Don't constrain self-join removal due to PHVs

Self-join removal appears to be safe to apply with placeholder variables
as long as we handle PlaceHolderVar in replace_varno_walker() and replace
relid in phinfo->ph_lateral.

Discussion: https://postgr.es/m/18187-831da249cbd2ff8e%40postgresql.org
Author: Richard Guo
Reviewed-by: Andrei Lepikhov

diff --git a/src/backend/optimizer/plan/analyzejoins.c b/src/backend/optimizer/plan/analyzejoins.c
index 00404a8beb0c57a9f5c22e691a4f19bd833b0fcc..c328cbdb8d334f16d01587a1e67e6407176458f3 100644 (file)
--- a/src/backend/optimizer/plan/analyzejoins.c
+++ b/src/backend/optimizer/plan/analyzejoins.c
@@ -453,7 +453,7 @@ remove_rel_from_query(PlannerInfo *root, RelOptInfo *rel,
    {
        PlaceHolderInfo *phinfo = (PlaceHolderInfo *) lfirst(l);
 
-       Assert(!bms_is_member(relid, phinfo->ph_lateral));
+       Assert(sjinfo == NULL || !bms_is_member(relid, phinfo->ph_lateral));
        if (bms_is_subset(phinfo->ph_needed, joinrelids) &&
            bms_is_member(relid, phinfo->ph_eval_at) &&
            !bms_is_member(ojrelid, phinfo->ph_eval_at))
@@ -472,6 +472,8 @@ remove_rel_from_query(PlannerInfo *root, RelOptInfo *rel,
            phinfo->ph_needed = replace_relid(phinfo->ph_needed, relid, subst);
            phinfo->ph_needed = replace_relid(phinfo->ph_needed, ojrelid, subst);
            /* ph_needed might or might not become empty */
+           phinfo->ph_lateral = replace_relid(phinfo->ph_lateral, relid, subst);
+           /* ph_lateral might or might not be empty */
            phv->phrels = replace_relid(phv->phrels, relid, subst);
            phv->phrels = replace_relid(phv->phrels, ojrelid, subst);
            Assert(!bms_is_empty(phv->phrels));
@@ -2115,20 +2117,8 @@ remove_self_joins_one_group(PlannerInfo *root, Relids relids)
            joinrelids = bms_add_member(joinrelids, k);
 
            /*
-            * Be safe to do not remove tables participated in complicated PH
+            * PHVs should not impose any constraints on removing self joins.
             */
-           foreach(lc, root->placeholder_list)
-           {
-               PlaceHolderInfo *phinfo = (PlaceHolderInfo *) lfirst(lc);
-
-               /* there isn't any other place to eval PHV */
-               if (bms_is_subset(phinfo->ph_eval_at, joinrelids) ||
-                   bms_is_subset(phinfo->ph_needed, joinrelids) ||
-                   bms_is_member(r, phinfo->ph_lateral))
-                   break;
-           }
-           if (lc)
-               continue;
 
            /*
             * At this stage, joininfo lists of inner and outer can contain

diff --git a/src/test/regress/expected/join.out b/src/test/regress/expected/join.out
index 2c73270143be78ef1ded9223fcf820d4ca172f0a..69427287ffdc60eaab498db32c2df6adbdc27a11 100644 (file)
--- a/src/test/regress/expected/join.out
+++ b/src/test/regress/expected/join.out
@@ -6821,20 +6821,37 @@ on true;
                            Filter: (id IS NOT NULL)
 (8 rows)
 
--- Check that SJE does not remove self joins if a PHV references the removed
--- rel laterally.
-explain (costs off)
+-- Check that PHVs do not impose any constraints on removing self joins
+explain (verbose, costs off)
 select * from emp1 t1 join emp1 t2 on t1.id = t2.id left join
     lateral (select t1.id as t1id, * from generate_series(1,1) t3) s on true;
-                    QUERY PLAN                     
----------------------------------------------------
+                        QUERY PLAN                        
+----------------------------------------------------------
  Nested Loop Left Join
-   ->  Nested Loop
-         ->  Seq Scan on emp1 t1
-         ->  Index Scan using emp1_pkey on emp1 t2
-               Index Cond: (id = t1.id)
-   ->  Function Scan on generate_series t3
-(6 rows)
+   Output: t2.id, t2.code, t2.id, t2.code, (t2.id), t3.t3
+   ->  Seq Scan on public.emp1 t2
+         Output: t2.id, t2.code
+         Filter: (t2.id IS NOT NULL)
+   ->  Function Scan on pg_catalog.generate_series t3
+         Output: t3.t3, t2.id
+         Function Call: generate_series(1, 1)
+(8 rows)
+
+explain (verbose, costs off)
+select * from generate_series(1,10) t1(id) left join
+    lateral (select t1.id as t1id, t2.id from emp1 t2 join emp1 t3 on t2.id = t3.id)
+on true;
+                      QUERY PLAN                      
+------------------------------------------------------
+ Nested Loop Left Join
+   Output: t1.id, (t1.id), t3.id
+   ->  Function Scan on pg_catalog.generate_series t1
+         Output: t1.id
+         Function Call: generate_series(1, 10)
+   ->  Seq Scan on public.emp1 t3
+         Output: t3.id, t1.id
+         Filter: (t3.id IS NOT NULL)
+(8 rows)
 
 -- We can remove the join even if we find the join can't duplicate rows and
 -- the base quals of each side are different.  In the following case we end up

diff --git a/src/test/regress/sql/join.sql b/src/test/regress/sql/join.sql
index 8a8a63bd2f1d2b60f2f643a344ebfa3437e21fef..9d6fce21ded3736731b3c0ae7b155bc046e8e937 100644 (file)
--- a/src/test/regress/sql/join.sql
+++ b/src/test/regress/sql/join.sql
@@ -2600,12 +2600,16 @@ select * from emp1 t1 left join
         on true)
 on true;
 
--- Check that SJE does not remove self joins if a PHV references the removed
--- rel laterally.
-explain (costs off)
+-- Check that PHVs do not impose any constraints on removing self joins
+explain (verbose, costs off)
 select * from emp1 t1 join emp1 t2 on t1.id = t2.id left join
     lateral (select t1.id as t1id, * from generate_series(1,1) t3) s on true;
 
+explain (verbose, costs off)
+select * from generate_series(1,10) t1(id) left join
+    lateral (select t1.id as t1id, t2.id from emp1 t2 join emp1 t3 on t2.id = t3.id)
+on true;
+
 -- We can remove the join even if we find the join can't duplicate rows and
 -- the base quals of each side are different.  In the following case we end up
 -- moving quals over to s1 to make it so it can't match any rows.