Re: Fix background workers not restarting with restart_after_crash = on

Fujii Masao <masao.fujii@gmail.com>

From: Fujii Masao <masao.fujii@gmail.com>

To: Andrey Rudometov <unlimitedhikari@gmail.com>

Cc: pgsql-hackers@postgresql.org

Date: 2025-07-24T09:23:16Z

Lists: pgsql-hackers

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Fix background worker not restarting after crash-and-restart cycle.
- 75f633f54aaa 18.0 landed
- b5d084c5353f 19 (unreleased) landed

On Wed, Jun 11, 2025 at 5:26 PM Andrey Rudometov
<unlimitedhikari@gmail.com> wrote:
>
> Good day, hackers.
>
> Reading through changes committed in master, I noticed that after
> CleanupBackend/CleanupBackroundworker refactor background workers will fail to
> start again after postgres' restart with restart_after_crash = on.
>
> The reason is CleanupBackend and HandleChildCrash not setting background worker's
> rw_pid to zero anymore, if backend, well, crashed and failed to call shmem_exit
> and mark PMChild slot as inactive via MarkPostmasterChildInactive.
>
> Suggested solution is to finish CleanupBackend's background worker related logic
> even after treating the child process as crashed. In earlier versions zeroing of
> pids happen in HandleChildCrash anyway, so there should be no harm in doing
> the same actions here.
>
> For fast reproduction I used pg_prewarm extension, as it creates observable bgworker
> and is present in postgres tree, so tap test is easy to run.

Thanks for the report and patch! This same issue was also reported in
thread [1], where there's ongoing discussion about how to address it.

Regards,

[1] https://postgr.es/m/tencent_E00A056B3953EE6440F0F40F80EC30427D09@qq.com

-- 
Fujii Masao