Horton

RE: releasing ParallelApplyTxnHash when pa_launch_parallel_worker returns NULL

Zhijie Hou (Fujitsu) <houzj.fnst@fujitsu.com>

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From: "houzj.fnst@fujitsu.com" <houzj.fnst@fujitsu.com>
To: Ted Yu <yuzhihong@gmail.com>
Cc: "akapila@postgresql.org" <akapila@postgresql.org>, Postgres hackers <pgsql-hackers@lists.postgresql.org>
Date: 2023-01-11T02:12:40Z
Lists: pgsql-hackers 
On Wednesday, January 11, 2023 1:25 AM Ted Yu <yuzhihong@gmail.com> wrote:

> I was reading src/backend/replication/logical/applyparallelworker.c .
> In `pa_allocate_worker`, when pa_launch_parallel_worker returns NULL, I think the `ParallelApplyTxnHash` should be released.

Thanks for reporting.

ParallelApplyTxnHash is used to cache the state of streaming transactions being
applied. There could be multiple streaming transactions being applied in
parallel and their information were already saved in ParallelApplyTxnHash, so
we should not release them just because we don't have a worker available to
handle a new transaction here.

Best Regards,
Hou zj

Commits

  1. Avoid creating parallel apply state hash table unless required.