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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 933848d16d
commit ac04aa84a7
3 changed files with 61 additions and 0 deletions
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6
src/backend/optimizer/plan/planner.c
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@ -342,6 +342,11 @@ standard_planner(Query *parse, const char *query_string, int cursorOptions,
* we want to allow parallel inserts in general; updates and deletes 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
* parallel worker. We might eventually be able to relax this
* restriction, but for now it seems best not to have parallel workers
@ -352,6 +357,7 @@ standard_planner(Query *parse, const char *query_string, int cursorOptions,
parse->commandType == CMD_SELECT &&
!parse->hasModifyingCTE &&
max_parallel_workers_per_gather > 0 &&
INTERRUPTS_CAN_BE_PROCESSED() &&
!IsParallelWorker())
{
/* all the cheap tests pass, so scan the query tree */