ANYSCAN,
  								   &skip_nonnative_saop,
  								   &skip_lower_saop);
  
  	/*
  	 * If we skipped any lower-order ScalarArrayOpExprs on an index with an AM
  	 * that supports them, then try again including those clauses.  This will
  	 * produce paths with more selectivity but no ordering.
  	 */
  	if (skip_lower_saop)
  	{
  		indexpaths = list_concat(indexpaths,
  								 build_index_paths(root, rel,
  												   index, clauses,
  												   index->predOK,
  												   ST_ANYSCAN,
  												   &skip_nonnative_saop,
  												   NULL));
  	}
  
  	/*
  	 * Submit all the ones that can form plain IndexScan plans to add_path. (A
  	 * plain IndexPath can represent either a plain IndexScan or an
  	 * IndexOnlyScan, but for our purposes here that distinction does not
  	 * matter.  However, some of the indexes might support only bitmap scans,
  	 * and those we mustn't submit to add_path here.)
  	 *
  	 * Also, pick out the ones that are usable as bitmap scans.  For that, we
  	 * must discard indexes that don't support bitmap scans, and we also are
  	 * only interested in paths that have some selectivity; we should discard
  	 * anything that was generated solely for ordering purposes.
  	 */
  	foreach(lc, indexpaths)
  	{
  		IndexPath  *ipath = (IndexPath *) lfirst(lc);
  
  		if (index->amhasgettuple)
  			add_path(rel, (Path *) ipath);
  
  		if (index->amhasgetbitmap &&
  			(ipath->path.pathkeys == NIL ||
  			 ipath->indexselectivity < 1.0))
  			*bitindexpaths = lappend(*bitindexpaths, ipath);
  	}
  
  	/*
  	 * If there were ScalarArrayOpExpr clauses that the index can't handle
  	 * natively, generate bitmap scan paths relying on executor-managed
  	 * ScalarArrayOpExpr.
  	 */
  	if (skip_nonnative_saop)
  	{
  		indexpaths = build_index_paths(root, rel,
  									   index, clauses,
  									   false,
  									   ST_BITMAPSCAN,
  									   NULL,
  									   NULL);
  		*bitindexpaths = list_concat(*bitindexpaths, indexpaths);
  	}
  }
  
  /*
   * build_index_paths
   *	  Given an index and a set of index clauses for it, construct zero
   *	  or more IndexPaths.
   *
   * We return a list of paths because (1) this routine checks some cases
   * that should cause us to not generate any IndexPath, and (2) in some
   * cases we want to consider both a forward and a backward scan, so as
   * to obtain both sort orders.  Note that the paths are just returned
   * to the caller and not immediately fed to add_path().
   *
   * At top level, useful_predicate should be exactly the index's predOK flag
   * (ie, true if it has a predicate that was proven from the restriction
   * clauses).  When working on an arm of an OR clause, useful_predicate
   * should be true if the predicate required the current OR list to be proven.
   * Note that this routine should never be called at all if the index has an
   * unprovable predicate.
   *
   * scantype indicates whether we want to create plain indexscans, bitmap
   * indexscans, or both.  When it's ST_BITMAPSCAN, we will not consider
   * index ordering while deciding if a Path is worth generating.
   *
   * If skip_nonnative_saop is non-NULL, we ignore ScalarArrayOpExpr clauses
   * unless the index AM supports them directly, and we set *skip_nonnative_saop
   * to TRUE if we found any such clauses (caller must initialize the variable
   * to FALSE).  If it's NULL, we do not ignore ScalarArrayOpExpr clauses.
   *
   * If skip_lower_saop is non-NULL, we ignore ScalarArrayOpExpr clauses for
   * non-first index columns, and we set *skip_lower_saop to TRUE if we found
   * any such clauses (caller must initialize the variable to FALSE).  If it's
   * NULL, we do not ignore non-first ScalarArrayOpExpr clauses, but they will
   * result in considering the scan's output to be unordered.
   *
   * 'rel' is the index's heap relation
   * 'index' is the index for which we want to generate paths
   * 'clauses' is the collection of indexable clauses (RestrictInfo nodes)
   * 'useful_predicate' indicates whether the index has a useful predicate
   * 'scantype' indicates whether we need plain or bitmap scan support
   * 'skip_nonnative_saop' indicates whether to accept SAOP if index AM doesn't
   * 'skip_lower_saop' indicates whether to accept non-first-column SAOP
   */
  static List *
  build_index_paths(PlannerInfo *root, RelOptInfo *rel,
  				  IndexOptInfo *index, IndexClauseSet *clauses,
  				  bool useful_predicate,
  				  ScanTypeControl scantype,
  				  bool *skip_nonnative_saop,
  				  bool *skip_lower_saop)
  {
  	List	   *result = NIL;
  	IndexPath  *ipath;
  	List	   *index_clauses;
  	List	   *clause_columns;
  	Relids		outer_relids;
  	double		loop_count;
  	List	   *orderbyclauses;
  	List	   *orderbyclausecols;
  	List	   *index_pathkeys;
  	List	   *useful_pathkeys;
  	bool		found_lower_saop_clause;
  	bool		pathkeys_possibly_useful;
  	bool		index_is_ordered;
  	bool		index_only_scan;
  	int			indexcol;
  
  	/*
  	 * Check that index supports the desired scan type(s)
  	 */
  	switch (scantype)
  	{
  		case ST_INDEXSCAN:
  			if (!index->amhasgettuple)
  				return NIL;
  			break;
  		case ST_BITMAPSCAN:
  			if (!index->amhasgetbitmap)
  				return NIL;
  			break;
  		case ST_ANYSCAN:
  			/* either or both are OK */
  			break;
  	}
  
  	/*
  	 * 1. Collect the index clauses into a single list.
  	 *
  	 * We build a list of RestrictInfo nodes for clauses to be used with this
  	 * index, along with an integer list of the index column numbers (zero
  	 * based) that each clause should be used with.  The clauses are ordered
  	 * by index key, so that the column numbers form a nondecreasing sequence.
  	 * (This order is depended on by btree and possibly other places.)	The
  	 * lists can be empty, if the index AM allows that.
  	 *
  	 * found_lower_saop_clause is set true if we accept a ScalarArrayOpExpr
  	 * index clause for a non-first index column.  This prevents us from
  	 * assuming that the scan result is ordered.  (Actually, the result is
  	 * still ordered if there are equality constraints for all earlier
  	 * columns, but it seems too expensive and non-modular for this code to be
  	 * aware of that refinement.)
  	 *
  	 * We also build a Relids set showing which outer rels are required by the
  	 * selected clauses.  Any lateral_relids are included in that, but not
  	 * otherwise accounted for.
  	 */
  	index_clauses = NIL;
  	clause_columns = NIL;
  	found_lower_saop_clause = false;
  	outer_relids = bms_copy(rel->lateral_relids);
  	for (indexcol = 0; indexcol < index->ncolumns; indexcol++)
  	{
  		ListCell   *lc;
  
  		foreach(lc, clauses->indexclauses[indexcol])
  		{
  			RestrictInfo *rinfo = (RestrictInfo *) lfirst(lc);
  
  			if (IsA(rinfo->clause, ScalarArrayOpExpr))
  			{
  				if (!index->amsearcharray)
  				{
  					if (skip_nonnative_saop)
  					{
  						/* Ignore because not supported by index */
  						*skip_nonnative_saop = true;
  						continue;
  					}
  					/* Caller had better intend this only for bitmap scan */
  					Assert(scantype == ST_BITMAPSCAN);
  				}
  				if (indexcol > 0)
  				{
  					if (skip_lower_saop)
  					{
  						/* Caller doesn't want to lose index ordering */
  						*skip_lower_saop = true;
  						continue;
  					}
  					found_lower_saop_clause = true;
  				}
  			}
  			index_clauses = lappend(index_clauses, rinfo);
  			clause_columns = lappend_int(clause_columns, indexcol);
  			outer_relids = bms_add_members(outer_relids,
  										   rinfo->clause_relids);
  		}
  
  		/*
  		 * If no clauses match the first index column, check for amoptionalkey
  		 * restriction.  We can't generate a scan over an index with
  		 * amoptionalkey = false unless there's at least one index clause.
  		 * (When working on columns after the first, this test cannot fail. It
  		 * is always okay for columns after the first to not have any
  		 * clauses.)
  		 */
  		if (index_clauses == NIL && !index->amoptionalkey)
  			return NIL;
  	}
  
  	/* We do not want the index's rel itself listed in outer_relids */
  	outer_relids = bms_del_member(outer_relids, rel->relid);
  	/* Enforce convention that outer_relids is exactly NULL if empty */
  	if (bms_is_empty(outer_relids))
  		outer_relids = NULL;
  
  	/* Compute loop_count for cost estimation purposes */
  	loop_count = get_loop_count(root, rel->relid, outer_relids);
  
  	/*
  	 * 2. Compute pathkeys describing index's ordering, if any, then see how
  	 * many of them are actually useful for this query.  This is not relevant
  	 * if we are only trying to build bitmap indexscans, nor if we have to
  	 * assume the scan is unordered.
  	 */
  	pathkeys_possibly_useful = (scantype != ST_BITMAPSCAN &&
  								!found_lower_saop_clause &&
  								has_useful_pathkeys(root, rel));
  	index_is_ordered = (index->sortopfamily != NULL);
  	if (index_is_ordered && pathkeys_possibly_useful)
  	{
  		index_pathkeys = build_index_pathkeys(root, index,
  											  ForwardScanDirection);
  		useful_pathkeys = truncate_useless_pathkeys(root, rel,
  													index_pathkeys);
  		orderbyclauses = NIL;
  		orderbyclausecols = NIL;
  	}
  	else if (index->amcanorderbyop && pathkeys_possibly_useful)
  	{
  		/* see if we can generate ordering operators for query_pathkeys */
  		match_pathkeys_to_index(index, root->query_pathkeys,
  								&orderbyclauses,
  								&orderbyclausecols);
  		if (orderbyclauses)
  			useful_pathkeys = root->query_pathkeys;
  		else
  			useful_pathkeys = NIL;
  	}
  	else
  	{
  		useful_pathkeys = NIL;
  		orderbyclauses = NIL;
  		orderbyclausecols = NIL;
  	}
  
  	/*
  	 * 3. Check if an index-only scan is possible.  If we're not building
  	 * plain indexscans, this isn't relevant since bitmap scans don't support
  	 * index data retrieval anyway.
  	 */
  	index_only_scan = (scantype != ST_BITMAPSCAN &&
  					   check_index_only(rel, index,
  										index_clauses, clause_columns));
  
  	/*
  	 * 4. Generate an indexscan path if there are relevant restriction clauses
  	 * in the current clauses, OR the index ordering is potentially useful for
  	 * later merging or final output ordering, OR the index has a useful
  	 * predicate, OR an index-only scan is possible.
  	 */
  	if (index_clauses != NIL || useful_pathkeys != NIL || useful_predicate ||
  		index_only_scan)
  	{
  		ipath = create_index_path(root, index,
  								  index_clauses,
  								  clause_columns,
  								  orderbyclauses,
  								  orderbyclausecols,
  								  useful_pathkeys,
  								  index_is_ordered ?
  								  ForwardScanDirection :
  								  NoMovementScanDirection,
  								  index_only_scan,
  								  outer_relids,
  								  loop_count);
  		result = lappend(result, ipath);
  	}
  
  	/*
  	 * 5. If the index is ordered, a backwards scan might be interesting.
  	 */
  	if (index_is_ordered && pathkeys_possibly_useful)
  	{
  		index_pathkeys = build_index_pathkeys(root, index,
  											  BackwardScanDirection);
  		useful_pathkeys = truncate_useless_pathkeys(root, rel,
  													index_pathkeys);
  		if (useful_pathkeys != NIL)
  		{
  			ipath = create_index_path(root, index,
  									  index_clauses,
  									  clause_columns,
  									  NIL,
  									  NIL,
  									  useful_pathkeys,
  									  BackwardScanDirection,
  									  index_only_scan,
  									  outer_relids,
  									  loop_count);
  			result = lappend(result, ipath);
  		}
  	}
  
  	return result;
  }
  
  /*
   * build_paths_for_OR
   *	  Given a list of restriction clauses from one arm of an OR clause,
   *	  construct all matching IndexPaths for the relation.
   *
   * Here we must scan all indexes of the relation, since a bitmap OR tree
   * can use multiple indexes.
   *
   * The caller actually supplies two lists of restriction clauses: some
   * "current" ones and some "other" ones.  Both lists can be used freely
   * to match keys of the index, but an index must use at least one of the
   * "current" clauses to be considered usable.  The motivation for this is
   * examples like
   *		WHERE (x = 42) AND (... OR (y = 52 AND z = 77) OR ....)
   * While we are considering the y/z subclause of the OR, we can use "x = 42"
   * as one of the available index conditions; but we shouldn't match the
   * subclause to any index on x alone, because such a Path would already have
   * been generated at the upper level.  So we could use an index on x,y,z
   * or an index on x,y for the OR subclause, but not an index on just x.
   * When dealing with a partial index, a match of the index predicate to
   * one of the "current" clauses also makes the index usable.
   *
   * 'rel' is the relation for which we want to generate index paths
   * 'clauses' is the current list of clauses (RestrictInfo nodes)
   * 'other_clauses' is the list of additional upper-level clauses
   */
  static List *
  build_paths_for_OR(PlannerInfo *root, RelOptInfo *rel,
  				   List *clauses, List *other_clauses)
  {
  	List	   *result = NIL;
  	List	   *all_clauses = NIL;		/* not computed till needed */
  	ListCell   *lc;
  
  	foreach(lc, rel->indexlist)
  	{
  		IndexOptInfo *index = (IndexOptInfo *) lfirst(lc);
  		IndexClauseSet clauseset;
  		List	   *indexpaths;
  		bool		useful_predicate;
  
  		/* Ignore index if it doesn't support bitmap scans */
  		if (!index->amhasgetbitmap)
  			continue;
  
  		/*
  		 * Ignore partial indexes that do not match the query.  If a partial
  		 * index is marked predOK then we know it's OK.  Otherwise, we have to
  		 * test whether the added clauses are sufficient to imply the
  		 * predicate. If so, we can use the index in the current context.
  		 *
  		 * We set useful_predicate to true iff the predicate was proven using
  		 * the current set of clauses.  This is needed to prevent matching a
  		 * predOK index to an arm of an OR, which would be a legal but
  		 * pointlessly inefficient plan.  (A better plan will be generated by
  		 * just scanning the predOK index alone, no OR.)
  		 */
  		useful_predicate = false;
  		if (index->indpred != NIL)
  		{
  			if (index->predOK)
  			{
  				/* Usable, but don't set useful_predicate */
  			}
  			else
  			{
  				/* Form all_clauses if not done already */
  				if (all_clauses == NIL)
  					all_clauses = list_concat(list_copy(clauses),
  											  other_clauses);
  
  				if (!predicate_implied_by(index->indpred, all_clauses))
  					continue;	/* can't use it at all */
  
  				if (!predicate_implied_by(index->indpred, other_clauses))
  					useful_predicate = true;
  			}
  		}
  
  		/*
  		 * Identify the restriction clauses that can match the index.
  		 */
  		MemSet(&clauseset, 0, sizeof(clauseset));
  		match_clauses_to_index(index, clauses, &clauseset);
  
  		/*
  		 * If no matches so far, and the index predicate isn't useful, we
  		 * don't want it.
  		 */
  		if (!clauseset.nonempty && !useful_predicate)
  			continue;
  
  		/*
  		 * Add "other" restriction clauses to the clauseset.
  		 */
  		match_clauses_to_index(index, other_clauses, &clauseset);
  
  		/*
  		 * Construct paths if possible.
  		 */
  		indexpaths = build_index_paths(root, rel,
  									   index, &clauseset,
  									   useful_predicate,
  									   ST_BITMAPSCAN,
  									   NULL,
  									   NULL);
  		result = list_concat(result, indexpaths);
  	}
  
  	return result;
  }
  
  /*
   * generate_bitmap_or_paths
   *		Look through the list of clauses to find OR clauses, and generate
   *		a BitmapOrPath for each one we can handle that way.  Return a list
   *		of the generated BitmapOrPaths.
   *
   * other_clauses is a list of additional clauses that can be assumed true
   * for the purpose of generating indexquals, but are not to be searched for
   * ORs.  (See build_paths_for_OR() for motivation.)
   */
  static List *
  generate_bitmap_or_paths(PlannerInfo *root, RelOptInfo *rel,
  						 List *clauses, List *other_clauses)
  {
  	List	   *result = NIL;
  	List	   *all_clauses;
  	ListCell   *lc;
  
  	/*
  	 * We can use both the current and other clauses as context for
  	 * build_paths_for_OR; no need to remove ORs from the lists.
  	 */
  	all_clauses = list_concat(list_copy(clauses), other_clauses);
  
  	foreach(lc, clauses)
  	{
  		RestrictInfo *rinfo = (RestrictInfo *) lfirst(lc);
  		List	   *pathlist;
  		Path	   *bitmapqual;
  		ListCell   *j;
  
  		Assert(IsA(rinfo, RestrictInfo));
  		/* Ignore RestrictInfos that aren't ORs */
  		if (!restriction_is_or_clause(rinfo))
  			continue;
  
  		/*
  		 * We must be able to match at least one index to each of the arms of
  		 * the OR, else we can't use it.
  		 */
  		pathlist = NIL;
  		foreach(j, ((BoolExpr *) rinfo->orclause)->args)
  		{
  			Node	   *orarg = (Node *) lfirst(j);
  			List	   *indlist;
  
  			/* OR arguments should be ANDs or sub-RestrictInfos */
  			if (and_clause(orarg))
  			{
  				List	   *andargs = ((BoolExpr *) orarg)->args;
  
  				indlist = build_paths_for_OR(root, rel,
  											 andargs,
  											 all_clauses);
  
  				/* Recurse in case there are sub-ORs */
  				indlist = list_concat(indlist,
  									  generate_bitmap_or_paths(root, rel,
  															   andargs,
  															   all_clauses));
  			}
  			else
  			{
  				List	   *orargs;
  
  				Assert(IsA(orarg, RestrictInfo));
  				Assert(!restriction_is_or_clause((RestrictInfo *) orarg));
  				orargs = list_make1(orarg);
  
  				indlist = build_paths_for_OR(root, rel,
  											 orargs,
  											 all_clauses);
  			}
  
  			/*
  			 * If nothing matched this arm, we can't do anything with this OR
  			 * clause.
  			 */
  			if (indlist == NIL)
  			{
  				pathlist = NIL;
  				break;
  			}
  
  			/*
  			 * OK, pick the most promising AND combination, and add it to
  			 * pathlist.
  			 */
  			bitmapqual = choose_bitmap_and(root, rel, indlist);
  			pathlist = lappend(pathlist, bitmapqual);
  		}
  
  		/*
  		 * If we have a match for every arm, then turn them into a
  		 * BitmapOrPath, and add to result list.
  		 */
  		if (pathlist != NIL)
  		{
  			bitmapqual = (Path *) create_bitmap_or_path(root, rel, pathlist);
  			result = lappend(result, bitmapqual);
  		}
  	}
  
  	return result;
  }
  
  
  /*
   * choose_bitmap_and
   *		Given a nonempty list of bitmap paths, AND them into one path.
   *
   * This is a nontrivial decision since we can legally use any subset of the
   * given path set.  We want to choose a good tradeoff between selectivity
   * and cost of computing the bitmap.
   *
   * The result is either a single one of the inputs, or a BitmapAndPath
   * combining multiple inputs.
   */
  static Path *
  choose_bitmap_and(PlannerInfo *root, RelOptInfo *rel, List *paths)
  {
  	int			npaths = list_length(paths);
  	PathClauseUsage **pathinfoarray;
  	PathClauseUsage *pathinfo;
  	List	   *clauselist;
  	List	   *bestpaths = NIL;
  	Cost		bestcost = 0;
  	int			i,
  				j;
  	ListCell   *l;
  
  	Assert(npaths > 0);			/* else caller error */
  	if (npaths == 1)
  		return (Path *) linitial(paths);		/* easy case */
  
  	/*
  	 * In theory we should consider every nonempty subset of the given paths.
  	 * In practice that seems like overkill, given the crude nature of the
  	 * estimates, not to mention the possible effects of higher-level AND and
  	 * OR clauses.  Moreover, it's completely impractical if there are a large
  	 * number of paths, since the work would grow as O(2^N).
  	 *
  	 * As a heuristic, we first check for paths using exactly the same sets of
  	 * WHERE clauses + index predicate conditions, and reject all but the
  	 * cheapest-to-scan in any such group.  This primarily gets rid of indexes
  	 * that include the interesting columns but also irrelevant columns.  (In
  	 * situations where the DBA has gone overboard on creating variant
  	 * indexes, this can make for a very large reduction in the number of
  	 * paths considered further.)
  	 *
  	 * We then sort the surviving paths with the cheapest-to-scan first, and
  	 * for each path, consider using that path alone as the basis for a bitmap
  	 * scan.  Then we consider bitmap AND scans formed from that path plus
  	 * each subsequent (higher-cost) path, adding on a subsequent path if it
  	 * results in a reduction in the estimated total scan cost. This means we
  	 * consider about O(N^2) rather than O(2^N) path combinations, which is
  	 * quite tolerable, especially given than N is usually reasonably small
  	 * because of the prefiltering step.  The cheapest of these is returned.
  	 *
  	 * We will only consider AND combinations in which no two indexes use the
  	 * same WHERE clause.  This is a bit of a kluge: it's needed because
  	 * costsize.c and clausesel.c aren't very smart about redundant clauses.
  	 * They will usually double-count the redundant clauses, producing a
  	 * too-small selectivity that makes a redundant AND step look like it
  	 * reduces the total cost.  Perhaps someday that code will be smarter and
  	 * we can remove this limitation.  (But note that this also defends
  	 * against flat-out duplicate input paths, which can happen because
  	 * match_join_clauses_to_index will find the same OR join clauses that
  	 * extract_restriction_or_clauses has pulled OR restriction clauses out
  	 * of.)
  	 *
  	 * For the same reason, we reject AND combinations in which an index
  	 * predicate clause duplicates another clause.  Here we find it necessary
  	 * to be even stricter: we'll reject a partial index if any of its
  	 * predicate clauses are implied by the set of WHERE clauses and predicate
  	 * clauses used so far.  This covers cases such as a condition "x = 42"
  	 * used with a plain index, followed by a clauseless scan of a partial
  	 * index "WHERE x >= 40 AND x < 50".  The partial index has been accepted
  	 * only because "x = 42" was present, and so allowing it would partially
  	 * double-count selectivity.  (We could use predicate_implied_by on
  	 * regular qual clauses too, to have a more intelligent, but much more
  	 * expensive, check for redundancy --- but in most cases simple equality
  	 * seems to suffice.)
  	 */
  
  	/*
  	 * Extract clause usage info and detect any paths that use exactly the
  	 * same set of clauses; keep only the cheapest-to-scan of any such groups.
  	 * The surviving paths are put into an array for qsort'ing.
  	 */
  	pathinfoarray = (PathClauseUsage **)
  		palloc(npaths * sizeof(PathClauseUsage *));
  	clauselist = NIL;
  	npaths = 0;
  	foreach(l, paths)
  	{
  		Path	   *ipath = (Path *) lfirst(l);
  
  		pathinfo = classify_index_clause_usage(ipath, &clauselist);
  		for (i = 0; i < npaths; i++)
  		{
  			if (bms_equal(pathinfo->clauseids, pathinfoarray[i]->clauseids))
  				break;
  		}
  		if (i < npaths)
  		{
  			/* duplicate clauseids, keep the cheaper one */
  			Cost		ncost;
  			Cost		ocost;
  			Selectivity nselec;
  			Selectivity oselec;
  
  			cost_bitmap_tree_node(pathinfo->path, &ncost, &nselec);
  			cost_bitmap_tree_node(pathinfoarray[i]->path, &ocost, &oselec);
  			if (ncost < ocost)
  				pathinfoarray[i] = pathinfo;
  		}
  		else
  		{
  			/* not duplicate clauseids, add to array */
  			pathinfoarray[npaths++] = pathinfo;
  		}
  	}
  
  	/* If only one surviving path, we're done */
  	if (npaths == 1)
  		return pathinfoarray[0]->path;
  
  	/* Sort the surviving paths by index access cost */
  	qsort(pathinfoarray, npaths, sizeof(PathClauseUsage *),
  		  path_usage_comparator);
  
  	/*
  	 * For each surviving index, consider it as an "AND group leader", and see
  	 * whether adding on any of the later indexes results in an AND path with
  	 * cheaper total cost than before.  Then take the cheapest AND group.
  	 */
  	for (i = 0; i < npaths; i++)
  	{
  		Cost		costsofar;
  		List	   *qualsofar;
  		Bitmapset  *clauseidsofar;
  		ListCell   *lastcell;
  
  		pathinfo = pathinfoarray[i];
  		paths = list_make1(pathinfo->path);
  		costsofar = bitmap_scan_cost_est(root, rel, pathinfo->path);
  		qualsofar = list_concat(list_copy(pathinfo->quals),
  								list_copy(pathinfo->preds));
  		clauseidsofar = bms_copy(pathinfo->clauseids);
  		lastcell = list_head(paths);	/* for quick deletions */
  
  		for (j = i + 1; j < npaths; j++)
  		{
  			Cost		newcost;
  
  			pathinfo = pathinfoarray[j];
  			/* Check for redundancy */
  			if (bms_overlap(pathinfo->clauseids, clauseidsofar))
  				continue;		/* consider it redundant */
  			if (pathinfo->preds)
  			{
  				bool		redundant = false;
  
  				/* we check each predicate clause separately */
  				foreach(l, pathinfo->preds)
  				{
  					Node	   *np = (Node *) lfirst(l);
  
  					if (predicate_implied_by(list_make1(np), qualsofar))
  					{
  						redundant = true;
  						break;	/* out of inner foreach loop */
  					}
  				}
  				if (redundant)
  					continue;
  			}
  			/* tentatively add new path to paths, so we can estimate cost */
  			paths = lappend(paths, pathinfo->path);
  			newcost = bitmap_and_cost_est(root, rel, paths);
  			if (newcost < costsofar)
  			{
  				/* keep new path in paths, update subsidiary variables */
  				costsofar = newcost;
  				qualsofar = list_concat(qualsofar,
  										list_copy(pathinfo->quals));
  				qualsofar = list_concat(qualsofar,
  										list_copy(pathinfo->preds));
  				clauseidsofar = bms_add_members(clauseidsofar,
  												pathinfo->clauseids);
  				lastcell = lnext(lastcell);
  			}
  			else
  			{
  				/* reject new path, remove it from paths list */
  				paths = list_delete_cell(paths, lnext(lastcell), lastcell);
  			}
  			Assert(lnext(lastcell) == NULL);
  		}
  
  		/* Keep the cheapest AND-group (or singleton) */
  		if (i == 0 || costsofar < bestcost)
  		{
  			bestpaths = paths;
  			bestcost = costsofar;
  		}
  
  		/* some easy cleanup (we don't try real hard though) */
  		list_free(qualsofar);
  	}
  
  	if (list_length(bestpaths) == 1)
  		return (Path *) linitial(bestpaths);	/* no need for AND */
  	return (Path *) create_bitmap_and_path(root, rel, bestpaths);
  }
  
  /* qsort comparator to sort in increasing index access cost order */
  static int
  path_usage_comparator(const void *a, const void *b)
  {
  	PathClauseUsage *pa = *(PathClauseUsage *const *) a;
  	PathClauseUsage *pb = *(PathClauseUsage *const *) b;
  	Cost		acost;
  	Cost		bcost;
  	Selectivity aselec;
  	Selectivity bselec;
  
  	cost_bitmap_tree_node(pa->path, &acost, &aselec);
  	cost_bitmap_tree_node(pb->path, &bcost, &bselec);
  
  	/*
  	 * If costs are the same, sort by selectivity.
  	 */
  	if (acost < bcost)
  		return -1;
  	if (acost > bcost)
  		return 1;
  
  	if (aselec < bselec)
  		return -1;
  	if (aselec > bselec)
  		return 1;
  
  	return 0;
  }
  
  /*
   * Estimate the cost of actually executing a bitmap scan with a single
   * index path (no BitmapAnd, at least not at this level; but it could be
   * a BitmapOr).
   */
  static Cost
  bitmap_scan_cost_est(PlannerInfo *root, RelOptInfo *rel, Path *ipath)
  {
  	BitmapHeapPath bpath;
  	Relids		required_outer;
  
  	/* Identify required outer rels, in case it's a parameterized scan */
  	required_outer = get_bitmap_tree_required_outer(ipath);
  
  	/* Set up a dummy BitmapHeapPath */
  	bpath.path.type = T_BitmapHeapPath;
  	bpath.path.pathtype = T_BitmapHeapScan;
  	bpath.path.parent = rel;
  	bpath.path.pathtarget = rel->reltarget;
  	bpath.path.param_info = get_baserel_parampathinfo(root, rel,
  													  required_outer);
  	bpath.path.pathkeys = NIL;
  	bpath.bitmapqual = ipath;
  
  	cost_bitmap_heap_scan(&bpath.path, root, rel,
  						  bpath.path.param_info,
  						  ipath,
  						  get_loop_count(root, rel->relid, required_outer));
  
  	return bpath.path.total_cost;
  }
  
  /*
   * Estimate the cost of actually executing a BitmapAnd scan with the given
   * inputs.
   */
  static Cost
  bitmap_and_cost_est(PlannerInfo *root, RelOptInfo *rel, List *paths)
  {
  	BitmapAndPath apath;
  	BitmapHeapPath bpath;
  	Relids		required_outer;
  
  	/* Set up a dummy BitmapAndPath */
  	apath.path.type = T_BitmapAndPath;
  	apath.path.pathtype = T_BitmapAnd;
  	apath.path.parent = rel;
  	apath.path.pathtarget = rel->reltarget;
  	apath.path.param_info = NULL;		/* not used in bitmap trees */
  	apath.path.pathkeys = NIL;
  	apath.bitmapquals = paths;
  	cost_bitmap_and_node(&apath, root);
  
  	/* Identify required outer rels, in case it's a parameterized scan */
  	required_outer = get_bitmap_tree_required_outer((Path *) &apath);
  
  	/* Set up a dummy BitmapHeapPath */
  	bpath.path.type = T_BitmapHeapPath;
  	bpath.path.pathtype = T_BitmapHeapScan;
  	bpath.path.parent = rel;
  	bpath.path.pathtarget = rel->reltarget;
  	bpath.path.param_info = get_baserel_parampathinfo(root, rel,
  													  required_outer);
  	bpath.path.pathkeys = NIL;
  	bpath.bitmapqual = (Path *) &apath;
  
  	/* Now we can do cost_bitmap_heap_scan */
  	cost_bitmap_heap_scan(&bpath.path, root, rel,
  						  bpath.path.param_info,
  						  (Path *) &apath,
  						  get_loop_count(root, rel->relid, required_outer));
  
  	return bpath.path.total_cost;
  }
  
  
  /*
   * classify_index_clause_usage
   *		Construct a PathClauseUsage struct describing the WHERE clauses and
   *		index predicate clauses used by the given indexscan path.
   *		We consider two clauses the same if they are equal().
   *
   * At some point we might want to migrate this info into the Path data
   * structure proper, but for the moment it's only needed within
   * choose_bitmap_and().
   *
   * *clauselist is used and expanded as needed to identify all the distinct
   * clauses seen across successive calls.  Caller must initialize it to NIL
   * before first call of a set.
   */
  static PathClauseUsage *
  classify_index_clause_usage(Path *path, List **clauselist)
  {
  	PathClauseUsage *result;
  	Bitmapset  *clauseids;
  	ListCell   *lc;
  
  	result = (PathClauseUsage *) palloc(sizeof(PathClauseUsage));
  	result->path = path;
  
  	/* Recursively find the quals and preds used by the path */
  	result->quals = NIL;
  	result->preds = NIL;
  	find_indexpath_quals(path, &result->quals, &result->preds);
  
  	/* Build up a bitmapset representing the quals and preds */
  	clauseids = NULL;
  	foreach(lc, result->quals)
  	{
  		Node	   *node = (Node *) lfirst(lc);
  
  		clauseids = bms_add_member(clauseids,
  								   find_list_position(node, clauselist));
  	}
  	foreach(lc, result->preds)
  	{
  		Node	   *node = (Node *) lfirst(lc);
  
  		clauseids = bms_add_member(clauseids,
  								   find_list_position(node, clauselist));
  	}
  	result->clauseids = clauseids;
  
  	return result;
  }
  
  
  /*
   * get_bitmap_tree_required_outer
   *		Find the required outer rels for a bitmap tree (index/and/or)
   *
   * We don't associate any particular parameterization with a BitmapAnd or
   * BitmapOr node; however, the IndexPaths have parameterization info, in
   * their capacity as standalone access paths.  The parameterization required
   * for the bitmap heap scan node is the union of rels referenced in the
   * child IndexPaths.
   */
  static Relids
  get_bitmap_tree_required_outer(Path *bitmapqual)
  {
  	Relids		result = NULL;
  	ListCell   *lc;
  
  	if (IsA(bitmapqual, IndexPath))
  	{
  		return bms_copy(PATH_REQ_OUTER(bitmapqual));
  	}
  	else if (IsA(bitmapqual, BitmapAndPath))
  	{
  		foreach(lc, ((BitmapAndPath *) bitmapqual)->bitmapquals)
  		{
  			result = bms_join(result,
  						get_bitmap_tree_required_outer((Path *) lfirst(lc)));
  		}
  	}
  	else if (IsA(bitmapqual, BitmapOrPath))
  	{
  		foreach(lc, ((BitmapOrPath *) bitmapqual)->bitmapquals)
  		{
  			result = bms_join(result,
  						get_bitmap_tree_required_outer((Path *) lfirst(lc)));
  		}
  	}
  	else
  		elog(ERROR, "unrecognized node type: %d", nodeTag(bitmapqual));
  
  	return result;
  }
  
  
  /*
   * find_indexpath_quals
   *
   * Given the Path structure for a plain or bitmap indexscan, extract lists
   * of all the indexquals and index predicate conditions used in the Path.
   * These are appended to the initial contents of *quals and *preds (hence
   * caller should initialize those to NIL).
   *
   * Note we are not trying to produce an accurate representation of the AND/OR
   * semantics of the Path, but just find out all the base conditions used.
   *
   * The result lists contain pointers to the expressions used in the Path,
   * but all the list cells are freshly built, so it's safe to destructively
   * modify the lists (eg, by concat'ing with other lists).
   */
  static void
  find_indexpath_quals(Path *bitmapqual, List **quals, List **preds)
  {
  	if (IsA(bitmapqual, BitmapAndPath))
  	{
  		BitmapAndPath *apath = (BitmapAndPath *) bitmapqual;
  		ListCell   *l;
  
  		foreach(l, apath->bitmapquals)
  		{
  			find_indexpath_quals((Path *) lfirst(l), quals, preds);
  		}
  	}
  	else if (IsA(bitmapqual, BitmapOrPath))
  	{
  		BitmapOrPath *opath = (BitmapOrPath *) bitmapqual;
  		ListCell   *l;
  
  		foreach(l, opath->bitmapquals)
  		{
  			find_indexpath_quals((Path *) lfirst(l), quals, preds);
  		}
  	}
  	else if (IsA(bitmapqual, IndexPath))
  	{
  		IndexPath  *ipath = (IndexPath *) bitmapqual;
  
  		*quals = list_concat(*quals, get_actual_clauses(ipath->indexclauses));
  		*preds = list_concat(*preds, list_copy(ipath->indexinfo->indpred));
  	}
  	else
  		elog(ERROR, "unrecognized node type: %d", nodeTag(bitmapqual));
  }
  
  
  /*
   * find_list_position
   *		Return the given node's position (counting from 0) in the given
   *		list of nodes.  If it's not equal() to any existing list member,
   *		add it at the end, and return that position.
   */
  static int
  find_list_position(Node *node, List **nodelist)
  {
  	int			i;
  	ListCell   *lc;
  
  	i = 0;
  	foreach(lc, *nodelist)
  	{
  		Node	   *oldnode = (Node *) lfirst(lc);
  
  		if (equal(node, oldnode))
  			return i;
  		i++;
  	}
  
  	*nodelist = lappend(*nodelist, node);
  
  	return i;
  }
  
  /*
   * check_index_only
   *		Determine whether an index-only scan is possible for this index.
   */
  static bool
  check_index_only(RelOptInfo *rel, IndexOptInfo *index, List *index_clauses,
  				 List *clause_columns)
  {
  	bool		result;
  	Bitmapset  *attrs_used = NULL;
  	Bitmapset  *index_canreturn_attrs = NULL;
  	ListCell   *lc;
  	int			i;
  
  	/* Index-only scans must be enabled */
  	if (!enable_indexonlyscan)
  		return false;
  
  	/*
  	 * Check that all needed attributes of the relation are available from the
  	 * index.
  	 */
  
  	/*
  	 * First, identify all the attributes needed for joins or final output.
  	 * Note: we must look at rel's targetlist, not the attr_needed data,
  	 * because attr_needed isn't computed for inheritance child rels.
  	 */
  	pull_varattnos((Node *) rel->reltarget->exprs, rel->relid, &attrs_used);
  
  	/*
  	 * Add all the attributes used by restriction clauses; but consider only
  	 * those clauses not implied by the index predicate, since ones that are
  	 * so implied don't need to be checked explicitly in the plan.
  	 *
  	 * Note: attributes used only in index quals would not be needed at
  	 * runtime either, if we are certain that the index is not lossy.  However
  	 * it'd be complicated to account for that accurately, and it doesn't
  	 * matter in most cases, since we'd conclude that such attributes are
  	 * available from the index anyway.
  	 */
  	foreach(lc, index->indrestrictinfo)
  	{
  		RestrictInfo *rinfo = (RestrictInfo *) lfirst(lc);
  		bool		indexpr;
  		ListCell   *le;
  		ListCell   *lc;
  
  		/*
  		 * Allow index-only scan for index expressions only if there is no use
  		 * of columns which are not index column in both rel->reltarget->exprs
  		 * and index->indrestrictinfo.
  		 */
  		indexpr = false;
  		forboth(le, index_clauses, lc, clause_columns)
  		{
  			if (lfirst(le) == rinfo && index->indexkeys[lfirst_int(lc)] == 0)
  			{
  				indexpr = true;
  				break;
  			}
  		}
  		if (indexpr)
  			continue;
  
  		pull_varattnos((Node *) rinfo->clause, rel->relid, &attrs_used);
  	}
  
  	/*
  	 * Construct a bitmapset of columns that the index can return back in an
  	 * index-only scan.
  	 */
  	for (i = 0; i < index->ncolumns; i++)
  	{
  		int			attno = index->indexkeys[i];
  
  		/*
  		 * For the moment, we just ignore index expressions.  It might be nice
  		 * to do something with them, later.
  		 */
  		if (attno == 0)
  			continue;
  
  		if (index->canreturn[i])
  			index_canreturn_attrs =
  				bms_add_member(index_canreturn_attrs,
  							   attno - FirstLowInvalidHeapAttributeNumber);
  	}
  
  	/* Do we have all the necessary attributes? */
  	result = bms_is_subset(attrs_used, index_canreturn_attrs);
  
  	bms_free(attrs_used);
  	bms_free(index_canreturn_attrs);
  
  	return result;
  }
  
  /*
   * get_loop_count
   *		Choose the loop count estimate to use for costing a parameterized path
   *		with the given set of outer relids.
   *
   * Since we produce parameterized paths before we've begun to generate join
   * relations, it's impossible to predict exactly how many times a parameterized
   * path will be iterated; we don't know the size of the relation that will be
   * on the outside of the nestloop.  However, we should try to account for
   * multiple iterations somehow in costing the path.  The heuristic embodied
   * here is to use the rowcount of the smallest other base relation needed in
   * the join clauses used by the path.  (We could alternatively consider the
   * largest one, but that seems too optimistic.)  This is of course the right
   * answer for single-other-relation cases, and it seems like a reasonable
   * zero-order approximation for multiway-join cases.
   *
   * In addition, we check to see if the other side of each join clause is on
   * the inside of some semijoin that the current relation is on the outside of.
   * If so, the only way that a parameterized path could be used is if the
   * semijoin RHS has been unique-ified, so we should use the number of unique
   * RHS rows rather than using the relation's raw rowcount.
   *
   * Note: for this to work, allpaths.c must establish all baserel size
   * estimates before it begins to compute paths, or at least before it
   * calls create_index_paths().
   */
  static double
  get_loop_count(PlannerInfo *root, Index cur_relid, Relids outer_relids)
  {
  	double		result;
  	int			outer_relid;
  
  	/* For a non-parameterized path, just return 1.0 quickly */
  	if (outer_relids == NULL)
  		return 1.0;
  
  	result = 0.0;
  	outer_relid = -1;
  	while ((outer_relid = bms_next_member(outer_relids, outer_relid)) >= 0)
  	{
  		RelOptInfo *outer_rel;
  		double		rowcount;
  
  		/* Paranoia: ignore bogus relid indexes */
  		if (outer_relid >= root->simple_rel_array_size)
  			continue;
  		outer_rel = root->simple_rel_array[outer_relid];
  		if (outer_rel == NULL)
  			continue;
  		Assert(outer_rel->relid == outer_relid);		/* sanity check on array */
  
  		/* Other relation could be proven empty, if so ignore */
  		if (IS_DUMMY_REL(outer_rel))
  			continue;
  
  		/* Otherwise, rel's rows estimate should be valid by now */
  		Assert(outer_rel->rows > 0);
  
  		/* Check to see if rel is on the inside of any semijoins */
  		rowcount = adjust_rowcount_for_semijoins(root,
  												 cur_relid,
  												 outer_relid,
  												 outer_rel->rows);
  
  		/* Remember smallest row count estimate among the outer rels */
  		if (result == 0.0 || result > rowcount)
  			result = rowcount;
  	}
  	/* Return 1.0 if we found no valid relations (shouldn't happen) */
  	return (result > 0.0) ? result : 1.0;
  }
  
  /*
   * Check to see if outer_relid is on the inside of any semijoin that cur_relid
   * is on the outside of.  If so, replace rowcount with the estimated number of
   * unique rows from the semijoin RHS (assuming that's smaller, which it might
   * not be).  The estimate is crude but it's the best we can do at this stage
   * of the proceedings.
   */
  static double
  adjust_rowcount_for_semijoins(PlannerInfo *root,
  							  Index cur_relid,
  							  Index outer_relid,
  							  double rowcount)
  {
  	ListCell   *lc;
  
  	foreach(lc, root->join_info_list)
  	{
  		SpecialJoinInfo *sjinfo = (SpecialJoinInfo *) lfirst(lc);
  
  		if (sjinfo->jointype == JOIN_SEMI &&
  			bms_is_member(cur_relid, sjinfo->syn_lefthand) &&
  			bms_is_member(outer_relid, sjinfo->syn_righthand))
  		{
  			/* Estimate number of unique-ified rows */
  			double		nraw;
  			double		nunique;
  
  			nraw = approximate_joinrel_size(root, sjinfo->syn_righthand);
  			nunique = estimate_num_groups(root,
  										  sjinfo->semi_rhs_exprs,
  										  nraw,
  										  NULL);
  			if (rowcount > nunique)
  				rowcount = nunique;
  		}
  	}
  	return rowcount;
  }
  
  /*
   * Make an approximate estimate of the size of a joinrel.
   *
   * We don't have enough info at this point to get a good estimate, so we
   * just multiply the base relation sizes together.  Fortunately, this is
   * the right answer anyway for the most common case with a single relation
   * on the RHS of a semijoin.  Also, estimate_num_groups() has only a weak
   * dependency on its input_rows argument (it basically uses it as a clamp).
   * So we might be able to get a fairly decent end result even with a severe
   * overestimate of the RHS's raw size.
   */
  static double
  approximate_joinrel_size(PlannerInfo *root, Relids relids)
  {
  	double		rowcount = 1.0;
  	int			relid;
  
  	relid = -1;
  	while ((relid = bms_next_member(relids, relid)) >= 0)
  	{
  		RelOptInfo *rel;
  
  		/* Paranoia: ignore bogus relid indexes */
  		if (relid >= root->simple_rel_array_size)
  			continue;
  		rel = root->simple_rel_array[relid];
  		if (rel == NULL)
  			continue;
  		Assert(rel->relid == relid);	/* sanity check on array */
  
  		/* Relation could be proven empty, if so ignore */
  		if (IS_DUMMY_REL(rel))
  			continue;
  
  		/* Otherwise, rel's rows estimate should be valid by now */
  		Assert(rel->rows > 0);
  
  		/* Accumulate product */
  		rowcount *= rel->rows;
  	}
  	return rowcount;
  }
  
  
  /****************************************************************************
   *				----  ROUTINES TO CHECK QUERY CLAUSES  ----
   ****************************************************************************/
  
  /*
   * match_restriction_clauses_to_index
   *	  Identify restriction clauses for the rel that match the index.
   *	  Matching clauses are added to *clauseset.
   */
  static void
  match_restriction_clauses_to_index(RelOptInfo *rel, IndexOptInfo *index,
  								   IndexClauseSet *clauseset)
  {
  	/* We can ignore clauses that are implied by the index predicate */
  	match_clauses_to_index(index, index->indrestrictinfo, clauseset);
  }
  
  /*
   * match_join_clauses_to_index
   *	  Identify join clauses for the rel that match the index.
   *	  Matching clauses are added to *clauseset.
   *	  Also, add any potentially usable join OR clauses to *joinorclauses.
   */
  static void
  match_join_clauses_to_index(PlannerInfo *root,
  							RelOptInfo *rel, IndexOptInfo *index,
  							IndexClauseSet *clauseset,
  							List **joinorclauses)
  {
  	ListCell   *lc;
  
  	/* Scan the rel's join clauses */
  	foreach(lc, rel->joininfo)
  	{
  		RestrictInfo *rinfo = (RestrictInfo *) lfirst(lc);
  
  		/* Check if clause can be moved to this rel */
  		if (!join_clause_is_movable_to(rinfo, rel))
  			continue;
  
  		/* Potentially usable, so see if it matches the index or is an OR */
  		if (restriction_is_or_clause(rinfo))
  			*joinorclauses = lappend(*joinorclauses, rinfo);
  		else
  			match_clause_to_index(index, rinfo, clauseset);
  	}
  }
  
  /*
   * match_eclass_clauses_to_index
   *	  Identify EquivalenceClass join clauses for the rel that match the index.
   *	  Matching clauses are added to *clauseset.
   */
  static void
  match_eclass_clauses_to_index(PlannerInfo *root, IndexOptInfo *index,
  							  IndexClauseSet *clauseset)
  {
  	int			indexcol;
  
  	/* No work if rel is not in any such ECs */
  	if (!index->rel->has_eclass_joins)
  		return;
  
  	for (indexcol = 0; indexcol < index->ncolumns; indexcol++)
  	{
  		ec_member_matches_arg arg;
  		List	   *clauses;
  
  		/* Generate clauses, skipping any that join to lateral_referencers */
  		arg.index = index;
  		arg.indexcol = indexcol;
  		clauses = generate_implied_equalities_for_column(root,
  														 index->rel,
  												  ec_member_matches_indexcol,
  														 (void *) &arg,
  											index->rel->lateral_referencers);
  
  		/*
  		 * We have to check whether the results actually do match the index,
  		 * since for non-btree indexes the EC's equality operators might not
  		 * be in the index opclass (cf ec_member_matches_indexcol).
  		 */
  		match_clauses_to_index(index, clauses, clauseset);
  	}
  }
  
  /*
   * match_clauses_to_index
   *	  Perform match_clause_to_index() for each clause in a list.
   *	  Matching clauses are added to *clauseset.
   */
  static void
  match_clauses_to_index(IndexOptInfo *index,
  					   List *clauses,
  					   IndexClauseSet *clauseset)
  {
  	ListCell   *lc;
  
  	foreach(lc, clauses)
  	{
  		RestrictInfo *rinfo = (RestrictInfo *) lfirst(lc);
  
  		Assert(IsA(rinfo, RestrictInfo));
  		match_clause_to_index(index, rinfo, clauseset);
  	}
  }
  
  /*
   * match_clause_to_index
   *	  Test whether a qual clause can be used with an index.
   *
   * If the clause is usable, add it to the appropriate list in *clauseset.
   * *clauseset must be initialized to zeroes before first call.
   *
   * Note: in some circumstances we may find the same RestrictInfos coming from
   * multiple places.  Defend against redundant outputs by refusing to add a
   * clause twice (pointer equality should be a good enough check for this).
   *
   * Note: it's possible that a badly-defined index could have multiple matching
   * columns.  We always select the first match if so; this avoids scenarios
   * wherein we get an inflated idea of the index's selectivity by using the
   * same clause multiple times with different index columns.
   */
  static void
  match_clause_to_index(IndexOptInfo *index,
  					  RestrictInfo *rinfo,
  					  IndexClauseSet *clauseset)
  {
  	int			indexcol;
  
  	for (indexcol = 0; indexcol < index->ncolumns; indexcol++)
  	{
  		if (match_clause_to_indexcol(index,
  									 indexcol,
  									 rinfo))
  		{
  			clauseset->indexclauses[indexcol] =
  				list_append_unique_ptr(clauseset->indexclauses[indexcol],
  									   rinfo);
  			clauseset->nonempty = true;
  			return;
  		}
  	}
  }
  
  /*
   * match_clause_to_indexcol()
   *	  Determines whether a restriction clause matches a column of an index.
   *
   *	  To match an index normally, the clause:
   *
   *	  (1)  must be in the form (indexkey op const) or (const op indexkey);
   *		   and
   *	  (2)  must contain an operator which is in the same family as the index
   *		   operator for this column, or is a "special" operator as recognized
   *		   by match_special_index_operator();
   *		   and
   *	  (3)  must match the collation of the index, if collation is relevant.
   *
   *	  Our definition of "const" is exceedingly liberal: we allow anything that
   *	  doesn't involve a volatile function or a Var of the index's relation.
   *	  In particular, Vars belonging to other relations of the query are
   *	  accepted here, since a clause of that form can be used in a
   *	  parameterized indexscan.  It's the responsibility of higher code levels
   *	  to manage restriction and join clauses appropriately.
   *
   *	  Note: we do need to check for Vars of the index's relation on the
   *	  "const" side of the clause, since clauses like (a.f1 OP (b.f2 OP a.f3))
   *	  are not processable by a parameterized indexscan on a.f1, whereas
   *	  something like (a.f1 OP (b.f2 OP c.f3)) is.
   *
   *	  Presently, the executor can only deal with indexquals that have the
   *	  indexkey on the left, so we can only use clauses that have the indexkey
   *	  on the right if we can commute the clause to put the key on the left.
   *	  We do not actually do the commuting here, but we check whether a
   *	  suitable commutator operator is available.
   *
   *	  If the index has a collation, the clause must have the same collation.
   *	  For collation-less indexes, we assume it doesn't matter; this is
   *	  necessary for cases like "hstore ? text", wherein hstore's operators
   *	  don't care about collation but the clause will get marked with a
   *	  collation anyway because of the text argument.  (This logic is
   *	  embodied in the macro IndexCollMatchesExprColl.)
   *
   *	  It is also possible to match RowCompareExpr clauses to indexes (but
   *	  currently, only btree indexes handle this).  In this routine we will
   *	  report a match if the first column of the row comparison matches the
   *	  target index column.  This is sufficient to guarantee that some index
   *	  condition can be constructed from the RowCompareExpr --- whether the
   *	  remaining columns match the index too is considered in
   *	  adjust_rowcompare_for_index().
   *
   *	  It is also possible to match ScalarArrayOpExpr clauses to indexes, when
   *	  the clause is of the form "indexkey op ANY (arrayconst)".
   *
   *	  For boolean indexes, it is also possible to match the clause directly
   *	  to the indexkey; or perhaps the clause is (NOT indexkey).
   *
   * 'index' is the index of interest.
   * 'indexcol' is a column number of 'index' (counting from 0).
   * 'rinfo' is the clause to be tested (as a RestrictInfo node).
   *
   * Returns true if the clause can be used with this index key.
   *
   * NOTE:  returns false if clause is an OR or AND clause; it is the
   * responsibility of higher-level routines to cope with those.
   */
  static bool
  match_clause_to_indexcol(IndexOptInfo *index,
  						 int indexcol,
  						 RestrictInfo *rinfo)
  {
  	Expr	   *clause = rinfo->clause;
  	Index		index_relid = index->rel->relid;
  	Oid			opfamily = index->opfamily[indexcol];
  	Oid			idxcollation = index->indexcollations[indexcol];
  	Node	   *leftop,
  			   *rightop;
  	Relids		left_relids;
  	Relids		right_relids;
  	Oid			expr_op;
  	Oid			expr_coll;
  	bool		plain_op;
  
  	/*
  	 * Never match pseudoconstants to indexes.  (Normally this could not
  	 * happen anyway, since a pseudoconstant clause couldn't contain a Var,
  	 * but what if someone builds an expression index on a constant? It's not
  	 * totally unreasonable to do so with a partial index, either.)
  	 */
  	if (rinfo->pseudoconstant)
  		return false;
  
  	/* First check for boolean-index cases. */
  	if (IsBooleanOpfamily(opfamily))
  	{
  		if (match_boolean_index_clause((Node *) clause, indexcol, index))
  			return true;
  	}
  
  	/*
  	 * Clause must be a binary opclause, or possibly a ScalarArrayOpExpr
  	 * (which is always binary, by definition).  Or it could be a
  	 * RowCompareExpr, which we pass off to match_rowcompare_to_indexcol().
  	 * Or, if the index supports it, we can handle IS NULL/NOT NULL clauses.
  	 */
  	if (is_opclause(clause))
  	{
  		leftop = get_leftop(clause);
  		rightop = get_rightop(clause);
  		if (!leftop || !rightop)
  			return false;
  		left_relids = rinfo->left_relids;
  		right_relids = rinfo->right_relids;
  		expr_op = ((OpExpr *) clause)->opno;
  		expr_coll = ((OpExpr *) clause)->inputcollid;
  		plain_op = true;
  	}
  	else if (clause && IsA(clause, ScalarArrayOpExpr))
  	{
  		ScalarArrayOpExpr *saop = (ScalarArrayOpExpr *) clause;
  
  		/* We only accept ANY clauses, not ALL */
  		if (!saop->useOr)
  			return false;
  		leftop = (Node *) linitial(saop->args);
  		rightop = (Node *) lsecond(saop->args);
  		left_relids = NULL;		/* not actually needed */
  		right_relids = pull_varnos(rightop);
  		expr_op = saop->opno;
  		expr_coll = saop->inputcollid;
  		plain_op = false;
  	}
  	else if (clause && IsA(clause, RowCompareExpr))
  	{
  		return match_rowcompare_to_indexcol(index, indexcol,
  											opfamily, idxcollation,
  											(RowCompareExpr *) clause);
  	}
  	else if (index->amsearchnulls && IsA(clause, NullTest))
  	{
  		NullTest   *nt = (NullTest *) clause;
  
  		if (!nt->argisrow &&
  			match_index_to_operand((Node *) nt->arg, indexcol, index))
  			return true;
  		return false;
  	}
  	else
  		return false;
  
  	/*
  	 * Check for clauses of the form: (indexkey operator constant) or
  	 * (constant operator indexkey).  See above notes about const-ness.
  	 */
  	if (match_index_to_operand(leftop, indexcol, index) &&
  		!bms_is_member(index_relid, right_relids) &&
  		!contain_volatile_functions(rightop))
  	{
  		if (IndexCollMatchesExprColl(idxcollation, expr_coll) &&
  			is_indexable_operator(expr_op, opfamily, true))
  			return true;
  
  		/*
  		 * If we didn't find a member of the index's opfamily, see whether it
  		 * is a "special" indexable operator.
  		 */
  		if (plain_op &&
  			match_special_index_operator(clause, opfamily,
  										 idxcollation, true))
  			return true;
  		return false;
  	}
  
  	if (plain_op &&
  		match_index_to_operand(rightop, indexcol, index) &&
  		!bms_is_member(index_relid, left_relids) &&
  		!contain_volatile_functions(leftop))
  	{
  		if (IndexCollMatchesExprColl(idxcollation, expr_coll) &&
  			is_indexable_operator(expr_op, opfamily, false))
  			return true;
  
  		/*
  		 * If we didn't find a member of the index's opfamily, see whether it
  		 * is a "special" indexable operator.
  		 */
  		if (match_special_index_operator(clause, opfamily,
  										 idxcollation, false))
  			return true;
  		return false;
  	}
  
  	return false;
  }
  
  /*
   * is_indexable_operator
   *	  Does the operator match the specified index opfamily?
   *
   * If the indexkey is on the right, what we actually want to know
   * is whether the operator has a commutator operator that matches
   * the opfamily.
   */
  static bool
  is_indexable_operator(Oid expr_op, Oid opfamily, bool indexkey_on_left)
  {
  	/* Get the commuted operator if necessary */
  	if (!indexkey_on_left)
  	{
  		expr_op = get_commutator(expr_op);
  		if (expr_op == InvalidOid)
  			return false;
  	}
  
  	/* OK if the (commuted) operator is a member of the index's opfamily */
  	return op_in_opfamily(expr_op, opfamily);
  }
  
  /*
   * match_rowcompare_to_indexcol()
   *	  Handles the RowCompareExpr case for match_clause_to_indexcol(),
   *	  which see for comments.
   */
  static bool
  match_rowcompare_to_indexcol(IndexOptInfo *index,
  							 int indexcol,
  							 Oid opfamily,
  							 Oid idxcollation,
  							 RowCompareExpr *clause)
  {
  	Index		index_relid = index->rel->relid;
  	Node	   *leftop,
  			   *rightop;
  	Oid			expr_op;
  	Oid			expr_coll;
  
  	/* Forget it if we're not dealing with a btree index */
  	if (index->relam != BTREE_AM_OID)
  		return false;
  
  	/*
  	 * We could do the matching on the basis of insisting that the opfamily
  	 * shown in the RowCompareExpr be the same as the index column's opfamily,
  	 * but that could fail in the presence of reverse-sort opfamilies: it'd be
  	 * a matter of chance whether RowCompareExpr had picked the forward or
  	 * reverse-sort family.  So look only at the operator, and match if it is
  	 * a member of the index's opfamily (after commutation, if the indexkey is
  	 * on the right).  We'll worry later about whether any additional
  	 * operators are matchable to the index.
  	 */
  	leftop = (Node *) linitial(clause->largs);
  	rightop = (Node *) linitial(clause->rargs);
  	expr_op = linitial_oid(clause->opnos);
  	expr_coll = linitial_oid(clause->inputcollids);
  
  	/* Collations must match, if relevant */
  	if (!IndexCollMatchesExprColl(idxcollation, expr_coll))
  		return false;
  
  	/*
  	 * These syntactic tests are the same as in match_clause_to_indexcol()
  	 */
  	if (match_index_to_operand(leftop, indexcol, index) &&
  		!bms_is_member(index_relid, pull_varnos(rightop)) &&
  		!contain_volatile_functions(rightop))
  	{
  		/* OK, indexkey is on left */
  	}
  	else if (match_index_to_operand(rightop, indexcol, index) &&
  			 !bms_is_member(index_relid, pull_varnos(leftop)) &&
  			 !contain_volatile_functions(leftop))
  	{
  		/* indexkey is on right, so commute the operator */
  		expr_op = get_commutator(expr_op);
  		if (expr_op == InvalidOid)
  			return false;
  	}
  	else
  		return false;
  
  	/* We're good if the operator is the right type of opfamily member */
  	switch (get_op_opfamily_strategy(expr_op, opfamily))
  	{
  		case BTLessStrategyNumber:
  		case BTLessEqualStrategyNumber:
  		case BTGreaterEqualStrategyNumber:
  		case BTGreaterStrategyNumber:
  			return true;
  	}
  
  	return false;
  }
  
  
  /****************************************************************************
   *				----  ROUTINES TO CHECK ORDERING OPERATORS	----
   ****************************************************************************/
  
  /*
   * match_pathkeys_to_index
   *		Test whether an index can produce output ordered according to the
   *		given pathkeys using "ordering operators".
   *
   * If it can, return a list of suitable ORDER BY expressions, each of the form
   * "indexedcol operator pseudoconstant", along with an integer list of the
   * index column numbers (zero based) that each clause would be used with.
   * NIL lists are returned if the ordering is not achievable this way.
   *
   * On success, the result list is ordered by pathkeys, and in fact is
   * one-to-one with the requested pathkeys.
   */
  static void
  match_pathkeys_to_index(IndexOptInfo *index, List *pathkeys,
  						List **orderby_clauses_p,
  						List **clause_columns_p)
  {
  	List	   *orderby_clauses = NIL;
  	List	   *clause_columns = NIL;
  	ListCell   *lc1;
  
  	*orderby_clauses_p = NIL;	/* set default results */
  	*clause_columns_p = NIL;
  
  	/* Only indexes with the amcanorderbyop property are interesting here */
  	if (!index->amcanorderbyop)
  		return;
  
  	foreach(lc1, pathkeys)
  	{
  		PathKey    *pathkey = (PathKey *) lfirst(lc1);
  		bool		found = false;
  		ListCell   *lc2;
  
  		/*
  		 * Note: for any failure to match, we just return NIL immediately.
  		 * There is no value in matching just some of the pathkeys.
  		 */
  
  		/* Pathkey must request default sort order for the target opfamily */
  		if (pathkey->pk_strategy != BTLessStrategyNumber ||
  			pathkey->pk_nulls_first)
  			return;
  
  		/* If eclass is volatile, no hope of using an indexscan */
  		if (pathkey->pk_eclass->ec_has_volatile)
  			return;
  
  		/*
  		 * Try to match eclass member expression(s) to index.  Note that child
  		 * EC members are considered, but only when they belong to the target
  		 * relation.  (Unlike regular members, the same expression could be a
  		 * child member of more than one EC.  Therefore, the same index could
  		 * be considered to match more than one pathkey list, which is OK
  		 * here.  See also get_eclass_for_sort_expr.)
  		 */
  		foreach(lc2, pathkey->pk_eclass->ec_members)
  		{
  			EquivalenceMember *member = (EquivalenceMember *) lfirst(lc2);
  			int			indexcol;
  
  			/* No possibility of match if it references other relations */
  			if (!bms_equal(member->em_relids, index->rel->relids))
  				continue;
  
  			/*
  			 * We allow any column of the index to match each pathkey; they
  			 * don't have to match left-to-right as you might expect.  This is
  			 * correct for GiST, which is the sole existing AM supporting
  			 * amcanorderbyop.  We might need different logic in future for
  			 * other implementations.
  			 */
  			for (indexcol = 0; indexcol < index->ncolumns; indexcol++)
  			{
  				Expr	   *expr;
  
  				expr = match_clause_to_ordering_op(index,
  												   indexcol,
  												   member->em_expr,
  												   pathkey->pk_opfamily);
  				if (expr)
  				{
  					orderby_clauses = lappend(orderby_clauses, expr);
  					clause_columns = lappend_int(clause_columns, indexcol);
  					found = true;
  					break;
  				}
  			}
  
  			if (found)			/* don't want to look at remaining members */
  				break;
  		}
  
  		if (!found)				/* fail if no match for this pathkey */
  			return;
  	}
  
  	*orderby_clauses_p = orderby_clauses;		/* success! */
  	*clause_columns_p = clause_columns;
  }
  
  /*
   * match_clause_to_ordering_op
   *	  Determines whether an ordering operator expression matches an
   *	  index column.
   *
   *	  This is similar to, but simpler than, match_clause_to_indexcol.
   *	  We only care about simple OpExpr cases.  The input is a bare
   *	  expression that is being ordered by, which must be of the form
   *	  (indexkey op const) or (const op indexkey) where op is an ordering
   *	  operator for the column's opfamily.
   *
   * 'index' is the index of interest.
   * 'indexcol' is a column number of 'index' (counting from 0).
   * 'clause' is the ordering expression to be tested.
   * 'pk_opfamily' is the btree opfamily describing the required sort order.
   *
   * Note that we currently do not consider the collation of the ordering
   * operator's result.  In practical cases the result type will be numeric
   * and thus have no collation, and it's not very clear what to match to
   * if it did have a collation.  The index's collation should match the
   * ordering operator's input collation, not its result.
   *
   * If successful, return 'clause' as-is if the indexkey is on the left,
   * otherwise a commuted copy of 'clause'.  If no match, return NULL.
   */
  static Expr *
  match_clause_to_ordering_op(IndexOptInfo *index,
  							int indexcol,
  							Expr *clause,
  							Oid pk_opfamily)
  {
  	Oid			opfamily = index->opfamily[indexcol];
  	Oid			idxcollation = index->indexcollations[indexcol];
  	Node	   *leftop,
  			   *rightop;
  	Oid			expr_op;
  	Oid			expr_coll;
  	Oid			sortfamily;
  	bool		commuted;
  
  	/*
  	 * Clause must be a binary opclause.
  	 */
  	if (!is_opclause(clause))
  		return NULL;
  	leftop = get_leftop(clause);
  	rightop = get_rightop(clause);
  	if (!leftop || !rightop)
  		return NULL;
  	expr_op = ((OpExpr *) clause)->opno;
  	expr_coll = ((OpExpr *) clause)->inputcollid;
  
  	/*
  	 * We can forget the whole thing right away if wrong collation.
  	 */
  	if (!IndexCollMatchesExprColl(idxcollation, expr_coll))
  		return NULL;
  
  	/*
  	 * Check for clauses of the form: (indexkey operator constant) or
  	 * (constant operator indexkey).
  	 */
  	if (match_index_to_operand(leftop, indexcol, index) &&
  		!contain_var_clause(rightop) &&
  		!contain_volatile_functions(rightop))
  	{
  		commuted = false;
  	}
  	else if (match_index_to_operand(rightop, indexcol, index) &&
  			 !contain_var_clause(leftop) &&
  			 !contain_volatile_functions(leftop))
  	{
  		/* Might match, but we need a commuted operator */
  		expr_op = get_commutator(expr_op);
  		if (expr_op == InvalidOid)
  			return NULL;
  		commuted = true;
  	}
  	else
  		return NULL;
  
  	/*
  	 * Is the (commuted) operator an ordering operator for the opfamily? And
  	 * if so, does it yield the right sorting semantics?
  	 */
  	sortfamily = get_op_opfamily_sortfamily(expr_op, opfamily);
  	if (sortfamily != pk_opfamily)
  		return NULL;
  
  	/* We have a match.  Return clause or a commuted version thereof. */
  	if (commuted)
  	{
  		OpExpr	   *newclause = makeNode(OpExpr);
  
  		/* flat-copy all the fields of clause */
  		memcpy(newclause, clause, sizeof(OpExpr));
  
  		/* commute it */
  		newclause->opno = expr_op;
  		newclause->opfuncid = InvalidOid;
  		newclause->args = list_make2(rightop, leftop);
  
  		clause = (Expr *) newclause;
  	}
  
  	return clause;
  }
  
  
  /****************************************************************************
   *				----  ROUTINES TO DO PARTIAL INDEX PREDICATE TESTS	----
   ****************************************************************************/
  
  /*
   * check_index_predicates
   *		Set the predicate-derived IndexOptInfo fields for each index
   *		of the specified relation.
   *
   * predOK is set true if the index is partial and its predicate is satisfied
   * for this query, ie the query's WHERE clauses imply the predicate.
   *
   * indrestrictinfo is set to the relation's baserestrictinfo list less any
   * conditions that are implied by the index's predicate.  (Obviously, for a
   * non-partial index, this is the same as baserestrictinfo.)  Such conditions
   * can be dropped from the plan when using the index, in certain cases.
   *
   * At one time it was possible for this to get re-run after adding more
   * restrictions to the rel, thus possibly letting us prove more indexes OK.
   * That doesn't happen any more (at least not in the core code's usage),
   * but this code still supports it in case extensions want to mess with the
   * baserestrictinfo list.  We assume that adding more restrictions can't make
   * an index not predOK.  We must recompute indrestrictinfo each time, though,
   * to make sure any newly-added restrictions get into it if needed.
   */
  void
  check_index_predicates(PlannerInfo *root, RelOptInfo *rel)
  {
  	List	   *clauselist;
  	bool		have_partial;
  	bool		is_target_rel;
  	Relids		otherrels;
  	ListCell   *lc;
  
  	/*
  	 * Initialize the indrestrictinfo lists to be identical to
  	 * baserestrictinfo, and check whether there are any partial indexes.  If
  	 * not, this is all we need to do.
  	 */
  	have_partial = false;
  	foreach(lc, rel->indexlist)
  	{
  		IndexOptInfo *index = (IndexOptInfo *) lfirst(lc);
  
  		index->indrestrictinfo = rel->baserestrictinfo;
  		if (index->indpred)
  			have_partial = true;
  	}
  	if (!have_partial)
  		return;
  
  	/*
  	 * Construct a list of clauses that we can assume true for the purpose of
  	 * proving the index(es) usable.  Restriction clauses for the rel are
  	 * always usable, and so are any join clauses that are "movable to" this
  	 * rel.  Also, we can consider any EC-derivable join clauses (which must
  	 * be "movable to" this rel, by definition).
  	 */
  	clauselist = list_copy(rel->baserestrictinfo);
  
  	/* Scan the rel's join clauses */
  	foreach(lc, rel->joininfo)
  	{
  		RestrictInfo *rinfo = (RestrictInfo *) lfirst(lc);
  
  		/* Check if clause can be moved to this rel */
  		if (!join_clause_is_movable_to(rinfo, rel))
  			continue;
  
  		clauselist = lappend(clauselist, rinfo);
  	}
  
  	/*
  	 * Add on any equivalence-derivable join clauses.  Computing the correct
  	 * relid sets for generate_join_implied_equalities is slightly tricky
  	 * because the rel could be a child rel rather than a true baserel, and in
  	 * that case we must remove its parents' relid(s) from all_baserels.
  	 */
  	if (rel->reloptkind == RELOPT_OTHER_MEMBER_REL)
  		otherrels = bms_difference(root->all_baserels,
  								   find_childrel_parents(root, rel));
  	else
  		otherrels = bms_difference(root->all_baserels, rel->relids);
  
  	if (!bms_is_empty(otherrels))
  		clauselist =
  			list_concat(clauselist,
  						generate_join_implied_equalities(root,
  													   bms_union(rel->relids,
  																 otherrels),
  														 otherrels,
  														 rel));
  
  	/*
  	 * Normally we remove quals that are implied by a partial index's
  	 * predicate from indrestrictinfo, indicating that they need not be
  	 * checked explicitly by an indexscan plan using this index.  However, if
  	 * the rel is a target relation of UPDATE/DELETE/SELECT FOR UPDATE, we
  	 * cannot remove such quals from the plan, because they need to be in the
  	 * plan so that they will be properly rechecked by EvalPlanQual testing.
  	 * Some day we might want to remove such quals from the main plan anyway
  	 * and pass them through to EvalPlanQual via a side channel; but for now,
  	 * we just don't remove implied quals at all for target relations.
  	 */
  	is_target_rel = (rel->relid == root->parse->resultRelation ||
  					 get_plan_rowmark(root->rowMarks, rel->relid) != NULL);
  
  	/*
  	 * Now try to prove each index predicate true, and compute the
  	 * indrestrictinfo lists for partial indexes.  Note that we compute the
  	 * indrestrictinfo list even for non-predOK indexes; this might seem
  	 * wasteful, but we may be able to use such indexes in OR clauses, cf
  	 * generate_bitmap_or_paths().
  	 */
  	foreach(lc, rel->indexlist)
  	{
  		IndexOptInfo *index = (IndexOptInfo *) lfirst(lc);
  		ListCell   *lcr;
  
  		if (index->indpred == NIL)
  			continue;			/* ignore non-partial indexes here */
  
  		if (!index->predOK)		/* don't repeat work if already proven OK */
  			index->predOK = predicate_implied_by(index->indpred, clauselist);
  
  		/* If rel is an update target, leave indrestrictinfo as set above */
  		if (is_target_rel)
  			continue;
  
  		/* Else compute indrestrictinfo as the non-implied quals */
  		index->indrestrictinfo = NIL;
  		foreach(lcr, rel->baserestrictinfo)
  		{
  			RestrictInfo *rinfo = (RestrictInfo *) lfirst(lcr);
  
  			/* predicate_implied_by() assumes first arg is immutable */
  			if (contain_mutable_functions((Node *) rinfo->clause) ||
  				!predicate_implied_by(list_make1(rinfo->clause),
  									  index->indpred))
  				index->indrestrictinfo = lappend(index->indrestrictinfo, rinfo);
  		}
  	}
  }
  
  /****************************************************************************
   *				----  ROUTINES TO CHECK EXTERNALLY-VISIBLE CONDITIONS  ----
   ****************************************************************************/
  
  /*
   * ec_member_matches_indexcol
   *	  Test whether an EquivalenceClass member matches an index column.
   *
   * This is a callback for use by generate_implied_equalities_for_column.
   */
  static bool
  ec_member_matches_indexcol(PlannerInfo *root, RelOptInfo *rel,
  						   EquivalenceClass *ec, EquivalenceMember *em,
  						   void *arg)
  {
  	IndexOptInfo *index = ((ec_member_matches_arg *) arg)->index;
  	int			indexcol = ((ec_member_matches_arg *) arg)->indexcol;
  	Oid			curFamily = index->opfamily[indexcol];
  	Oid			curCollation = index->indexcollations[indexcol];
  
  	/*
  	 * If it's a btree index, we can reject it if its opfamily isn't
  	 * compatible with the EC, since no clause generated from the EC could be
  	 * used with the index.  For non-btree indexes, we can't easily tell
  	 * whether clauses generated from the EC could be used with the index, so
  	 * don't check the opfamily.  This might mean we return "true" for a
  	 * useless EC, so we have to recheck the results of
  	 * generate_implied_equalities_for_column; see
  	 * match_eclass_clauses_to_index.
  	 */
  	if (index->relam == BTREE_AM_OID &&
  		!list_member_oid(ec->ec_opfamilies, curFamily))
  		return false;
  
  	/* We insist on collation match for all index types, though */
  	if (!IndexCollMatchesExprColl(curCollation, ec->ec_collation))
  		return false;
  
  	return match_index_to_operand((Node *) em->em_expr, indexcol, index);
  }
  
  /*
   * relation_has_unique_index_for
   *	  Determine whether the relation provably has at most one row satisfying
   *	  a set of equality conditions, because the conditions constrain all
   *	  columns of some unique index.
   *
   * The conditions can be represented in either or both of two ways:
   * 1. A list of RestrictInfo nodes, where the caller has already determined
   * that each condition is a mergejoinable equality with an expression in
   * this relation on one side, and an expression not involving this relation
   * on the other.  The transient outer_is_left flag is used to identify which
   * side we should look at: left side if outer_is_left is false, right side
   * if it is true.
   * 2. A list of expressions in this relation, and a corresponding list of
   * equality operators. The caller must have already checked that the operators
   * represent equality.  (Note: the operators could be cross-type; the
   * expressions should correspond to their RHS inputs.)
   *
   * The caller need only supply equality conditions arising from joins;
   * this routine automatically adds in any usable baserestrictinfo clauses.
   * (Note that the passed-in restrictlist will be destructively modified!)
   */
  bool
  relation_has_unique_index_for(PlannerInfo *root, RelOptInfo *rel,
  							  List *restrictlist,
  							  List *exprlist, List *oprlist)
  {
  	ListCell   *ic;
  
  	Assert(list_length(exprlist) == list_length(oprlist));
  
  	/* Short-circuit if no indexes... */
  	if (rel->indexlist == NIL)
  		return false;
  
  	/*
  	 * Examine the rel's restriction clauses for usable var = const clauses
  	 * that we can add to the restrictlist.
  	 */
  	foreach(ic, rel->baserestrictinfo)
  	{
  		RestrictInfo *restrictinfo = (RestrictInfo *) lfirst(ic);
  
  		/*
  		 * Note: can_join won't be set for a restriction clause, but
  		 * mergeopfamilies will be if it has a mergejoinable operator and
  		 * doesn't contain volatile functions.
  		 */
  		if (restrictinfo->mergeopfamilies == NIL)
  			continue;			/* not mergejoinable */
  
  		/*
  		 * The clause certainly doesn't refer to anything but the given rel.
  		 * If either side is pseudoconstant then we can use it.
  		 */
  		if (bms_is_empty(restrictinfo->left_relids))
  		{
  			/* righthand side is inner */
  			restrictinfo->outer_is_left = true;
  		}
  		else if (bms_is_empty(restrictinfo->right_relids))
  		{
  			/* lefthand side is inner */
  			restrictinfo->outer_is_left = false;
  		}
  		else
  			continue;
  
  		/* OK, add to list */
  		restrictlist = lappend(restrictlist, restrictinfo);
  	}
  
  	/* Short-circuit the easy case */
  	if (restrictlist == NIL && exprlist == NIL)
  		return false;
  
  	/* Examine each index of the relation ... */
  	foreach(ic, rel->indexlist)
  	{
  		IndexOptInfo *ind = (IndexOptInfo *) lfirst(ic);
  		int			c;
  
  		/*
  		 * If the index is not unique, or not immediately enforced, or if it's
  		 * a partial index that doesn't match the query, it's useless here.
  		 */
  		if (!ind->unique || !ind->immediate ||
  			(ind->indpred != NIL && !ind->predOK))
  			continue;
  
  		/*
  		 * Try to find each index column in the lists of conditions.  This is
  		 * O(N^2) or worse, but we expect all the lists to be short.
  		 */
  		for (c = 0; c < ind->ncolumns; c++)
  		{
  			bool		matched = false;
  			ListCell   *lc;
  			ListCell   *lc2;
  
  			foreach(lc, restrictlist)
  			{
  				RestrictInfo *rinfo = (RestrictInfo *) lfirst(lc);
  				Node	   *rexpr;
  
  				/*
  				 * The condition's equality operator must be a member of the
  				 * index opfamily, else it is not asserting the right kind of
  				 * equality behavior for this index.  We check this first
  				 * since it's probably cheaper than match_index_to_operand().
  				 */
  				if (!list_member_oid(rinfo->mergeopfamilies, ind->opfamily[c]))
  					continue;
  
  				/*
  				 * XXX at some point we may need to check collations here too.
  				 * For the moment we assume all collations reduce to the same
  				 * notion of equality.
  				 */
  
  				/* OK, see if the condition operand matches the index key */
  				if (rinfo->outer_is_left)
  					rexpr = get_rightop(rinfo->clause);
  				else
  					rexpr = get_leftop(rinfo->clause);
  
  				if (match_index_to_operand(rexpr, c, ind))
  				{
  					matched = true;		/* column is unique */
  					break;
  				}
  			}
  
  			if (matched)
  				continue;
  
  			forboth(lc, exprlist, lc2, oprlist)
  			{
  				Node	   *expr = (Node *) lfirst(lc);
  				Oid			opr = lfirst_oid(lc2);
  
  				/* See if the expression matches the index key */
  				if (!match_index_to_operand(expr, c, ind))
  					continue;
  
  				/*
  				 * The equality operator must be a member of the index
  				 * opfamily, else it is not asserting the right kind of
  				 * equality behavior for this index.  We assume the caller
  				 * determined it is an equality operator, so we don't need to
  				 * check any more tightly than this.
  				 */
  				if (!op_in_opfamily(opr, ind->opfamily[c]))
  					continue;
  
  				/*
  				 * XXX at some point we may need to check collations here too.
  				 * For the moment we assume all collations reduce to the same
  				 * notion of equality.
  				 */
  
  				matched = true; /* column is unique */
  				break;
  			}
  
  			if (!matched)
  				break;			/* no match; this index doesn't help us */
  		}
  
  		/* Matched all columns of this index? */
  		if (c == ind->ncolumns)
  			return true;
  	}
  
  	return false;
  }
  
  
  /****************************************************************************
   *				----  ROUTINES TO CHECK OPERANDS  ----
   ****************************************************************************/
  
  /*
   * match_index_to_operand()
   *	  Generalized test for a match between an index's key
   *	  and the operand on one side of a restriction or join clause.
   *
   * operand: the nodetree to be compared to the index
   * indexcol: the column number of the index (counting from 0)
   * index: the index of interest
   *
   * Note that we aren't interested in collations here; the caller must check
   * for a collation match, if it's dealing with an operator where that matters.
   *
   * This is exported for use in selfuncs.c.
   */
  bool
  match_index_to_operand(Node *operand,
  					   int indexcol,
  					   IndexOptInfo *index)
  {
  	int			indkey;
  
  	/*
  	 * Ignore any RelabelType node above the operand.   This is needed to be
  	 * able to apply indexscanning in binary-compatible-operator cases. Note:
  	 * we can assume there is at most one RelabelType node;
  	 * eval_const_expressions() will have simplified if more than one.
  	 */
  	if (operand && IsA(operand, RelabelType))
  		operand = (Node *) ((RelabelType *) operand)->arg;
  
  	indkey = index->indexkeys[indexcol];
  	if (indkey != 0)
  	{
  		/*
  		 * Simple index column; operand must be a matching Var.
  		 */
  		if (operand && IsA(operand, Var) &&
  			index->rel->relid == ((Var *) operand)->varno &&
  			indkey == ((Var *) operand)->varattno)
  			return true;
  	}
  	else
  	{
  		/*
  		 * Index expression; find the correct expression.  (This search could
  		 * be avoided, at the cost of complicating all the callers of this
  		 * routine; doesn't seem worth it.)
  		 */
  		ListCell   *indexpr_item;
  		int			i;
  		Node	   *indexkey;
  
  		indexpr_item = list_head(index->indexprs);
  		for (i = 0; i < indexcol; i++)
  		{
  			if (index->indexkeys[i] == 0)
  			{
  				if (indexpr_item == NULL)
  					elog(ERROR, "wrong number of index expressions");
  				indexpr_item = lnext(indexpr_item);
  			}
  		}
  		if (indexpr_item == NULL)
  			elog(ERROR, "wrong number of index expressions");
  		indexkey = (Node *) lfirst(indexpr_item);
  
  		/*
  		 * Does it match the operand?  Again, strip any relabeling.
  		 */
  		if (indexkey && IsA(indexkey, RelabelType))
  			indexkey = (Node *) ((RelabelType *) indexkey)->arg;
  
  		if (equal(indexkey, operand))
  			return true;
  	}
  
  	return false;
  }
  
  /****************************************************************************
   *			----  ROUTINES FOR "SPECIAL" INDEXABLE OPERATORS  ----
   ****************************************************************************/
  
  /*
   * These routines handle special optimization of operators that can be
   * used with index scans even though they are not known to the executor's
   * indexscan machinery.  The key idea is that these operators allow us
   * to derive approximate indexscan qual clauses, such that any tuples
   * that pass the operator clause itself must also satisfy the simpler
   * indexscan condition(s).  Then we can use the indexscan machinery
   * to avoid scanning as much of the table as we'd otherwise have to,
   * while applying the original operator as a qpqual condition to ensure
   * we deliver only the tuples we want.  (In essence, we're using a regular
   * index as if it were a lossy index.)
   *
   * An example of what we're doing is
   *			textfield LIKE 'abc%'
   * from which we can generate the indexscanable conditions
   *			textfield >= 'abc' AND textfield < 'abd'
   * which allow efficient scanning of an index on textfield.
   * (In reality, character set and collation issues make the transformation
   * from LIKE to indexscan limits rather harder than one might think ...
   * but that's the basic idea.)
   *
   * Another thing that we do with this machinery is to provide special
   * smarts for "boolean" indexes (that is, indexes on boolean columns
   * that support boolean equality).  We can transform a plain reference
   * to the indexkey into "indexkey = true", or "NOT indexkey" into
   * "indexkey = false", so as to make the expression indexable using the
   * regular index operators.  (As of Postgres 8.1, we must do this here
   * because constant simplification does the reverse transformation;
   * without this code there'd be no way to use such an index at all.)
   *
   * Three routines are provided here:
   *
   * match_special_index_operator() is just an auxiliary function for
   * match_clause_to_indexcol(); after the latter fails to recognize a
   * restriction opclause's operator as a member of an index's opfamily,
   * it asks match_special_index_operator() whether the clause should be
   * considered an indexqual anyway.
   *
   * match_boolean_index_clause() similarly detects clauses that can be
   * converted into boolean equality operators.
   *
   * expand_indexqual_conditions() converts a list of RestrictInfo nodes
   * (with implicit AND semantics across list elements) into a list of clauses
   * that the executor can actually handle.  For operators that are members of
   * the index's opfamily this transformation is a no-op, but clauses recognized
   * by match_special_index_operator() or match_boolean_index_clause() must be
   * converted into one or more "regular" indexqual conditions.
   */
  
  /*
   * match_boolean_index_clause
   *	  Recognize restriction clauses that can be matched to a boolean index.
   *
   * This should be called only when IsBooleanOpfamily() recognizes the
   * index's operator family.  We check to see if the clause matches the
   * index's key.
   */
  static bool
  match_boolean_index_clause(Node *clause,
  						   int indexcol,
  						   IndexOptInfo *index)
  {
  	/* Direct match? */
  	if (match_index_to_operand(clause, indexcol, index))
  		return true;
  	/* NOT clause? */
  	if (not_clause(clause))
  	{
  		if (match_index_to_operand((Node *) get_notclausearg((Expr *) clause),
  								   indexcol, index))
  			return true;
  	}
  
  	/*
  	 * Since we only consider clauses at top level of WHERE, we can convert
  	 * indexkey IS TRUE and indexkey IS FALSE to index searches as well. The
  	 * different meaning for NULL isn't important.
  	 */
  	else if (clause && IsA(clause, BooleanTest))
  	{
  		BooleanTest *btest = (BooleanTest *) clause;
  
  		if (btest->booltesttype == IS_TRUE ||
  			btest->booltesttype == IS_FALSE)
  			if (match_index_to_operand((Node *) btest->arg,
  									   indexcol, index))
  				return true;
  	}
  	return false;
  }
  
  /*
   * match_special_index_operator
   *	  Recognize restriction clauses that can be used to generate
   *	  additional indexscanable qualifications.
   *
   * The given clause is already known to be a binary opclause having
   * the form (indexkey OP pseudoconst) or (pseudoconst OP indexkey),
   * but the OP proved not to be one of the index's opfamily operators.
   * Return 'true' if we can do something with it anyway.
   */
  static bool
  match_special_index_operator(Expr *clause, Oid opfamily, Oid idxcollation,
  							 bool indexkey_on_left)
  {
  	bool		isIndexable = false;
  	Node	   *rightop;
  	Oid			expr_op;
  	Oid			expr_coll;
  	Const	   *patt;
  	Const	   *prefix = NULL;
  	Pattern_Prefix_Status pstatus = Pattern_Prefix_None;
  
  	/*
  	 * Currently, all known special operators require the indexkey on the
  	 * left, but this test could be pushed into the switch statement if some
  	 * are added that do not...
  	 */
  	if (!indexkey_on_left)
  		return false;
  
  	/* we know these will succeed */
  	rightop = get_rightop(clause);
  	expr_op = ((OpExpr *) clause)->opno;
  	expr_coll = ((OpExpr *) clause)->inputcollid;
  
  	/* again, required for all current special ops: */
  	if (!IsA(rightop, Const) ||
  		((Const *) rightop)->constisnull)
  		return false;
  	patt = (Const *) rightop;
  
  	switch (expr_op)
  	{
  		case OID_TEXT_LIKE_OP:
  		case OID_BPCHAR_LIKE_OP:
  		case OID_NAME_LIKE_OP:
  			/* the right-hand const is type text for all of these */
  			pstatus = pattern_fixed_prefix(patt, Pattern_Type_Like, expr_coll,
  										   &prefix, NULL);
  			isIndexable = (pstatus != Pattern_Prefix_None);
  			break;
  
  		case OID_BYTEA_LIKE_OP:
  			pstatus = pattern_fixed_prefix(patt, Pattern_Type_Like, expr_coll,
  										   &prefix, NULL);
  			isIndexable = (pstatus != Pattern_Prefix_None);
  			break;
  
  		case OID_TEXT_ICLIKE_OP:
  		case OID_BPCHAR_ICLIKE_OP:
  		case OID_NAME_ICLIKE_OP:
  			/* the right-hand const is type text for all of these */
  			pstatus = pattern_fixed_prefix(patt, Pattern_Type_Like_IC, expr_coll,
  										   &prefix, NULL);
  			isIndexable = (pstatus != Pattern_Prefix_None);
  			break;
  
  		case OID_TEXT_REGEXEQ_OP:
  		case OID_BPCHAR_REGEXEQ_OP:
  		case OID_NAME_REGEXEQ_OP:
  			/* the right-hand const is type text for all of these */
  			pstatus = pattern_fixed_prefix(patt, Pattern_Type_Regex, expr_coll,
  										   &prefix, NULL);
  			isIndexable = (pstatus != Pattern_Prefix_None);
  			break;
  
  		case OID_TEXT_ICREGEXEQ_OP:
  		case OID_BPCHAR_ICREGEXEQ_OP:
  		case OID_NAME_ICREGEXEQ_OP:
  			/* the right-hand const is type text for all of these */
  			pstatus = pattern_fixed_prefix(patt, Pattern_Type_Regex_IC, expr_coll,
  										   &prefix, NULL);
  			isIndexable = (pstatus != Pattern_Prefix_None);
  			break;
  
  		case OID_INET_SUB_OP:
  		case OID_INET_SUBEQ_OP:
  			isIndexable = true;
  			break;
  	}
  
  	if (prefix)
  	{
  		pfree(DatumGetPointer(prefix->constvalue));
  		pfree(prefix);
  	}
  
  	/* done if the expression doesn't look indexable */
  	if (!isIndexable)
  		return false;
  
  	/*
  	 * Must also check that index's opfamily supports the operators we will
  	 * want to apply.  (A hash index, for example, will not support ">=".)
  	 * Currently, only btree and spgist support the operators we need.
  	 *
  	 * Note: actually, in the Pattern_Prefix_Exact case, we only need "=" so a
  	 * hash index would work.  Currently it doesn't seem worth checking for
  	 * that, however.
  	 *
  	 * We insist on the opfamily being the specific one we expect, else we'd
  	 * do the wrong thing if someone were to make a reverse-sort opfamily with
  	 * the same operators.
  	 *
  	 * The non-pattern opclasses will not sort the way we need in most non-C
  	 * locales.  We can use such an index anyway for an exact match (simple
  	 * equality), but not for prefix-match cases.  Note that here we are
  	 * looking at the index's collation, not the expression's collation --
  	 * this test is *not* dependent on the LIKE/regex operator's collation.
  	 */
  	switch (expr_op)
  	{
  		case OID_TEXT_LIKE_OP:
  		case OID_TEXT_ICLIKE_OP:
  		case OID_TEXT_REGEXEQ_OP:
  		case OID_TEXT_ICREGEXEQ_OP:
  			isIndexable =
  				(opfamily == TEXT_PATTERN_BTREE_FAM_OID) ||
  				(opfamily == TEXT_SPGIST_FAM_OID) ||
  				(opfamily == TEXT_BTREE_FAM_OID &&
  				 (pstatus == Pattern_Prefix_Exact ||
  				  lc_collate_is_c(idxcollation)));
  			break;
  
  		case OID_BPCHAR_LIKE_OP:
  		case OID_BPCHAR_ICLIKE_OP:
  		case OID_BPCHAR_REGEXEQ_OP:
  		case OID_BPCHAR_ICREGEXEQ_OP:
  			isIndexable =
  				(opfamily == BPCHAR_PATTERN_BTREE_FAM_OID) ||
  				(opfamily == BPCHAR_BTREE_FAM_OID &&
  				 (pstatus == Pattern_Prefix_Exact ||
  				  lc_collate_is_c(idxcollation)));
  			break;
  
  		case OID_NAME_LIKE_OP:
  		case OID_NAME_ICLIKE_OP:
  		case OID_NAME_REGEXEQ_OP:
  		case OID_NAME_ICREGEXEQ_OP:
  			/* name uses locale-insensitive sorting */
  			isIndexable = (opfamily == NAME_BTREE_FAM_OID);
  			break;
  
  		case OID_BYTEA_LIKE_OP:
  			isIndexable = (opfamily == BYTEA_BTREE_FAM_OID);
  			break;
  
  		case OID_INET_SUB_OP:
  		case OID_INET_SUBEQ_OP:
  			isIndexable = (opfamily == NETWORK_BTREE_FAM_OID);
  			break;
  	}
  
  	return isIndexable;
  }
  
  /*
   * expand_indexqual_conditions
   *	  Given a list of RestrictInfo nodes, produce a list of directly usable
   *	  index qual clauses.
   *
   * Standard qual clauses (those in the index's opfamily) are passed through
   * unchanged.  Boolean clauses and "special" index operators are expanded
   * into clauses that the indexscan machinery will know what to do with.
   * RowCompare clauses are simplified if necessary to create a clause that is
   * fully checkable by the index.
   *
   * In addition to the expressions themselves, there are auxiliary lists
   * of the index column numbers that the clauses are meant to be used with;
   * we generate an updated column number list for the result.  (This is not
   * the identical list because one input clause sometimes produces more than
   * one output clause.)
   *
   * The input clauses are sorted by column number, and so the output is too.
   * (This is depended on in various places in both planner and executor.)
   */
  void
  expand_indexqual_conditions(IndexOptInfo *index,
  							List *indexclauses, List *indexclausecols,
  							List **indexquals_p, List **indexqualcols_p)
  {
  	List	   *indexquals = NIL;
  	List	   *indexqualcols = NIL;
  	ListCell   *lcc,
  			   *lci;
  
  	forboth(lcc, indexclauses, lci, indexclausecols)
  	{
  		RestrictInfo *rinfo = (RestrictInfo *) lfirst(lcc);
  		int			indexcol = lfirst_int(lci);
  		Expr	   *clause = rinfo->clause;
  		Oid			curFamily = index->opfamily[indexcol];
  		Oid			curCollation = index->indexcollations[indexcol];
  
  		/* First check for boolean cases */
  		if (IsBooleanOpfamily(curFamily))
  		{
  			Expr	   *boolqual;
  
  			boolqual = expand_boolean_index_clause((Node *) clause,
  												   indexcol,
  												   index);
  			if (boolqual)
  			{
  				indexquals = lappend(indexquals,
  									 make_simple_restrictinfo(boolqual));
  				indexqualcols = lappend_int(indexqualcols, indexcol);
  				continue;
  			}
  		}
  
  		/*
  		 * Else it must be an opclause (usual case), ScalarArrayOp,
  		 * RowCompare, or NullTest
  		 */
  		if (is_opclause(clause))
  		{
  			indexquals = list_concat(indexquals,
  									 expand_indexqual_opclause(rinfo,
  															   curFamily,
  															   curCollation));
  			/* expand_indexqual_opclause can produce multiple clauses */
  			while (list_length(indexqualcols) < list_length(indexquals))
  				indexqualcols = lappend_int(indexqualcols, indexcol);
  		}
  		else if (IsA(clause, ScalarArrayOpExpr))
  		{
  			/* no extra work at this time */
  			indexquals = lappend(indexquals, rinfo);
  			indexqualcols = lappend_int(indexqualcols, indexcol);
  		}
  		else if (IsA(clause, RowCompareExpr))
  		{
  			indexquals = lappend(indexquals,
  								 expand_indexqual_rowcompare(rinfo,
  															 index,
  															 indexcol));
  			indexqualcols = lappend_int(indexqualcols, indexcol);
  		}
  		else if (IsA(clause, NullTest))
  		{
  			Assert(index->amsearchnulls);
  			indexquals = lappend(indexquals, rinfo);
  			indexqualcols = lappend_int(indexqualcols, indexcol);
  		}
  		else
  			elog(ERROR, "unsupported indexqual type: %d",
  				 (int) nodeTag(clause));
  	}
  
  	*indexquals_p = indexquals;
  	*indexqualcols_p = indexqualcols;
  }
  
  /*
   * expand_boolean_index_clause
   *	  Convert a clause recognized by match_boolean_index_clause into
   *	  a boolean equality operator clause.
   *
   * Returns NULL if the clause isn't a boolean index qual.
   */
  static Expr *
  expand_boolean_index_clause(Node *clause,
  							int indexcol,
  							IndexOptInfo *index)
  {
  	/* Direct match? */
  	if (match_index_to_operand(clause, indexcol, index))
  	{
  		/* convert to indexkey = TRUE */
  		return make_opclause(BooleanEqualOperator, BOOLOID, false,
  							 (Expr *) clause,
  							 (Expr *) makeBoolConst(true, false),
  							 InvalidOid, InvalidOid);
  	}
  	/* NOT clause? */
  	if (not_clause(clause))
  	{
  		Node	   *arg = (Node *) get_notclausearg((Expr *) clause);
  
  		/* It must have matched the indexkey */
  		Assert(match_index_to_operand(arg, indexcol, index));
  		/* convert to indexkey = FALSE */
  		return make_opclause(BooleanEqualOperator, BOOLOID, false,
  							 (Expr *) arg,
  							 (Expr *) makeBoolConst(false, false),
  							 InvalidOid, InvalidOid);
  	}
  	if (clause && IsA(clause, BooleanTest))
  	{
  		BooleanTest *btest = (BooleanTest *) clause;
  		Node	   *arg = (Node *) btest->arg;
  
  		/* It must have matched the indexkey */
  		Assert(match_index_to_operand(arg, indexcol, index));
  		if (btest->booltesttype == IS_TRUE)
  		{
  			/* convert to indexkey = TRUE */
  			return make_opclause(BooleanEqualOperator, BOOLOID, false,
  								 (Expr *) arg,
  								 (Expr *) makeBoolConst(true, false),
  								 InvalidOid, InvalidOid);
  		}
  		if (btest->booltesttype == IS_FALSE)
  		{
  			/* convert to indexkey = FALSE */
  			return make_opclause(BooleanEqualOperator, BOOLOID, false,
  								 (Expr *) arg,
  								 (Expr *) makeBoolConst(false, false),
  								 InvalidOid, InvalidOid);
  		}
  		/* Oops */
  		Assert(false);
  	}
  
  	return NULL;
  }
  
  /*
   * expand_indexqual_opclause --- expand a single indexqual condition
   *		that is an operator clause
   *
   * The input is a single RestrictInfo, the output a list of RestrictInfos.
   *
   * In the base case this is just list_make1(), but we have to be prepared to
   * expand special cases that were accepted by match_special_index_operator().
   */
  static List *
  expand_indexqual_opclause(RestrictInfo *rinfo, Oid opfamily, Oid idxcollation)
  {
  	Expr	   *clause = rinfo->clause;
  
  	/* we know these will succeed */
  	Node	   *leftop = get_leftop(clause);
  	Node	   *rightop = get_rightop(clause);
  	Oid			expr_op = ((OpExpr *) clause)->opno;
  	Oid			expr_coll = ((OpExpr *) clause)->inputcollid;
  	Const	   *patt = (Const *) rightop;
  	Const	   *prefix = NULL;
  	Pattern_Prefix_Status pstatus;
  
  	/*
  	 * LIKE and regex operators are not members of any btree index opfamily,
  	 * but they can be members of opfamilies for more exotic index types such
  	 * as GIN.  Therefore, we should only do expansion if the operator is
  	 * actually not in the opfamily.  But checking that requires a syscache
  	 * lookup, so it's best to first see if the operator is one we are
  	 * interested in.
  	 */
  	switch (expr_op)
  	{
  		case OID_TEXT_LIKE_OP:
  		case OID_BPCHAR_LIKE_OP:
  		case OID_NAME_LIKE_OP:
  		case OID_BYTEA_LIKE_OP:
  			if (!op_in_opfamily(expr_op, opfamily))
  			{
  				pstatus = pattern_fixed_prefix(patt, Pattern_Type_Like, expr_coll,
  											   &prefix, NULL);
  				return prefix_quals(leftop, opfamily, idxcollation, prefix, pstatus);
  			}
  			break;
  
  		case OID_TEXT_ICLIKE_OP:
  		case OID_BPCHAR_ICLIKE_OP:
  		case OID_NAME_ICLIKE_OP:
  			if (!op_in_opfamily(expr_op, opfamily))
  			{
  				/* the right-hand const is type text for all of these */
  				pstatus = pattern_fixed_prefix(patt, Pattern_Type_Like_IC, expr_coll,
  											   &prefix, NULL);
  				return prefix_quals(leftop, opfamily, idxcollation, prefix, pstatus);
  			}
  			break;
  
  		case OID_TEXT_REGEXEQ_OP:
  		case OID_BPCHAR_REGEXEQ_OP:
  		case OID_NAME_REGEXEQ_OP:
  			if (!op_in_opfamily(expr_op, opfamily))
  			{
  				/* the right-hand const is type text for all of these */
  				pstatus = pattern_fixed_prefix(patt, Pattern_Type_Regex, expr_coll,
  											   &prefix, NULL);
  				return prefix_quals(leftop, opfamily, idxcollation, prefix, pstatus);
  			}
  			break;
  
  		case OID_TEXT_ICREGEXEQ_OP:
  		case OID_BPCHAR_ICREGEXEQ_OP:
  		case OID_NAME_ICREGEXEQ_OP:
  			if (!op_in_opfamily(expr_op, opfamily))
  			{
  				/* the right-hand const is type text for all of these */
  				pstatus = pattern_fixed_prefix(patt, Pattern_Type_Regex_IC, expr_coll,
  											   &prefix, NULL);
  				return prefix_quals(leftop, opfamily, idxcollation, prefix, pstatus);
  			}
  			break;
  
  		case OID_INET_SUB_OP:
  		case OID_INET_SUBEQ_OP:
  			if (!op_in_opfamily(expr_op, opfamily))
  			{
  				return network_prefix_quals(leftop, expr_op, opfamily,
  											patt->constvalue);
  			}
  			break;
  	}
  
  	/* Default case: just make a list of the unmodified indexqual */
  	return list_make1(rinfo);
  }
  
  /*
   * expand_indexqual_rowcompare --- expand a single indexqual condition
   *		that is a RowCompareExpr
   *
   * This is a thin wrapper around adjust_rowcompare_for_index; we export the
   * latter so that createplan.c can use it to re-discover which columns of the
   * index are used by a row comparison indexqual.
   */
  static RestrictInfo *
  expand_indexqual_rowcompare(RestrictInfo *rinfo,
  							IndexOptInfo *index,
  							int indexcol)
  {
  	RowCompareExpr *clause = (RowCompareExpr *) rinfo->clause;
  	Expr	   *newclause;
  	List	   *indexcolnos;
  	bool		var_on_left;
  
  	newclause = adjust_rowcompare_for_index(clause,
  											index,
  											indexcol,
  											&indexcolnos,
  											&var_on_left);
  
  	/*
  	 * If we didn't have to change the RowCompareExpr, return the original
  	 * RestrictInfo.
  	 */
  	if (newclause == (Expr *) clause)
  		return rinfo;
  
  	/* Else we need a new RestrictInfo */
  	return make_simple_restrictinfo(newclause);
  }
  
  /*
   * adjust_rowcompare_for_index --- expand a single indexqual condition
   *		that is a RowCompareExpr
   *
   * It's already known that the first column of the row comparison matches
   * the specified column of the index.  We can use additional columns of the
   * row comparison as index qualifications, so long as they match the index
   * in the "same direction", ie, the indexkeys are all on the same side of the
   * clause and the operators are all the same-type members of the opfamilies.
   * If all the columns of the RowCompareExpr match in this way, we just use it
   * as-is.  Otherwise, we build a shortened RowCompareExpr (if more than one
   * column matches) or a simple OpExpr (if the first-column match is all
   * there is).  In these cases the modified clause is always "<=" or ">="
   * even when the original was "<" or ">" --- this is necessary to match all
   * the rows that could match the original.  (We are essentially building a
   * lossy version of the row comparison when we do this.)
   *
   * *indexcolnos receives an integer list of the index column numbers (zero
   * based) used in the resulting expression.  The reason we need to return
   * that is that if the index is selected for use, createplan.c will need to
   * call this again to extract that list.  (This is a bit grotty, but row
   * comparison indexquals aren't used enough to justify finding someplace to
   * keep the information in the Path representation.)  Since createplan.c
   * also needs to know which side of the RowCompareExpr is the index side,
   * we also return *var_on_left_p rather than re-deducing that there.
   */
  Expr *
  adjust_rowcompare_for_index(RowCompareExpr *clause,
  							IndexOptInfo *index,
  							int indexcol,
  							List **indexcolnos,
  							bool *var_on_left_p)
  {
  	bool		var_on_left;
  	int			op_strategy;
  	Oid			op_lefttype;
  	Oid			op_righttype;
  	int			matching_cols;
  	Oid			expr_op;
  	List	   *opfamilies;
  	List	   *lefttypes;
  	List	   *righttypes;
  	List	   *new_ops;
  	ListCell   *largs_cell;
  	ListCell   *rargs_cell;
  	ListCell   *opnos_cell;
  	ListCell   *collids_cell;
  
  	/* We have to figure out (again) how the first col matches */
  	var_on_left = match_index_to_operand((Node *) linitial(clause->largs),
  										 indexcol, index);
  	Assert(var_on_left ||
  		   match_index_to_operand((Node *) linitial(clause->rargs),
  								  indexcol, index));
  	*var_on_left_p = var_on_left;
  
  	expr_op = linitial_oid(clause->opnos);
  	if (!var_on_left)
  		expr_op = get_commutator(expr_op);
  	get_op_opfamily_properties(expr_op, index->opfamily[indexcol], false,
  							   &op_strategy,
  							   &op_lefttype,
  							   &op_righttype);
  
  	/* Initialize returned list of which index columns are used */
  	*indexcolnos = list_make1_int(indexcol);
  
  	/* Build lists of the opfamilies and operator datatypes in case needed */
  	opfamilies = list_make1_oid(index->opfamily[indexcol]);
  	lefttypes = list_make1_oid(op_lefttype);
  	righttypes = list_make1_oid(op_righttype);
  
  	/*
  	 * See how many of the remaining columns match some index column in the
  	 * same way.  As in match_clause_to_indexcol(), the "other" side of any
  	 * potential index condition is OK as long as it doesn't use Vars from the
  	 * indexed relation.
  	 */
  	matching_cols = 1;
  	largs_cell = lnext(list_head(clause->largs));
  	rargs_cell = lnext(list_head(clause->rargs));
  	opnos_cell = lnext(list_head(clause->opnos));
  	collids_cell = lnext(list_head(clause->inputcollids));
  
  	while (largs_cell != NULL)
  	{
  		Node	   *varop;
  		Node	   *constop;
  		int			i;
  
  		expr_op = lfirst_oid(opnos_cell);
  		if (var_on_left)
  		{
  			varop = (Node *) lfirst(largs_cell);
  			constop = (Node *) lfirst(rargs_cell);
  		}
  		else
  		{
  			varop = (Node *) lfirst(rargs_cell);
  			constop = (Node *) lfirst(largs_cell);
  			/* indexkey is on right, so commute the operator */
  			expr_op = get_commutator(expr_op);
  			if (expr_op == InvalidOid)
  				break;			/* operator is not usable */
  		}
  		if (bms_is_member(index->rel->relid, pull_varnos(constop)))
  			break;				/* no good, Var on wrong side */
  		if (contain_volatile_functions(constop))
  			break;				/* no good, volatile comparison value */
  
  		/*
  		 * The Var side can match any column of the index.
  		 */
  		for (i = 0; i < index->ncolumns; i++)
  		{
  			if (match_index_to_operand(varop, i, index) &&
  				get_op_opfamily_strategy(expr_op,
  										 index->opfamily[i]) == op_strategy &&
  				IndexCollMatchesExprColl(index->indexcollations[i],
  										 lfirst_oid(collids_cell)))
  				break;
  		}
  		if (i >= index->ncolumns)
  			break;				/* no match found */
  
  		/* Add column number to returned list */
  		*indexcolnos = lappend_int(*indexcolnos, i);
  
  		/* Add opfamily and datatypes to lists */
  		get_op_opfamily_properties(expr_op, index->opfamily[i], false,
  								   &op_strategy,
  								   &op_lefttype,
  								   &op_righttype);
  		opfamilies = lappend_oid(opfamilies, index->opfamily[i]);
  		lefttypes = lappend_oid(lefttypes, op_lefttype);
  		righttypes = lappend_oid(righttypes, op_righttype);
  
  		/* This column matches, keep scanning */
  		matching_cols++;
  		largs_cell = lnext(largs_cell);
  		rargs_cell = lnext(rargs_cell);
  		opnos_cell = lnext(opnos_cell);
  		collids_cell = lnext(collids_cell);
  	}
  
  	/* Return clause as-is if it's all usable as index quals */
  	if (matching_cols == list_length(clause->opnos))
  		return (Expr *) clause;
  
  	/*
  	 * We have to generate a subset rowcompare (possibly just one OpExpr). The
  	 * painful part of this is changing < to <= or > to >=, so deal with that
  	 * first.
  	 */
  	if (op_strategy == BTLessEqualStrategyNumber ||
  		op_strategy == BTGreaterEqualStrategyNumber)
  	{
  		/* easy, just use the same operators */
  		new_ops = list_truncate(list_copy(clause->opnos), matching_cols);
  	}
  	else
  	{
  		ListCell   *opfamilies_cell;
  		ListCell   *lefttypes_cell;
  		ListCell   *righttypes_cell;
  
  		if (op_strategy == BTLessStrategyNumber)
  			op_strategy = BTLessEqualStrategyNumber;
  		else if (op_strategy == BTGreaterStrategyNumber)
  			op_strategy = BTGreaterEqualStrategyNumber;
  		else
  			elog(ERROR, "unexpected strategy number %d", op_strategy);
  		new_ops = NIL;
  		lefttypes_cell = list_head(lefttypes);
  		righttypes_cell = list_head(righttypes);
  		foreach(opfamilies_cell, opfamilies)
  		{
  			Oid			opfam = lfirst_oid(opfamilies_cell);
  			Oid			lefttype = lfirst_oid(lefttypes_cell);
  			Oid			righttype = lfirst_oid(righttypes_cell);
  
  			expr_op = get_opfamily_member(opfam, lefttype, righttype,
  										  op_strategy);
  			if (!OidIsValid(expr_op))	/* should not happen */
  				elog(ERROR, "could not find member %d(%u,%u) of opfamily %u",
  					 op_strategy, lefttype, righttype, opfam);
  			if (!var_on_left)
  			{
  				expr_op = get_commutator(expr_op);
  				if (!OidIsValid(expr_op))		/* should not happen */
  					elog(ERROR, "could not find commutator of member %d(%u,%u) of opfamily %u",
  						 op_strategy, lefttype, righttype, opfam);
  			}
  			new_ops = lappend_oid(new_ops, expr_op);
  			lefttypes_cell = lnext(lefttypes_cell);
  			righttypes_cell = lnext(righttypes_cell);
  		}
  	}
  
  	/* If we have more than one matching col, create a subset rowcompare */
  	if (matching_cols > 1)
  	{
  		RowCompareExpr *rc = makeNode(RowCompareExpr);
  
  		if (var_on_left)
  			rc->rctype = (RowCompareType) op_strategy;
  		else
  			rc->rctype = (op_strategy == BTLessEqualStrategyNumber) ?
  				ROWCOMPARE_GE : ROWCOMPARE_LE;
  		rc->opnos = new_ops;
  		rc->opfamilies = list_truncate(list_copy(clause->opfamilies),
  									   matching_cols);
  		rc->inputcollids = list_truncate(list_copy(clause->inputcollids),
  										 matching_cols);
  		rc->largs = list_truncate((List *) copyObject(clause->largs),
  								  matching_cols);
  		rc->rargs = list_truncate((List *) copyObject(clause->rargs),
  								  matching_cols);
  		return (Expr *) rc;
  	}
  	else
  	{
  		return make_opclause(linitial_oid(new_ops), BOOLOID, false,
  							 copyObject(linitial(clause->largs)),
  							 copyObject(linitial(clause->rargs)),
  							 InvalidOid,
  							 linitial_oid(clause->inputcollids));
  	}
  }
  
  /*
   * Given a fixed prefix that all the "leftop" values must have,
   * generate suitable indexqual condition(s).  opfamily is the index
   * operator family; we use it to deduce the appropriate comparison
   * operators and operand datatypes.  collation is the input collation to use.
   */
  static List *
  prefix_quals(Node *leftop, Oid opfamily, Oid collation,
  			 Const *prefix_const, Pattern_Prefix_Status pstatus)
  {
  	List	   *result;
  	Oid			datatype;
  	Oid			oproid;
  	Expr	   *expr;
  	FmgrInfo	ltproc;
  	Const	   *greaterstr;
  
  	Assert(pstatus != Pattern_Prefix_None);
  
  	switch (opfamily)
  	{
  		case TEXT_BTREE_FAM_OID:
  		case TEXT_PATTERN_BTREE_FAM_OID:
  		case TEXT_SPGIST_FAM_OID:
  			datatype = TEXTOID;
  			break;
  
  		case BPCHAR_BTREE_FAM_OID:
  		case BPCHAR_PATTERN_BTREE_FAM_OID:
  			datatype = BPCHAROID;
  			break;
  
  		case NAME_BTREE_FAM_OID:
  			datatype = NAMEOID;
  			break;
  
  		case BYTEA_BTREE_FAM_OID:
  			datatype = BYTEAOID;
  			break;
  
  		default:
  			/* shouldn't get here */
  			elog(ERROR, "unexpected opfamily: %u", opfamily);
  			return NIL;
  	}
  
  	/*
  	 * If necessary, coerce the prefix constant to the right type. The given
  	 * prefix constant is either text or bytea type.
  	 */
  	if (prefix_const->consttype != datatype)
  	{
  		char	   *prefix;
  
  		switch (prefix_const->consttype)
  		{
  			case TEXTOID:
  				prefix = TextDatumGetCString(prefix_const->constvalue);
  				break;
  			case BYTEAOID:
  				prefix = DatumGetCString(DirectFunctionCall1(byteaout,
  												  prefix_const->constvalue));
  				break;
  			default:
  				elog(ERROR, "unexpected const type: %u",
  					 prefix_const->consttype);
  				return NIL;
  		}
  		prefix_const = string_to_const(prefix, datatype);
  		pfree(prefix);
  	}
  
  	/*
  	 * If we found an exact-match pattern, generate an "=" indexqual.
  	 */
  	if (pstatus == Pattern_Prefix_Exact)
  	{
  		oproid = get_opfamily_member(opfamily, datatype, datatype,
  									 BTEqualStrategyNumber);
  		if (oproid == InvalidOid)
  			elog(ERROR, "no = operator for opfamily %u", opfamily);
  		expr = make_opclause(oproid, BOOLOID, false,
  							 (Expr *) leftop, (Expr *) prefix_const,
  							 InvalidOid, collation);
  		result = list_make1(make_simple_restrictinfo(expr));
  		return result;
  	}
  
  	/*
  	 * Otherwise, we have a nonempty required prefix of the values.
  	 *
  	 * We can always say "x >= prefix".
  	 */
  	oproid = get_opfamily_member(opfamily, datatype, datatype,
  								 BTGreaterEqualStrategyNumber);
  	if (oproid == InvalidOid)
  		elog(ERROR, "no >= operator for opfamily %u", opfamily);
  	expr = make_opclause(oproid, BOOLOID, false,
  						 (Expr *) leftop, (Expr *) prefix_const,
  						 InvalidOid, collation);
  	result = list_make1(make_simple_restrictinfo(expr));
  
  	/*-------
  	 * If we can create a string larger than the prefix, we can say
  	 * "x < greaterstr".  NB: we rely on make_greater_string() to generate
  	 * a guaranteed-greater string, not just a probably-greater string.
  	 * In general this is only guaranteed in C locale, so we'd better be
  	 * using a C-locale index collation.
  	 *-------
  	 */
  	oproid = get_opfamily_member(opfamily, datatype, datatype,
  								 BTLessStrategyNumber);
  	if (oproid == InvalidOid)
  		elog(ERROR, "no < operator for opfamily %u", opfamily);
  	fmgr_info(get_opcode(oproid), &ltproc);
  	greaterstr = make_greater_string(prefix_const, &ltproc, collation);
  	if (greaterstr)
  	{
  		expr = make_opclause(oproid, BOOLOID, false,
  							 (Expr *) leftop, (Expr *) greaterstr,
  							 InvalidOid, collation);
  		result = lappend(result, make_simple_restrictinfo(expr));
  	}
  
  	return result;
  }
  
  /*
   * Given a leftop and a rightop, and an inet-family sup/sub operator,
   * generate suitable indexqual condition(s).  expr_op is the original
   * operator, and opfamily is the index opfamily.
   */
  static List *
  network_prefix_quals(Node *leftop, Oid expr_op, Oid opfamily, Datum rightop)
  {
  	bool		is_eq;
  	Oid			datatype;
  	Oid			opr1oid;
  	Oid			opr2oid;
  	Datum		opr1right;
  	Datum		opr2right;
  	List	   *result;
  	Expr	   *expr;
  
  	switch (expr_op)
  	{
  		case OID_INET_SUB_OP:
  			datatype = INETOID;
  			is_eq = false;
  			break;
  		case OID_INET_SUBEQ_OP:
  			datatype = INETOID;
  			is_eq = true;
  			break;
  		default:
  			elog(ERROR, "unexpected operator: %u", expr_op);
  			return NIL;
  	}
  
  	/*
  	 * create clause "key >= network_scan_first( rightop )", or ">" if the
  	 * operator disallows equality.
  	 */
  	if (is_eq)
  	{
  		opr1oid = get_opfamily_member(opfamily, datatype, datatype,
  									  BTGreaterEqualStrategyNumber);
  		if (opr1oid == InvalidOid)
  			elog(ERROR, "no >= operator for opfamily %u", opfamily);
  	}
  	else
  	{
  		opr1oid = get_opfamily_member(opfamily, datatype, datatype,
  									  BTGreaterStrategyNumber);
  		if (opr1oid == InvalidOid)
  			elog(ERROR, "no > operator for opfamily %u", opfamily);
  	}
  
  	opr1right = network_scan_first(rightop);
  
  	expr = make_opclause(opr1oid, BOOLOID, false,
  						 (Expr *) leftop,
  						 (Expr *) makeConst(datatype, -1,
  											InvalidOid, /* not collatable */
  											-1, opr1right,
  											false, false),
  						 InvalidOid, InvalidOid);
  	result = list_make1(make_simple_restrictinfo(expr));
  
  	/* create clause "key <= network_scan_last( rightop )" */
  
  	opr2oid = get_opfamily_member(opfamily, datatype, datatype,
  								  BTLessEqualStrategyNumber);
  	if (opr2oid == InvalidOid)
  		elog(ERROR, "no <= operator for opfamily %u", opfamily);
  
  	opr2right = network_scan_last(rightop);
  
  	expr = make_opclause(opr2oid, BOOLOID, false,
  						 (Expr *) leftop,
  						 (Expr *) makeConst(datatype, -1,
  											InvalidOid, /* not collatable */
  											-1, opr2right,
  											false, false),
  						 InvalidOid, InvalidOid);
  	result = lappend(result, make_simple_restrictinfo(expr));
  
  	return result;
  }
  
  /*
   * Handy subroutines for match_special_index_operator() and friends.
   */
  
  /*
   * Generate a Datum of the appropriate type from a C string.
   * Note that all of the supported types are pass-by-ref, so the
   * returned value should be pfree'd if no longer needed.
   */
  static Datum
  string_to_datum(const char *str, Oid datatype)
  {
  	/*
  	 * We cheat a little by assuming that CStringGetTextDatum() will do for
  	 * bpchar and varchar constants too...
  	 */
  	if (datatype == NAMEOID)
  		return DirectFunctionCall1(namein, CStringGetDatum(str));
  	else if (datatype == BYTEAOID)
  		return DirectFunctionCall1(byteain, CStringGetDatum(str));
  	else
  		return CStringGetTextDatum(str);
  }
  
  /*
   * Generate a Const node of the appropriate type from a C string.
   */
  static Const *
  string_to_const(const char *str, Oid datatype)
  {
  	Datum		conval = string_to_datum(str, datatype);
  	Oid			collation;
  	int			constlen;
  
  	/*
  	 * We only need to support a few datatypes here, so hard-wire properties
  	 * instead of incurring the expense of catalog lookups.
  	 */
  	switch (datatype)
  	{
  		case TEXTOID:
  		case VARCHAROID:
  		case BPCHAROID:
  			collation = DEFAULT_COLLATION_OID;
  			constlen = -1;
  			break;
  
  		case NAMEOID:
  			collation = InvalidOid;
  			constlen = NAMEDATALEN;
  			break;
  
  		case BYTEAOID:
  			collation = InvalidOid;
  			constlen = -1;
  			break;
  
  		default:
  			elog(ERROR, "unexpected datatype in string_to_const: %u",
  				 datatype);
  			return NULL;
  	}
  
  	return makeConst(datatype, -1, collation, constlen,
  					 conval, false, false);
  }
  