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Don't enter parallel mode when holding interrupts.

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Doing so caused the leader to hang in wait_event=ParallelFinish, which
required an immediate shutdown to resolve.  Back-patch to v12 (all
supported versions).

Francesco Degrassi

Discussion: https://postgr.es/m/CAC-SaSzHUKT=vZJ8MPxYdC_URPfax+yoA1hKTcF4ROz_Q6z0_Q@mail.gmail.com
This commit is contained in:
Noah Misch
2024-09-17 19:53:11 -07:00
parent cbcd4bb415
commit 884860bfc0
3 changed files with 61 additions and 0 deletions
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6
src/backend/optimizer/plan/planner.c
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@@ -333,6 +333,11 @@ standard_planner(Query *parse, const char *query_string, int cursorOptions,
* if we want to allow parallel inserts in general; updates and deletes * if we want to allow parallel inserts in general; updates and deletes
* have additional problems especially around combo CIDs.) * have additional problems especially around combo CIDs.)
* *
* We don't try to use parallel mode unless interruptible. The leader
* expects ProcessInterrupts() calls to reach HandleParallelMessages().
* Even if we called HandleParallelMessages() another way, starting a
* parallel worker is too delay-prone to be prudent when uncancellable.
*
* For now, we don't try to use parallel mode if we're running inside a * For now, we don't try to use parallel mode if we're running inside a
* parallel worker. We might eventually be able to relax this * parallel worker. We might eventually be able to relax this
* restriction, but for now it seems best not to have parallel workers * restriction, but for now it seems best not to have parallel workers
@@ -343,6 +348,7 @@ standard_planner(Query *parse, const char *query_string, int cursorOptions,
parse->commandType == CMD_SELECT && parse->commandType == CMD_SELECT &&
!parse->hasModifyingCTE && !parse->hasModifyingCTE &&
max_parallel_workers_per_gather > 0 && max_parallel_workers_per_gather > 0 &&
INTERRUPTS_CAN_BE_PROCESSED() &&
!IsParallelWorker()) !IsParallelWorker())
{ {
/* all the cheap tests pass, so scan the query tree */ /* all the cheap tests pass, so scan the query tree */

24
src/test/regress/expected/select_parallel.out
View File

@@ -1252,3 +1252,27 @@ reset force_parallel_mode;
drop function set_and_report_role(); drop function set_and_report_role();
drop function set_role_and_error(int); drop function set_role_and_error(int);
drop role regress_parallel_worker; drop role regress_parallel_worker;
-- don't freeze in ParallelFinish while holding an LWLock
BEGIN;
CREATE FUNCTION my_cmp (int4, int4)
RETURNS int LANGUAGE sql AS
$$
SELECT
CASE WHEN $1 < $2 THEN -1
WHEN $1 > $2 THEN 1
ELSE 0
END;
$$;
CREATE TABLE parallel_hang (i int4);
INSERT INTO parallel_hang
(SELECT * FROM generate_series(1, 400) gs);
CREATE OPERATOR CLASS int4_custom_ops FOR TYPE int4 USING btree AS
OPERATOR 1 < (int4, int4), OPERATOR 2 <= (int4, int4),
OPERATOR 3 = (int4, int4), OPERATOR 4 >= (int4, int4),
OPERATOR 5 > (int4, int4), FUNCTION 1 my_cmp(int4, int4);
CREATE UNIQUE INDEX parallel_hang_idx
ON parallel_hang
USING btree (i int4_custom_ops);
SET force_parallel_mode = on;
DELETE FROM parallel_hang WHERE 380 <= i AND i <= 420;
ROLLBACK;

31
src/test/regress/sql/select_parallel.sql
View File

@@ -485,3 +485,34 @@ reset force_parallel_mode;
drop function set_and_report_role(); drop function set_and_report_role();
drop function set_role_and_error(int); drop function set_role_and_error(int);
drop role regress_parallel_worker; drop role regress_parallel_worker;
-- don't freeze in ParallelFinish while holding an LWLock
BEGIN;
CREATE FUNCTION my_cmp (int4, int4)
RETURNS int LANGUAGE sql AS
$$
SELECT
CASE WHEN $1 < $2 THEN -1
WHEN $1 > $2 THEN 1
ELSE 0
END;
$$;
CREATE TABLE parallel_hang (i int4);
INSERT INTO parallel_hang
(SELECT * FROM generate_series(1, 400) gs);
CREATE OPERATOR CLASS int4_custom_ops FOR TYPE int4 USING btree AS
OPERATOR 1 < (int4, int4), OPERATOR 2 <= (int4, int4),
OPERATOR 3 = (int4, int4), OPERATOR 4 >= (int4, int4),
OPERATOR 5 > (int4, int4), FUNCTION 1 my_cmp(int4, int4);
CREATE UNIQUE INDEX parallel_hang_idx
ON parallel_hang
USING btree (i int4_custom_ops);
SET force_parallel_mode = on;
DELETE FROM parallel_hang WHERE 380 <= i AND i <= 420;
ROLLBACK;