Fix inconsistent RestrictInfo serial numbers

Richard Guo · Richard Guo · commit 78b1c553bb1c · 2024-11-08T11:24:26.000+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
@@ -2657,11 +2657,18 @@ 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),
@@ -2674,6 +2681,7 @@ 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;
