From 5c854e7a2c8a6cd26040e0f9949e7a4a007f6366 Mon Sep 17 00:00:00 2001
From: Etsuro Fujita <efujita@postgresql.org>
Date: Thu, 28 Apr 2022 15:15:00 +0900
Subject: [PATCH] Disable asynchronous execution if using gating Result nodes.
mark_async_capable_plan(), which is called from create_append_plan() to
determine whether subplans are async-capable, failed to take into
account that the given subplan created from a given subpath might
include a gating Result node if the subpath is a SubqueryScanPath or
ForeignPath, causing a segmentation fault there when the subplan created
from a SubqueryScanPath includes the Result node, or causing
ExecAsyncRequest() to throw an error about an unrecognized node type
when the subplan created from a ForeignPath includes the Result node,
because in the latter case the Result node was unintentionally
considered as async-capable, but we don't currently support executing
Result nodes asynchronously. Fix by modifying mark_async_capable_plan()
to disable asynchronous execution in such cases. Also, adjust code in
the ProjectionPath case in mark_async_capable_plan(), for consistency
with other cases, and adjust/improve comments there.
is_async_capable_path() added in commit 27e1f1456, which was rewritten
to mark_async_capable_plan() in a later commit, has the same issue,
causing the error at execution mentioned above, so back-patch to v14
where the aforesaid commit went in.
Per report from Justin Pryzby.
Etsuro Fujita, reviewed by Zhihong Yu and Justin Pryzby.
Discussion: https://postgr.es/m/20220408124338.GK24419%40telsasoft.com
---
.../postgres_fdw/expected/postgres_fdw.out | 66 +++++++++++++++++++
contrib/postgres_fdw/sql/postgres_fdw.sql | 13 ++++
src/backend/optimizer/plan/createplan.c | 34 ++++++++--
3 files changed, 106 insertions(+), 7 deletions(-)
diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 477de09a876..44457f930c2 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -10734,6 +10734,72 @@ SELECT * FROM result_tbl ORDER BY a;
(12 rows)
DELETE FROM result_tbl;
+-- Disable async execution if we use gating Result nodes for pseudoconstant
+-- quals
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT * FROM async_pt WHERE CURRENT_USER = SESSION_USER;
+ QUERY PLAN
+----------------------------------------------------------------
+ Append
+ -> Result
+ Output: async_pt_1.a, async_pt_1.b, async_pt_1.c
+ One-Time Filter: (CURRENT_USER = SESSION_USER)
+ -> Foreign Scan on public.async_p1 async_pt_1
+ Output: async_pt_1.a, async_pt_1.b, async_pt_1.c
+ Remote SQL: SELECT a, b, c FROM public.base_tbl1
+ -> Result
+ Output: async_pt_2.a, async_pt_2.b, async_pt_2.c
+ One-Time Filter: (CURRENT_USER = SESSION_USER)
+ -> Foreign Scan on public.async_p2 async_pt_2
+ Output: async_pt_2.a, async_pt_2.b, async_pt_2.c
+ Remote SQL: SELECT a, b, c FROM public.base_tbl2
+ -> Result
+ Output: async_pt_3.a, async_pt_3.b, async_pt_3.c
+ One-Time Filter: (CURRENT_USER = SESSION_USER)
+ -> Seq Scan on public.async_p3 async_pt_3
+ Output: async_pt_3.a, async_pt_3.b, async_pt_3.c
+(18 rows)
+
+EXPLAIN (VERBOSE, COSTS OFF)
+(SELECT * FROM async_p1 WHERE CURRENT_USER = SESSION_USER)
+UNION ALL
+(SELECT * FROM async_p2 WHERE CURRENT_USER = SESSION_USER);
+ QUERY PLAN
+----------------------------------------------------------------
+ Append
+ -> Result
+ Output: async_p1.a, async_p1.b, async_p1.c
+ One-Time Filter: (CURRENT_USER = SESSION_USER)
+ -> Foreign Scan on public.async_p1
+ Output: async_p1.a, async_p1.b, async_p1.c
+ Remote SQL: SELECT a, b, c FROM public.base_tbl1
+ -> Result
+ Output: async_p2.a, async_p2.b, async_p2.c
+ One-Time Filter: (CURRENT_USER = SESSION_USER)
+ -> Foreign Scan on public.async_p2
+ Output: async_p2.a, async_p2.b, async_p2.c
+ Remote SQL: SELECT a, b, c FROM public.base_tbl2
+(13 rows)
+
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT * FROM ((SELECT * FROM async_p1 WHERE b < 10) UNION ALL (SELECT * FROM async_p2 WHERE b < 10)) s WHERE CURRENT_USER = SESSION_USER;
+ QUERY PLAN
+---------------------------------------------------------------------------------
+ Append
+ -> Result
+ Output: async_p1.a, async_p1.b, async_p1.c
+ One-Time Filter: (CURRENT_USER = SESSION_USER)
+ -> Foreign Scan on public.async_p1
+ Output: async_p1.a, async_p1.b, async_p1.c
+ Remote SQL: SELECT a, b, c FROM public.base_tbl1 WHERE ((b < 10))
+ -> Result
+ Output: async_p2.a, async_p2.b, async_p2.c
+ One-Time Filter: (CURRENT_USER = SESSION_USER)
+ -> Foreign Scan on public.async_p2
+ Output: async_p2.a, async_p2.b, async_p2.c
+ Remote SQL: SELECT a, b, c FROM public.base_tbl2 WHERE ((b < 10))
+(13 rows)
+
-- Test that pending requests are processed properly
SET enable_mergejoin TO false;
SET enable_hashjoin TO false;
diff --git a/contrib/postgres_fdw/sql/postgres_fdw.sql b/contrib/postgres_fdw/sql/postgres_fdw.sql
index ed181dedff5..92d12120272 100644
--- a/contrib/postgres_fdw/sql/postgres_fdw.sql
+++ b/contrib/postgres_fdw/sql/postgres_fdw.sql
@@ -3410,6 +3410,19 @@ UNION ALL
SELECT * FROM result_tbl ORDER BY a;
DELETE FROM result_tbl;
+-- Disable async execution if we use gating Result nodes for pseudoconstant
+-- quals
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT * FROM async_pt WHERE CURRENT_USER = SESSION_USER;
+
+EXPLAIN (VERBOSE, COSTS OFF)
+(SELECT * FROM async_p1 WHERE CURRENT_USER = SESSION_USER)
+UNION ALL
+(SELECT * FROM async_p2 WHERE CURRENT_USER = SESSION_USER);
+
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT * FROM ((SELECT * FROM async_p1 WHERE b < 10) UNION ALL (SELECT * FROM async_p2 WHERE b < 10)) s WHERE CURRENT_USER = SESSION_USER;
+
-- Test that pending requests are processed properly
SET enable_mergejoin TO false;
SET enable_hashjoin TO false;
diff --git a/src/backend/optimizer/plan/createplan.c b/src/backend/optimizer/plan/createplan.c
index 7905bc46548..db11936efef 100644
--- a/src/backend/optimizer/plan/createplan.c
+++ b/src/backend/optimizer/plan/createplan.c
@@ -1112,9 +1112,9 @@ create_join_plan(PlannerInfo *root, JoinPath *best_path)
/*
* mark_async_capable_plan
- * Check whether a given Path node is async-capable, and if so, mark the
- * Plan node created from it as such and return true, otherwise return
- * false.
+ * Check whether the Plan node created from a Path node is async-capable,
+ * and if so, mark the Plan node as such and return true, otherwise
+ * return false.
*/
static bool
mark_async_capable_plan(Plan *plan, Path *path)
@@ -1125,6 +1125,13 @@ mark_async_capable_plan(Plan *plan, Path *path)
{
SubqueryScan *scan_plan = (SubqueryScan *) plan;
+ /*
+ * If the generated plan node includes a gating Result node,
+ * we can't execute it asynchronously.
+ */
+ if (IsA(plan, Result))
+ return false;
+
/*
* If a SubqueryScan node atop of an async-capable plan node
* is deletable, consider it as async-capable.
@@ -1139,6 +1146,13 @@ mark_async_capable_plan(Plan *plan, Path *path)
{
FdwRoutine *fdwroutine = path->parent->fdwroutine;
+ /*
+ * If the generated plan node includes a gating Result node,
+ * we can't execute it asynchronously.
+ */
+ if (IsA(plan, Result))
+ return false;
+
Assert(fdwroutine != NULL);
if (fdwroutine->IsForeignPathAsyncCapable != NULL &&
fdwroutine->IsForeignPathAsyncCapable((ForeignPath *) path))
@@ -1148,11 +1162,17 @@ mark_async_capable_plan(Plan *plan, Path *path)
case T_ProjectionPath:
/*
- * If the generated plan node doesn't include a Result node,
- * consider it as async-capable if the subpath is async-capable.
+ * If the generated plan node includes a Result node for
+ * the projection, we can't execute it asynchronously.
+ */
+ if (IsA(plan, Result))
+ return false;
+
+ /*
+ * create_projection_plan() would have pulled up the subplan, so
+ * check the capability using the subpath.
*/
- if (!IsA(plan, Result) &&
- mark_async_capable_plan(plan,
+ if (mark_async_capable_plan(plan,
((ProjectionPath *) path)->subpath))
return true;
return false;
--
2.39.5