On 2016/06/08 23:16, Amit Langote wrote:
> On Wed, Jun 8, 2016 at 9:27 PM, Robert Haas <robertmh...@gmail.com> wrote:
>> On Tue, Jun 7, 2016 at 10:41 PM, Noah Misch <n...@leadboat.com> wrote:
>>> [Action required within 72 hours. This is a generic notification.]
>>>
>>> The above-described topic is currently a PostgreSQL 9.6 open item. Robert,
>>> since you committed the patch believed to have created it, you own this open
>>> item. If some other commit is more relevant or if this does not belong as a
>>> 9.6 open item, please let us know. Otherwise, please observe the policy on
>>> open item ownership[1] and send a status update within 72 hours of this
>>> message. Include a date for your subsequent status update. Testers may
>>> discover new open items at any time, and I want to plan to get them all
>>> fixed
>>> well in advance of shipping 9.6rc1. Consequently, I will appreciate your
>>> efforts toward speedy resolution. Thanks.
>>
>> Discussion of this issue is still ongoing. Accordingly, I intend to
>> wait until that discussion has concluded before proceeding further.
>> I'll check this thread again no later than Friday and send an update
>> by then.
>
> Ashutosh seemed OK with the latest patch.
I adjusted some comments per off-list suggestion from Ashutosh. Please
find attached the new version.
Thanks,
Amit
diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 1de0bc4..0468095 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -2202,6 +2202,36 @@ SELECT t1.c1, t2.c1 FROM (ft5 t1 JOIN v_ft5 t2 ON (t1.c1 = t2.c1)) left join (ft
Remote SQL: SELECT c1 FROM "S 1"."T 4"
(27 rows)
+-- query which introduces placeholders in the targetlist cannot be
+-- pushed down
+EXPLAIN (COSTS false, VERBOSE)
+SELECT q.a, ft2.c1 FROM (SELECT 13 as a FROM ft1 WHERE c1 = 13) q RIGHT JOIN ft2 ON (q.a = ft2.c1) WHERE ft2.c1 BETWEEN 10 AND 15;
+ QUERY PLAN
+---------------------------------------------------------------------------------------------------------------------------
+ Nested Loop Left Join
+ Output: (13), ft2.c1
+ Join Filter: (13 = ft2.c1)
+ -> Foreign Scan on public.ft2
+ Output: ft2.c1
+ Remote SQL: SELECT "C 1" FROM "S 1"."T 1" WHERE (("C 1" >= 10)) AND (("C 1" <= 15)) ORDER BY "C 1" ASC NULLS LAST
+ -> Materialize
+ Output: (13)
+ -> Foreign Scan on public.ft1
+ Output: 13
+ Remote SQL: SELECT NULL FROM "S 1"."T 1" WHERE (("C 1" = 13))
+(11 rows)
+
+SELECT q.a, ft2.c1 FROM (SELECT 13 as a FROM ft1 WHERE c1 = 13) q RIGHT JOIN ft2 ON (q.a = ft2.c1) WHERE ft2.c1 BETWEEN 10 AND 15;
+ a | c1
+----+----
+ | 10
+ | 11
+ | 12
+ 13 | 13
+ | 14
+ | 15
+(6 rows)
+
-- recreate the dropped user mapping for further tests
CREATE USER MAPPING FOR CURRENT_USER SERVER loopback;
DROP USER MAPPING FOR PUBLIC SERVER loopback;
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index 4d17272..f010124 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -3960,6 +3960,8 @@ postgresImportForeignSchema(ImportForeignSchemaStmt *stmt, Oid serverOid)
* 3) All join conditions are safe to push down
* 4) No relation has local filter (this can be relaxed for INNER JOIN, if we
* can move unpushable clauses upwards in the join tree).
+ * 5) There is no PlaceHolderVar originating at the joinrel that is being
+ * referenced elsewhere.
*/
static bool
foreign_join_ok(PlannerInfo *root, RelOptInfo *joinrel, JoinType jointype,
@@ -4036,6 +4038,25 @@ foreign_join_ok(PlannerInfo *root, RelOptInfo *joinrel, JoinType jointype,
return false;
}
+ /*
+ * Cannot push down the join if any PlaceHolderVar in its targetlist is
+ * needed elsewhere. That is so because the correct result cannot be
+ * ensured from the foreign join query with deparse code currently being
+ * unable to generate and push down subqueries. Remember that such a
+ * PHV was created when some subquery on nullable side of an outer join,
+ * with a non-nullable expression in its targetlist (wrapped in the PHV),
+ * was pulled up during the planner prep phase.
+ */
+ foreach(lc, root->placeholder_list)
+ {
+ PlaceHolderInfo *phinfo = lfirst(lc);
+ Relids relids = joinrel->relids;
+
+ if (bms_nonempty_difference(phinfo->ph_needed, relids) &&
+ bms_is_subset(phinfo->ph_eval_at, relids))
+ return false;
+ }
+
/* Save the join clauses, for later use. */
fpinfo->joinclauses = joinclauses;
diff --git a/contrib/postgres_fdw/sql/postgres_fdw.sql b/contrib/postgres_fdw/sql/postgres_fdw.sql
index 6c2b08c..5ae3d53 100644
--- a/contrib/postgres_fdw/sql/postgres_fdw.sql
+++ b/contrib/postgres_fdw/sql/postgres_fdw.sql
@@ -527,6 +527,12 @@ EXECUTE join_stmt;
EXPLAIN (COSTS false, VERBOSE)
SELECT t1.c1, t2.c1 FROM (ft5 t1 JOIN v_ft5 t2 ON (t1.c1 = t2.c1)) left join (ft5 t3 JOIN v_ft5 t4 ON (t3.c1 = t4.c1)) ON (t1.c1 = t3.c1);
+-- query which introduces placeholders in the targetlist cannot be
+-- pushed down
+EXPLAIN (COSTS false, VERBOSE)
+SELECT q.a, ft2.c1 FROM (SELECT 13 as a FROM ft1 WHERE c1 = 13) q RIGHT JOIN ft2 ON (q.a = ft2.c1) WHERE ft2.c1 BETWEEN 10 AND 15;
+SELECT q.a, ft2.c1 FROM (SELECT 13 as a FROM ft1 WHERE c1 = 13) q RIGHT JOIN ft2 ON (q.a = ft2.c1) WHERE ft2.c1 BETWEEN 10 AND 15;
+
-- recreate the dropped user mapping for further tests
CREATE USER MAPPING FOR CURRENT_USER SERVER loopback;
DROP USER MAPPING FOR PUBLIC SERVER loopback;
--
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