Teach bitmap path generation about transforming OR-clauses to SAOP's

When optimizer generates bitmap paths, it considers breaking OR-clause
arguments one-by-one.  But now, a group of similar OR-clauses can be
transformed into SAOP during index matching.  So, bitmap paths should
keep up.

This commit teaches bitmap paths generation machinery to group similar
OR-clauses into dedicated RestrictInfos.  Those RestrictInfos are considered
both to match index as a whole (as SAOP), or to match as a set of individual
OR-clause argument one-by-one (the old way).

Therefore, bitmap path generation will takes advantage of OR-clauses to SAOP's
transformation.  The old way of handling them is also considered.  So, there
shouldn't be planning regression.

Discussion: https://postgr.es/m/CAPpHfdu5iQOjF93vGbjidsQkhHvY2NSm29duENYH_cbhC6x%2BMg%40mail.gmail.com
Author: Alexander Korotkov, Andrey Lepikhov
Reviewed-by: Alena Rybakina, Andrei Lepikhov, Jian he, Robert Haas
Reviewed-by: Peter Geoghegan

1 files changed, 428 insertions, 2 deletions

diff --git a/src/backend/optimizer/path/indxpath.c b/src/backend/optimizer/path/indxpath.c
index 61b18482410..5d8d0c389c9 100644
--- a/src/backend/optimizer/path/indxpath.c
+++ b/src/backend/optimizer/path/indxpath.c
@@ -1174,6 +1174,383 @@ build_paths_for_OR(PlannerInfo *root, RelOptInfo *rel,
 }
 
 /*
+ * Utility structure used to group similar OR-clause arguments in
+ * group_similar_or_args().  It represents information about the OR-clause
+ * argument and its matching index key.
+ */
+typedef struct
+{
+	int			indexnum;		/* index of the matching index, or -1 if no
+								 * matching index */
+	int			colnum;			/* index of the matching column, or -1 if no
+								 * matching index */
+	Oid			opno;			/* OID of the OpClause operator, or InvalidOid
+								 * if not an OpExpr */
+	Oid			inputcollid;	/* OID of the OpClause input collation */
+	int			argindex;		/* index of the clause in the list of
+								 * arguments */
+} OrArgIndexMatch;
+
+/*
+ * Comparison function for OrArgIndexMatch which provides sort order placing
+ * similar OR-clause arguments together.
+ */
+static int
+or_arg_index_match_cmp(const void *a, const void *b)
+{
+	const OrArgIndexMatch *match_a = (const OrArgIndexMatch *) a;
+	const OrArgIndexMatch *match_b = (const OrArgIndexMatch *) b;
+
+	if (match_a->indexnum < match_b->indexnum)
+		return -1;
+	else if (match_a->indexnum > match_b->indexnum)
+		return 1;
+
+	if (match_a->colnum < match_b->colnum)
+		return -1;
+	else if (match_a->colnum > match_b->colnum)
+		return 1;
+
+	if (match_a->opno < match_b->opno)
+		return -1;
+	else if (match_a->opno > match_b->opno)
+		return 1;
+
+	if (match_a->inputcollid < match_b->inputcollid)
+		return -1;
+	else if (match_a->inputcollid > match_b->inputcollid)
+		return 1;
+
+	if (match_a->argindex < match_b->argindex)
+		return -1;
+	else if (match_a->argindex > match_b->argindex)
+		return 1;
+
+	return 0;
+}
+
+/*
+ * group_similar_or_args
+ *		Transform incoming OR-restrictinfo into a list of sub-restrictinfos,
+ *		each of them containing a subset of similar OR-clause arguments from
+ *		the source rinfo.
+ *
+ * Similar OR-clause arguments are of the form "indexkey op constant" having
+ * the same indexkey, operator, and collation.  Constant may comprise either
+ * Const or Param.  It may be employed later, during the
+ * match_clause_to_indexcol() to transform the whole OR-sub-rinfo to an SAOP
+ * clause.
+ *
+ * Returns the processed list of OR-clause arguments.
+ */
+static List *
+group_similar_or_args(PlannerInfo *root, RelOptInfo *rel, RestrictInfo *rinfo)
+{
+	int			n;
+	int			i;
+	int			group_start;
+	OrArgIndexMatch *matches;
+	bool		matched = false;
+	ListCell   *lc;
+	ListCell   *lc2;
+	List	   *orargs;
+	List	   *result = NIL;
+
+	Assert(IsA(rinfo->orclause, BoolExpr));
+	orargs = ((BoolExpr *) rinfo->orclause)->args;
+	n = list_length(orargs);
+
+	/*
+	 * To avoid N^2 behavior, take utility pass along the list of OR-clause
+	 * arguments.  For each argument, fill the OrArgIndexMatch structure,
+	 * which will be used to sort these arguments at the next step.
+	 */
+	i = -1;
+	matches = (OrArgIndexMatch *) palloc(sizeof(OrArgIndexMatch) * n);
+	foreach(lc, orargs)
+	{
+		Node	   *arg = lfirst(lc);
+		RestrictInfo *argrinfo;
+		OpExpr	   *clause;
+		Oid			opno;
+		Node	   *leftop,
+				   *rightop;
+		Node	   *nonConstExpr;
+		int			indexnum;
+		int			colnum;
+
+		i++;
+		matches[i].argindex = i;
+		matches[i].indexnum = -1;
+		matches[i].colnum = -1;
+		matches[i].opno = InvalidOid;
+		matches[i].inputcollid = InvalidOid;
+
+		if (!IsA(arg, RestrictInfo))
+			continue;
+
+		argrinfo = castNode(RestrictInfo, arg);
+
+		/* Only operator clauses can match  */
+		if (!IsA(argrinfo->clause, OpExpr))
+			continue;
+
+		clause = (OpExpr *) argrinfo->clause;
+		opno = clause->opno;
+
+		/* Only binary operators can match  */
+		if (list_length(clause->args) != 2)
+			continue;
+
+		/*
+		 * Ignore any RelabelType node above the operands.  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.
+		 */
+		leftop = get_leftop(clause);
+		if (IsA(leftop, RelabelType))
+			leftop = (Node *) ((RelabelType *) leftop)->arg;
+
+		rightop = get_rightop(clause);
+		if (IsA(rightop, RelabelType))
+			rightop = (Node *) ((RelabelType *) rightop)->arg;
+
+		/*
+		 * Check for clauses of the form: (indexkey operator constant) or
+		 * (constant operator indexkey).  But we don't know a particular index
+		 * yet.  First check for a constant, which must be Const or Param.
+		 * That's cheaper than search for an index key among all indexes.
+		 */
+		if (IsA(leftop, Const) || IsA(leftop, Param))
+		{
+			opno = get_commutator(opno);
+
+			if (!OidIsValid(opno))
+			{
+				/* commutator doesn't exist, we can't reverse the order */
+				continue;
+			}
+			nonConstExpr = rightop;
+		}
+		else if (IsA(rightop, Const) || IsA(rightop, Param))
+		{
+			nonConstExpr = leftop;
+		}
+		else
+		{
+			continue;
+		}
+
+		/*
+		 * Match non-constant part to the index key.  It's possible that a
+		 * single non-constant part matches multiple index keys.  It's OK, we
+		 * just stop with first matching index key.  Given that this choice is
+		 * determined the same for every clause, we will group similar clauses
+		 * together anyway.
+		 */
+		indexnum = 0;
+		foreach(lc2, rel->indexlist)
+		{
+			IndexOptInfo *index = (IndexOptInfo *) lfirst(lc2);
+
+			/* Ignore index if it doesn't support bitmap scans */
+			if (!index->amhasgetbitmap)
+				continue;
+
+			for (colnum = 0; colnum < index->nkeycolumns; colnum++)
+			{
+				if (match_index_to_operand(nonConstExpr, colnum, index))
+				{
+					matches[i].indexnum = indexnum;
+					matches[i].colnum = colnum;
+					matches[i].opno = opno;
+					matches[i].inputcollid = clause->inputcollid;
+					matched = true;
+					break;
+				}
+			}
+
+			/*
+			 * Stop looping through the indexes, if we managed to match
+			 * nonConstExpr to any index column.
+			 */
+			if (matches[i].indexnum >= 0)
+				break;
+			indexnum++;
+		}
+	}
+
+	/*
+	 * Fast-path check: if no clause is matching to the index column, we can
+	 * just give up at this stage and return the clause list as-is.
+	 */
+	if (!matched)
+	{
+		pfree(matches);
+		return orargs;
+	}
+
+	/* Sort clauses to make similar clauses go together */
+	qsort(matches, n, sizeof(OrArgIndexMatch), or_arg_index_match_cmp);
+
+	/*
+	 * Group similar clauses into single sub-restrictinfo. Side effect: the
+	 * resulting list of restrictions will be sorted by indexnum and colnum.
+	 */
+	group_start = 0;
+	for (i = 1; i <= n; i++)
+	{
+		/* Check if it's a group boundary */
+		if (group_start >= 0 &&
+			(i == n ||
+			 matches[i].indexnum != matches[group_start].indexnum ||
+			 matches[i].colnum != matches[group_start].colnum ||
+			 matches[i].opno != matches[group_start].opno ||
+			 matches[i].inputcollid != matches[group_start].inputcollid ||
+			 matches[i].indexnum == -1))
+		{
+			/*
+			 * One clause in group: add it "as is" to the upper-level OR.
+			 */
+			if (i - group_start == 1)
+			{
+				result = lappend(result,
+								 list_nth(orargs,
+										  matches[group_start].argindex));
+			}
+			else
+			{
+				/*
+				 * Two or more clauses in a group: create a nested OR.
+				 */
+				List	   *args = NIL;
+				List	   *rargs = NIL;
+				RestrictInfo *subrinfo;
+				int			j;
+
+				Assert(i - group_start >= 2);
+
+				/* Construct the list of nested OR arguments */
+				for (j = group_start; j < i; j++)
+				{
+					Node	   *arg = list_nth(orargs, matches[j].argindex);
+
+					rargs = lappend(rargs, arg);
+					if (IsA(arg, RestrictInfo))
+						args = lappend(args, ((RestrictInfo *) arg)->clause);
+					else
+						args = lappend(args, arg);
+				}
+
+				/* Construct the nested OR and wrap it with RestrictInfo */
+				subrinfo = make_plain_restrictinfo(root,
+												   make_orclause(args),
+												   make_orclause(rargs),
+												   rinfo->is_pushed_down,
+												   rinfo->has_clone,
+												   rinfo->is_clone,
+												   rinfo->pseudoconstant,
+												   rinfo->security_level,
+												   rinfo->required_relids,
+												   rinfo->incompatible_relids,
+												   rinfo->outer_relids);
+				result = lappend(result, subrinfo);
+			}
+
+			group_start = i;
+		}
+	}
+	pfree(matches);
+	return result;
+}
+
+/*
+ * make_bitmap_paths_for_or_group
+ *		Generate bitmap paths for a group of similar OR-clause arguments
+ *		produced by group_similar_or_args().
+ *
+ * This function considers two cases: (1) matching a group of clauses to
+ * the index as a whole, and (2) matching the individual clauses one-by-one.
+ * (1) typically comprises an optimal solution.  If not, (2) typically
+ * comprises fair alternative.
+ *
+ * Ideally, we could consider all arbitrary splits of arguments into
+ * subgroups, but that could lead to unacceptable computational complexity.
+ * This is why we only consider two cases of above.
+ */
+static List *
+make_bitmap_paths_for_or_group(PlannerInfo *root, RelOptInfo *rel,
+							   RestrictInfo *ri, List *other_clauses)
+{
+	List	   *jointlist = NIL;
+	List	   *splitlist = NIL;
+	ListCell   *lc;
+	List	   *orargs;
+	List	   *args = ((BoolExpr *) ri->orclause)->args;
+	Cost		jointcost = 0.0,
+				splitcost = 0.0;
+	Path	   *bitmapqual;
+	List	   *indlist;
+
+	/*
+	 * First, try to match the whole group to the one index.
+	 */
+	orargs = list_make1(ri);
+	indlist = build_paths_for_OR(root, rel,
+								 orargs,
+								 other_clauses);
+	if (indlist != NIL)
+	{
+		bitmapqual = choose_bitmap_and(root, rel, indlist);
+		jointcost = bitmapqual->total_cost;
+		jointlist = list_make1(bitmapqual);
+	}
+
+	/*
+	 * If we manage to find a bitmap scan, which uses the group of OR-clause
+	 * arguments as a whole, we can skip matching OR-clause arguments
+	 * one-by-one as long as there are no other clauses, which can bring more
+	 * efficiency to one-by-one case.
+	 */
+	if (jointlist != NIL && other_clauses == NIL)
+		return jointlist;
+
+	/*
+	 * Also try to match all containing clauses one-by-one.
+	 */
+	foreach(lc, args)
+	{
+		orargs = list_make1(lfirst(lc));
+
+		indlist = build_paths_for_OR(root, rel,
+									 orargs,
+									 other_clauses);
+
+		if (indlist == NIL)
+		{
+			splitlist = NIL;
+			break;
+		}
+
+		bitmapqual = choose_bitmap_and(root, rel, indlist);
+		splitcost += bitmapqual->total_cost;
+		splitlist = lappend(splitlist, bitmapqual);
+	}
+
+	/*
+	 * Pick the best option.
+	 */
+	if (splitlist == NIL)
+		return jointlist;
+	else if (jointlist == NIL)
+		return splitlist;
+	else
+		return (jointcost < splitcost) ? jointlist : splitlist;
+}
+
+
+/*
  * 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
@@ -1203,6 +1580,8 @@ generate_bitmap_or_paths(PlannerInfo *root, RelOptInfo *rel,
 		List	   *pathlist;
 		Path	   *bitmapqual;
 		ListCell   *j;
+		List	   *groupedArgs;
+		List	   *inner_other_clauses = NIL;
 
 		/* Ignore RestrictInfos that aren't ORs */
 		if (!restriction_is_or_clause(rinfo))
@@ -1213,7 +1592,29 @@ generate_bitmap_or_paths(PlannerInfo *root, RelOptInfo *rel,
 		 * the OR, else we can't use it.
 		 */
 		pathlist = NIL;
-		foreach(j, ((BoolExpr *) rinfo->orclause)->args)
+
+		/*
+		 * Group the similar OR-clause arguments into dedicated RestrictInfos,
+		 * because each of those RestrictInfos has a chance to match the index
+		 * as a whole.
+		 */
+		groupedArgs = group_similar_or_args(root, rel, rinfo);
+
+		if (groupedArgs != ((BoolExpr *) rinfo->orclause)->args)
+		{
+			/*
+			 * Some parts of the rinfo were probably grouped.  In this case,
+			 * we have a set of sub-rinfos that together are an exact
+			 * duplicate of rinfo.  Thus, we need to remove the rinfo from
+			 * other clauses. match_clauses_to_index detects duplicated
+			 * iclauses by comparing pointers to original rinfos that would be
+			 * different.  So, we must delete rinfo to avoid de-facto
+			 * duplicated clauses in the index clauses list.
+			 */
+			inner_other_clauses = list_delete(list_copy(all_clauses), rinfo);
+		}
+
+		foreach(j, groupedArgs)
 		{
 			Node	   *orarg = (Node *) lfirst(j);
 			List	   *indlist;
@@ -1233,12 +1634,34 @@ generate_bitmap_or_paths(PlannerInfo *root, RelOptInfo *rel,
 															   andargs,
 															   all_clauses));
 			}
+			else if (restriction_is_or_clause(castNode(RestrictInfo, orarg)))
+			{
+				RestrictInfo *ri = castNode(RestrictInfo, orarg);
+
+				/*
+				 * Generate bitmap paths for the group of similar OR-clause
+				 * arguments.
+				 */
+				indlist = make_bitmap_paths_for_or_group(root,
+														 rel, ri,
+														 inner_other_clauses);
+
+				if (indlist == NIL)
+				{
+					pathlist = NIL;
+					break;
+				}
+				else
+				{
+					pathlist = list_concat(pathlist, indlist);
+					continue;
+				}
+			}
 			else
 			{
 				RestrictInfo *ri = castNode(RestrictInfo, orarg);
 				List	   *orargs;
 
-				Assert(!restriction_is_or_clause(ri));
 				orargs = list_make1(ri);
 
 				indlist = build_paths_for_OR(root, rel,
@@ -1264,6 +1687,9 @@ generate_bitmap_or_paths(PlannerInfo *root, RelOptInfo *rel,
 			pathlist = lappend(pathlist, bitmapqual);
 		}
 
+		if (inner_other_clauses != NIL)
+			list_free(inner_other_clauses);
+
 		/*
 		 * If we have a match for every arm, then turn them into a
 		 * BitmapOrPath, and add to result list.