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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
This commit is contained in:
Etsuro Fujita 2022-04-28 15:15:00 +09:00
parent 55b5686511
commit 5c854e7a2c
3 changed files with 106 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

66
contrib/postgres_fdw/expected/postgres_fdw.out
View File

@ -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;

13
contrib/postgres_fdw/sql/postgres_fdw.sql
View File

@ -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;

34
src/backend/optimizer/plan/createplan.c
View File

@ -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) &&
mark_async_capable_plan(plan,
if (IsA(plan, Result))
return false;
/*
* create_projection_plan() would have pulled up the subplan, so
* check the capability using the subpath.
*/
if (mark_async_capable_plan(plan,
((ProjectionPath *) path)->subpath))
return true;
return false;