Horton

Re: Race conditions in 019_replslot_limit.pl

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Andres Freund <andres@anarazel.de>
Cc: Masahiko Sawada <sawada.mshk@gmail.com>, Kyotaro Horiguchi <horikyota.ntt@gmail.com>, hlinnaka@iki.fi, pgsql-hackers@postgresql.org
Date: 2022-02-18T23:15:21Z
Lists: pgsql-hackers 
Andres Freund <andres@anarazel.de> writes:
> On 2022-02-17 21:55:21 -0800, Andres Freund wrote:
>> Isn't it pretty bonkers that we allow error processing to get stuck behind
>> network traffic, *before* we have have released resources (locks etc)?

It's more or less intentional, per elog.c:

    /*
     * This flush is normally not necessary, since postgres.c will flush out
     * waiting data when control returns to the main loop. But it seems best
     * to leave it here, so that the client has some clue what happened if the
     * backend dies before getting back to the main loop ... error/notice
     * messages should not be a performance-critical path anyway, so an extra
     * flush won't hurt much ...
     */
    pq_flush();

Perhaps it'd be sensible to do this only in debugging (ie Assert)
builds?

			regards, tom lane

Commits

  1. Revert 019_replslot_limit.pl related debugging aids.

  2. Don't fail for > 1 walsenders in 019_replslot_limit, add debug messages.

  3. Add retries for further investigation of 019_replslot_limit.pl failures.

  4. Add further debug info to help debug 019_replslot_limit.pl failures.

  5. Add temporary debug info to help debug 019_replslot_limit.pl failures.

  6. Move replication slot release to before_shmem_exit().

  7. Server-side fix for delayed NOTIFY and SIGTERM processing.