Defend against bogus parameterization of join input paths.

tglsfdc · tglsfdc · commit a798660ebe3f · 2023-06-29T12:12:52.000-04:00
An outer join cannot be formed using an input path that is parameterized by a value that is supposed to be nulled by the outer join. This is obviously nonsensical, and it could lead to a bad plan being selected; although currently it seems that we'll hit various sanity-check assertions first. I think that such cases were formerly prevented by the delay_upper_joins mechanism, but now that that's gone we need an explicit check. (Perhaps we should avoid generating baserel paths that could lead to this situation in the first place; but it seems like having a defense at the join level would be a good idea anyway.) Richard Guo and Tom Lane, per report from Jaime Casanova Discussion: https://postgr.es/m/CAJKUy5g2uZRrUDZJ8p-=giwcSHVUn0c9nmdxPSY0jF0Ov8VoEA@mail.gmail.com
diff --git a/src/backend/optimizer/path/joinpath.c b/src/backend/optimizer/path/joinpath.c
@@ -698,6 +698,17 @@ try_nestloop_path(PlannerInfo *root,
 	Relids		inner_paramrels = PATH_REQ_OUTER(inner_path);
 	Relids		outer_paramrels = PATH_REQ_OUTER(outer_path);
 
+	/*
+	 * If we are forming an outer join at this join, it's nonsensical to use
+	 * an input path that uses the outer join as part of its parameterization.
+	 * (This can happen despite our join order restrictions, since those apply
+	 * to what is in an input relation not what its parameters are.)
+	 */
+	if (extra->sjinfo->ojrelid != 0 &&
+		(bms_is_member(extra->sjinfo->ojrelid, inner_paramrels) ||
+		 bms_is_member(extra->sjinfo->ojrelid, outer_paramrels)))
+		return;
+
 	/*
 	 * Paths are parameterized by top-level parents, so run parameterization
 	 * tests on the parent relids.
@@ -908,6 +919,17 @@ try_mergejoin_path(PlannerInfo *root,
 		return;
 	}
 
+	/*
+	 * If we are forming an outer join at this join, it's nonsensical to use
+	 * an input path that uses the outer join as part of its parameterization.
+	 * (This can happen despite our join order restrictions, since those apply
+	 * to what is in an input relation not what its parameters are.)
+	 */
+	if (extra->sjinfo->ojrelid != 0 &&
+		(bms_is_member(extra->sjinfo->ojrelid, PATH_REQ_OUTER(inner_path)) ||
+		 bms_is_member(extra->sjinfo->ojrelid, PATH_REQ_OUTER(outer_path))))
+		return;
+
 	/*
 	 * Check to see if proposed path is still parameterized, and reject if the
 	 * parameterization wouldn't be sensible.
@@ -1054,6 +1076,17 @@ try_hashjoin_path(PlannerInfo *root,
 	Relids		required_outer;
 	JoinCostWorkspace workspace;
 
+	/*
+	 * If we are forming an outer join at this join, it's nonsensical to use
+	 * an input path that uses the outer join as part of its parameterization.
+	 * (This can happen despite our join order restrictions, since those apply
+	 * to what is in an input relation not what its parameters are.)
+	 */
+	if (extra->sjinfo->ojrelid != 0 &&
+		(bms_is_member(extra->sjinfo->ojrelid, PATH_REQ_OUTER(inner_path)) ||
+		 bms_is_member(extra->sjinfo->ojrelid, PATH_REQ_OUTER(outer_path))))
+		return;
+
 	/*
 	 * Check to see if proposed path is still parameterized, and reject if the
 	 * parameterization wouldn't be sensible.
diff --git a/src/test/regress/expected/join.out b/src/test/regress/expected/join.out
@@ -5063,6 +5063,29 @@ select 1 from
 ----------
 (0 rows)
 
+--
+-- check a case where we formerly generated invalid parameterized paths
+--
+begin;
+create temp table t (a int unique);
+explain (costs off)
+select 1 from t t1
+  join lateral (select t1.a from (select 1) foo offset 0) as s1 on true
+  join
+    (select 1 from t t2
+       inner join (t t3
+                   left join (t t4 left join t t5 on t4.a = 1)
+                   on t3.a = t4.a)
+       on false
+     where t3.a = coalesce(t5.a,1)) as s2
+  on true;
+        QUERY PLAN        
+--------------------------
+ Result
+   One-Time Filter: false
+(2 rows)
+
+rollback;
 --
 -- check a case in which a PlaceHolderVar forces join order
 --
diff --git a/src/test/regress/sql/join.sql b/src/test/regress/sql/join.sql
@@ -1751,6 +1751,28 @@ select 1 from
   on false,
   lateral (select i4.f1, ss1.n from int8_tbl as i8 limit 1) as ss3;
 
+--
+-- check a case where we formerly generated invalid parameterized paths
+--
+
+begin;
+
+create temp table t (a int unique);
+
+explain (costs off)
+select 1 from t t1
+  join lateral (select t1.a from (select 1) foo offset 0) as s1 on true
+  join
+    (select 1 from t t2
+       inner join (t t3
+                   left join (t t4 left join t t5 on t4.a = 1)
+                   on t3.a = t4.a)
+       on false
+     where t3.a = coalesce(t5.a,1)) as s2
+  on true;
+
+rollback;
+
 --
 -- check a case in which a PlaceHolderVar forces join order
 --
