Fix inconsistent RestrictInfo serial numbers

Richard Guo · Richard Guo · commit f00ab1fd156e · 2024-11-08T11:21:11.000+09:00
When we generate multiple clones of the same qual condition to cope with outer join identity 3, we need to ensure that all the clones get the same serial number. To achieve this, we reset the root->last_rinfo_serial counter each time we produce RestrictInfo(s) from the qual list (see deconstruct_distribute_oj_quals). This approach works only if we ensure that we are not changing the qual list in any way that'd affect the number of RestrictInfos built from it. However, with b262ad4, an IS NULL qual on a NOT NULL column might result in an additional constant-FALSE RestrictInfo. And different versions of the same qual clause can lead to different conclusions about whether it can be reduced to constant-FALSE. This would affect the number of RestrictInfos built from the qual list for different versions, causing inconsistent RestrictInfo serial numbers across multiple clones of the same qual. This inconsistency can confuse users of these serial numbers, such as rebuild_joinclause_attr_needed, and lead to planner errors such as "ERROR: variable not found in subplan target lists". To fix, reset the root->last_rinfo_serial counter after generating the additional constant-FALSE RestrictInfo. Back-patch to v17 where the issue crept in. In v17, I failed to make a test case that would expose this bug, so no test case for v17. Author: Richard Guo Discussion: https://postgr.es/m/CAMbWs4-B6kafn+LmPuh-TYFwFyEm-vVj3Qqv7Yo-69CEv14rRg@mail.gmail.com
diff --git a/src/backend/optimizer/plan/initsplan.c b/src/backend/optimizer/plan/initsplan.c
@@ -2767,11 +2767,18 @@ add_base_clause_to_rel(PlannerInfo *root, Index relid,
 
 		/*
 		 * Substitute the origin qual with constant-FALSE if it is provably
-		 * always false.  Note that we keep the same rinfo_serial.
+		 * always false.
+		 *
+		 * Note that we need to keep the same rinfo_serial, since it is in
+		 * practice the same condition.  We also need to reset the
+		 * last_rinfo_serial counter, which is essential to ensure that the
+		 * RestrictInfos for the "same" qual condition get identical serial
+		 * numbers (see deconstruct_distribute_oj_quals).
 		 */
 		if (restriction_is_always_false(root, restrictinfo))
 		{
 			int			save_rinfo_serial = restrictinfo->rinfo_serial;
+			int			save_last_rinfo_serial = root->last_rinfo_serial;
 
 			restrictinfo = make_restrictinfo(root,
 											 (Expr *) makeBoolConst(false, false),
@@ -2784,6 +2791,7 @@ add_base_clause_to_rel(PlannerInfo *root, Index relid,
 											 restrictinfo->incompatible_relids,
 											 restrictinfo->outer_relids);
 			restrictinfo->rinfo_serial = save_rinfo_serial;
+			root->last_rinfo_serial = save_last_rinfo_serial;
 		}
 	}
 
diff --git a/src/backend/optimizer/util/joininfo.c b/src/backend/optimizer/util/joininfo.c
@@ -106,12 +106,19 @@ add_join_clause_to_rels(PlannerInfo *root,
 		return;
 
 	/*
-	 * Substitute constant-FALSE for the origin qual if it is always false.
-	 * Note that we keep the same rinfo_serial.
+	 * Substitute the origin qual with constant-FALSE if it is provably always
+	 * false.
+	 *
+	 * Note that we need to keep the same rinfo_serial, since it is in
+	 * practice the same condition.  We also need to reset the
+	 * last_rinfo_serial counter, which is essential to ensure that the
+	 * RestrictInfos for the "same" qual condition get identical serial
+	 * numbers (see deconstruct_distribute_oj_quals).
 	 */
 	if (restriction_is_always_false(root, restrictinfo))
 	{
 		int			save_rinfo_serial = restrictinfo->rinfo_serial;
+		int			save_last_rinfo_serial = root->last_rinfo_serial;
 
 		restrictinfo = make_restrictinfo(root,
 										 (Expr *) makeBoolConst(false, false),
@@ -124,6 +131,7 @@ add_join_clause_to_rels(PlannerInfo *root,
 										 restrictinfo->incompatible_relids,
 										 restrictinfo->outer_relids);
 		restrictinfo->rinfo_serial = save_rinfo_serial;
+		root->last_rinfo_serial = save_last_rinfo_serial;
 	}
 
 	cur_relid = -1;
diff --git a/src/test/regress/expected/predicate.out b/src/test/regress/expected/predicate.out
@@ -290,3 +290,31 @@ SELECT * FROM pred_parent WHERE a IS NULL;
 (2 rows)
 
 DROP TABLE pred_parent, pred_child;
+-- Validate the additional constant-FALSE qual does not cause inconsistent
+-- RestrictInfo serial numbers
+CREATE TABLE pred_tab (a int PRIMARY KEY, b int);
+INSERT INTO pred_tab SELECT i, i FROM generate_series(1, 10)i;
+ANALYZE pred_tab;
+EXPLAIN (COSTS OFF)
+SELECT 1 FROM pred_tab t1
+    LEFT JOIN
+        (pred_tab t2 LEFT JOIN pred_tab t3 ON t2.a = t3.a) ON TRUE
+    LEFT JOIN pred_tab t4 ON t1.a IS NULL AND t1.b = 1
+    RIGHT JOIN pred_tab t5 ON t1.b = t5.b;
+                    QUERY PLAN                     
+---------------------------------------------------
+ Hash Right Join
+   Hash Cond: (t1.b = t5.b)
+   ->  Nested Loop Left Join
+         ->  Nested Loop Left Join
+               Join Filter: (false AND (t1.b = 1))
+               ->  Seq Scan on pred_tab t1
+               ->  Result
+                     One-Time Filter: false
+         ->  Materialize
+               ->  Seq Scan on pred_tab t2
+   ->  Hash
+         ->  Seq Scan on pred_tab t5
+(12 rows)
+
+DROP TABLE pred_tab;
diff --git a/src/test/regress/sql/predicate.sql b/src/test/regress/sql/predicate.sql
@@ -147,3 +147,18 @@ EXPLAIN (COSTS OFF)
 SELECT * FROM pred_parent WHERE a IS NULL;
 
 DROP TABLE pred_parent, pred_child;
+
+-- Validate the additional constant-FALSE qual does not cause inconsistent
+-- RestrictInfo serial numbers
+CREATE TABLE pred_tab (a int PRIMARY KEY, b int);
+INSERT INTO pred_tab SELECT i, i FROM generate_series(1, 10)i;
+ANALYZE pred_tab;
+
+EXPLAIN (COSTS OFF)
+SELECT 1 FROM pred_tab t1
+    LEFT JOIN
+        (pred_tab t2 LEFT JOIN pred_tab t3 ON t2.a = t3.a) ON TRUE
+    LEFT JOIN pred_tab t4 ON t1.a IS NULL AND t1.b = 1
+    RIGHT JOIN pred_tab t5 ON t1.b = t5.b;
+
+DROP TABLE pred_tab;
