Fix old oversight in join removal logic.

Commit 9e7e29c75ad441450f9b8287bd51c13521641e3b introduced an Assert that
join removal didn't reduce the eval_at set of any PlaceHolderVar to empty.
At first glance it looks like join_is_removable ensures that's true --- but
actually, the loop in join_is_removable skips PlaceHolderVars that are not
referenced above the join due to be removed.  So, if we don't want any
empty eval_at sets, the right thing to do is to delete any now-unreferenced
PlaceHolderVars from the data structure entirely.

Per fuzz testing by Andreas Seltenreich.  Back-patch to 9.3 where the
aforesaid Assert was added.

diff --git a/src/backend/optimizer/plan/analyzejoins.c b/src/backend/optimizer/plan/analyzejoins.c
index 470db87817515a2d1217feec963c3a811d13787e..dfb2e378312ecf460dedf6a038f0ced112534e31 100644 (file)
--- a/src/backend/optimizer/plan/analyzejoins.c
+++ b/src/backend/optimizer/plan/analyzejoins.c
@@ -464,16 +464,24 @@ remove_rel_from_query(PlannerInfo *root, int relid, Relids joinrelids)
        }
 
        /*
-        * Likewise remove references from PlaceHolderVar data structures.
+        * Likewise remove references from PlaceHolderVar data structures,
+        * removing any no-longer-needed placeholders entirely.
         */
-       foreach(l, root->placeholder_list)
+       for (l = list_head(root->placeholder_list); l != NULL; l = nextl)
        {
                PlaceHolderInfo *phinfo = (PlaceHolderInfo *) lfirst(l);
 
-               phinfo->ph_eval_at = bms_del_member(phinfo->ph_eval_at, relid);
-               Assert(!bms_is_empty(phinfo->ph_eval_at));
-               Assert(!bms_is_member(relid, phinfo->ph_lateral));
-               phinfo->ph_needed = bms_del_member(phinfo->ph_needed, relid);
+               nextl = lnext(l);
+               if (bms_is_subset(phinfo->ph_needed, joinrelids))
+                       root->placeholder_list = list_delete_ptr(root->placeholder_list,
+                                                                                                        phinfo);
+               else
+               {
+                       phinfo->ph_eval_at = bms_del_member(phinfo->ph_eval_at, relid);
+                       Assert(!bms_is_empty(phinfo->ph_eval_at));
+                       Assert(!bms_is_member(relid, phinfo->ph_lateral));
+                       phinfo->ph_needed = bms_del_member(phinfo->ph_needed, relid);
+               }
        }
 
        /*

diff --git a/src/test/regress/expected/join.out b/src/test/regress/expected/join.out
index 4ba3bc73fea9d1d9509be536290b103aecdd11cb..d08f7052c6b2521bfb44e24cbbc4ae862019865e 100644 (file)
--- a/src/test/regress/expected/join.out
+++ b/src/test/regress/expected/join.out
@@ -3862,6 +3862,22 @@ SELECT * FROM
  1 | 4567890123456789 | -4567890123456789 | 4567890123456789
 (5 rows)
 
+rollback;
+-- another join removal bug: we must clean up correctly when removing a PHV
+begin;
+create temp table uniquetbl (f1 text unique);
+explain (costs off)
+select t1.* from
+  uniquetbl as t1
+  left join (select *, '***'::text as d1 from uniquetbl) t2
+  on t1.f1 = t2.f1
+  left join uniquetbl t3
+  on t2.d1 = t3.f1;
+        QUERY PLAN        
+--------------------------
+ Seq Scan on uniquetbl t1
+(1 row)
+
 rollback;
 -- bug #8444: we've historically allowed duplicate aliases within aliased JOINs
 select * from

diff --git a/src/test/regress/sql/join.sql b/src/test/regress/sql/join.sql
index a27ca3f8bb924a7eaef0d0eba126b7187254c7da..43ca7f16c24edb91c3395a14ab2149239f2f6d34 100644 (file)
--- a/src/test/regress/sql/join.sql
+++ b/src/test/regress/sql/join.sql
@@ -1247,6 +1247,21 @@ SELECT * FROM
 
 rollback;
 
+-- another join removal bug: we must clean up correctly when removing a PHV
+begin;
+
+create temp table uniquetbl (f1 text unique);
+
+explain (costs off)
+select t1.* from
+  uniquetbl as t1
+  left join (select *, '***'::text as d1 from uniquetbl) t2
+  on t1.f1 = t2.f1
+  left join uniquetbl t3
+  on t2.d1 = t3.f1;
+
+rollback;
+
 -- bug #8444: we've historically allowed duplicate aliases within aliased JOINs
 
 select * from