Fix Memoize to work with partitionwise joining.

A couple of places weren't up to speed for this.  By sheer good
luck, we didn't fail but just selected a non-memoized join plan,
at least in the test case we have.  Nonetheless, it's a bug,
and I'm not quite sure that it couldn't have worse consequences
in other examples.  So back-patch to v14 where Memoize came in.

Richard Guo

Discussion: https://postgr.es/m/CAMbWs48GkNom272sfp0-WeD6_0HSR19BJ4H1c9ZKSfbVnJsvRg@mail.gmail.com

src/backend/optimizer/path/joinpath.c

@@ -490,6 +490,7 @@ get_memoize_path(PlannerInfo *root, RelOptInfo *innerrel,
 				 Path *outer_path, JoinType jointype,
 				 JoinPathExtraData *extra)
 {
+	RelOptInfo *top_outerrel;
 	List	   *param_exprs;
 	List	   *hash_operators;
 	ListCell   *lc;
@@ -579,10 +580,21 @@ get_memoize_path(PlannerInfo *root, RelOptInfo *innerrel,
 			return NULL;
 	}
 
+	/*
+	 * When considering a partitionwise join, we have clauses that reference
+	 * the outerrel's top parent not outerrel itself.
+	 */
+	if (outerrel->reloptkind == RELOPT_OTHER_MEMBER_REL)
+		top_outerrel = find_base_rel(root, bms_singleton_member(outerrel->top_parent_relids));
+	else if (outerrel->reloptkind == RELOPT_OTHER_JOINREL)
+		top_outerrel = find_join_rel(root, outerrel->top_parent_relids);
+	else
+		top_outerrel = outerrel;
+
 	/* Check if we have hash ops for each parameter to the path */
 	if (paraminfo_get_equal_hashops(root,
 									inner_path->param_info,
-									outerrel,
+									top_outerrel,
 									innerrel,
 									&param_exprs,
 									&hash_operators,

src/backend/optimizer/util/pathnode.c

@@ -4176,6 +4176,7 @@ do { \
 
 				FLAT_COPY_PATH(mpath, path, MemoizePath);
 				REPARAMETERIZE_CHILD_PATH(mpath->subpath);
+				ADJUST_CHILD_ATTRS(mpath->param_exprs);
 				new_path = (Path *) mpath;
 			}
 			break;

src/include/nodes/pathnodes.h

@@ -1508,8 +1508,8 @@ typedef struct MemoizePath
 {
 	Path		path;
 	Path	   *subpath;		/* outerpath to cache tuples from */
-	List	   *hash_operators; /* hash operators for each key */
-	List	   *param_exprs;	/* cache keys */
+	List	   *hash_operators; /* OIDs of hash equality ops for cache keys */
+	List	   *param_exprs;	/* expressions that are cache keys */
 	bool		singlerow;		/* true if the cache entry is to be marked as
 								 * complete after caching the first record. */
 	bool		binary_mode;	/* true when cache key should be compared bit

src/test/regress/expected/memoize.out

@@ -196,6 +196,45 @@ SELECT * FROM strtest s1 INNER JOIN strtest s2 ON s1.t >= s2.t;', false);
 (8 rows)
 
 DROP TABLE strtest;
+-- Ensure memoize works with partitionwise join
+SET enable_partitionwise_join TO on;
+CREATE TABLE prt (a int) PARTITION BY RANGE(a);
+CREATE TABLE prt_p1 PARTITION OF prt FOR VALUES FROM (0) TO (10);
+CREATE TABLE prt_p2 PARTITION OF prt FOR VALUES FROM (10) TO (20);
+INSERT INTO prt VALUES (0), (0), (0), (0);
+INSERT INTO prt VALUES (10), (10), (10), (10);
+CREATE INDEX iprt_p1_a ON prt_p1 (a);
+CREATE INDEX iprt_p2_a ON prt_p2 (a);
+ANALYZE prt;
+SELECT explain_memoize('
+SELECT * FROM prt t1 INNER JOIN prt t2 ON t1.a = t2.a;', false);
+                                     explain_memoize                                      
+------------------------------------------------------------------------------------------
+ Append (actual rows=32 loops=N)
+   ->  Nested Loop (actual rows=16 loops=N)
+         ->  Index Only Scan using iprt_p1_a on prt_p1 t1_1 (actual rows=4 loops=N)
+               Heap Fetches: N
+         ->  Memoize (actual rows=4 loops=N)
+               Cache Key: t1_1.a
+               Cache Mode: logical
+               Hits: 3  Misses: 1  Evictions: Zero  Overflows: 0  Memory Usage: NkB
+               ->  Index Only Scan using iprt_p1_a on prt_p1 t2_1 (actual rows=4 loops=N)
+                     Index Cond: (a = t1_1.a)
+                     Heap Fetches: N
+   ->  Nested Loop (actual rows=16 loops=N)
+         ->  Index Only Scan using iprt_p2_a on prt_p2 t1_2 (actual rows=4 loops=N)
+               Heap Fetches: N
+         ->  Memoize (actual rows=4 loops=N)
+               Cache Key: t1_2.a
+               Cache Mode: logical
+               Hits: 3  Misses: 1  Evictions: Zero  Overflows: 0  Memory Usage: NkB
+               ->  Index Only Scan using iprt_p2_a on prt_p2 t2_2 (actual rows=4 loops=N)
+                     Index Cond: (a = t1_2.a)
+                     Heap Fetches: N
+(21 rows)
+
+DROP TABLE prt;
+RESET enable_partitionwise_join;
 -- Exercise Memoize code that flushes the cache when a parameter changes which
 -- is not part of the cache key.
 -- Ensure we get a Memoize plan

src/test/regress/sql/memoize.sql

@@ -103,6 +103,25 @@ SELECT * FROM strtest s1 INNER JOIN strtest s2 ON s1.t >= s2.t;', false);
 
 DROP TABLE strtest;
 
+-- Ensure memoize works with partitionwise join
+SET enable_partitionwise_join TO on;
+
+CREATE TABLE prt (a int) PARTITION BY RANGE(a);
+CREATE TABLE prt_p1 PARTITION OF prt FOR VALUES FROM (0) TO (10);
+CREATE TABLE prt_p2 PARTITION OF prt FOR VALUES FROM (10) TO (20);
+INSERT INTO prt VALUES (0), (0), (0), (0);
+INSERT INTO prt VALUES (10), (10), (10), (10);
+CREATE INDEX iprt_p1_a ON prt_p1 (a);
+CREATE INDEX iprt_p2_a ON prt_p2 (a);
+ANALYZE prt;
+
+SELECT explain_memoize('
+SELECT * FROM prt t1 INNER JOIN prt t2 ON t1.a = t2.a;', false);
+
+DROP TABLE prt;
+
+RESET enable_partitionwise_join;
+
 -- Exercise Memoize code that flushes the cache when a parameter changes which
 -- is not part of the cache key.