From 84d59123ba6cec8717368ce9cefa290b711d7b3d Mon Sep 17 00:00:00 2001
From: Ashutosh Bapat <ashutosh.bapat@enterprisedb.com>
Date: Wed, 26 Jul 2023 12:08:55 +0530
Subject: [PATCH 2/2] Reuse child_relids bitmapset in partitionwise joinrels

Bitmapsets containing child relids consume large memory when thousands of
partitions are involved. Create them once, use multiple times and free them up
once their use is over.

Ashutosh Bapat
---
 src/backend/optimizer/path/joinrels.c | 10 ++++++----
 src/backend/optimizer/util/relnode.c  | 18 +++---------------
 src/include/optimizer/pathnode.h      |  3 ++-
 3 files changed, 11 insertions(+), 20 deletions(-)

diff --git a/src/backend/optimizer/path/joinrels.c b/src/backend/optimizer/path/joinrels.c
index d03ace50a1..1feb1f99c0 100644
--- a/src/backend/optimizer/path/joinrels.c
+++ b/src/backend/optimizer/path/joinrels.c
@@ -1526,6 +1526,7 @@ try_partitionwise_join(PlannerInfo *root, RelOptInfo *rel1, RelOptInfo *rel2,
 		RelOptInfo *child_joinrel;
 		AppendRelInfo **appinfos;
 		int			nappinfos;
+		Bitmapset  *child_relids = NULL;
 
 		if (joinrel->partbounds_merged)
 		{
@@ -1621,9 +1622,8 @@ try_partitionwise_join(PlannerInfo *root, RelOptInfo *rel1, RelOptInfo *rel2,
 											   child_rel2->relids);
 
 		/* Find the AppendRelInfo structures */
-		appinfos = find_appinfos_by_relids(root,
-										   bms_union(child_rel1->relids,
-													 child_rel2->relids),
+		child_relids = bms_union(child_rel1->relids, child_rel2->relids);
+		appinfos = find_appinfos_by_relids(root, child_relids,
 										   &nappinfos);
 
 		/*
@@ -1641,7 +1641,8 @@ try_partitionwise_join(PlannerInfo *root, RelOptInfo *rel1, RelOptInfo *rel2,
 		{
 			child_joinrel = build_child_join_rel(root, child_rel1, child_rel2,
 												 joinrel, child_restrictlist,
-												 child_sjinfo);
+												 child_sjinfo, appinfos,
+												 nappinfos);
 			joinrel->part_rels[cnt_parts] = child_joinrel;
 			joinrel->live_parts = bms_add_member(joinrel->live_parts, cnt_parts);
 			joinrel->all_partrels = bms_add_members(joinrel->all_partrels,
@@ -1659,6 +1660,7 @@ try_partitionwise_join(PlannerInfo *root, RelOptInfo *rel1, RelOptInfo *rel2,
 									child_restrictlist);
 
 		pfree(appinfos);
+		bms_free(child_relids);
 	}
 }
 
diff --git a/src/backend/optimizer/util/relnode.c b/src/backend/optimizer/util/relnode.c
index 5d83f60eb9..81044f12cc 100644
--- a/src/backend/optimizer/util/relnode.c
+++ b/src/backend/optimizer/util/relnode.c
@@ -853,15 +853,15 @@ build_join_rel(PlannerInfo *root,
  * 'restrictlist': list of RestrictInfo nodes that apply to this particular
  *		pair of joinable relations
  * 'sjinfo': child join's join-type details
+ * 'appinfos' and 'nappinfos': AppendRelInfo array for child relids
  */
 RelOptInfo *
 build_child_join_rel(PlannerInfo *root, RelOptInfo *outer_rel,
 					 RelOptInfo *inner_rel, RelOptInfo *parent_joinrel,
-					 List *restrictlist, SpecialJoinInfo *sjinfo)
+					 List *restrictlist, SpecialJoinInfo *sjinfo,
+					 AppendRelInfo **appinfos, int nappinfos)
 {
 	RelOptInfo *joinrel = makeNode(RelOptInfo);
-	AppendRelInfo **appinfos;
-	int			nappinfos;
 
 	/* Only joins between "other" relations land here. */
 	Assert(IS_OTHER_REL(outer_rel) && IS_OTHER_REL(inner_rel));
@@ -869,16 +869,6 @@ build_child_join_rel(PlannerInfo *root, RelOptInfo *outer_rel,
 	/* The parent joinrel should have consider_partitionwise_join set. */
 	Assert(parent_joinrel->consider_partitionwise_join);
 
-	/*
-	 * Find the AppendRelInfo structures for the child baserels.  We'll need
-	 * these for computing the child join's relid set, and later for mapping
-	 * Vars to the child rel.
-	 */
-	appinfos = find_appinfos_by_relids(root,
-									   bms_union(outer_rel->relids,
-												 inner_rel->relids),
-									   &nappinfos);
-
 	joinrel->reloptkind = RELOPT_OTHER_JOINREL;
 	joinrel->relids = adjust_child_relids(parent_joinrel->relids,
 										  nappinfos, appinfos);
@@ -993,8 +983,6 @@ build_child_join_rel(PlannerInfo *root, RelOptInfo *outer_rel,
 										nappinfos, appinfos,
 										parent_joinrel, joinrel);
 
-	pfree(appinfos);
-
 	return joinrel;
 }
 
diff --git a/src/include/optimizer/pathnode.h b/src/include/optimizer/pathnode.h
index 6e557bebc4..65336c47dc 100644
--- a/src/include/optimizer/pathnode.h
+++ b/src/include/optimizer/pathnode.h
@@ -341,6 +341,7 @@ extern Bitmapset *get_param_path_clause_serials(Path *path);
 extern RelOptInfo *build_child_join_rel(PlannerInfo *root,
 										RelOptInfo *outer_rel, RelOptInfo *inner_rel,
 										RelOptInfo *parent_joinrel, List *restrictlist,
-										SpecialJoinInfo *sjinfo);
+										SpecialJoinInfo *sjinfo,
+										AppendRelInfo **appinfos, int nappinfos);
 
 #endif							/* PATHNODE_H */
-- 
2.25.1