Horton

Re: wake up logical workers after ALTER SUBSCRIPTION

Nathan Bossart <nathandbossart@gmail.com>

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From: Nathan Bossart <nathandbossart@gmail.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Melih Mutlu <m.melihmutlu@gmail.com>, Thomas Munro <thomas.munro@gmail.com>, "Hayato Kuroda (Fujitsu)" <kuroda.hayato@fujitsu.com>, "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Date: 2022-12-14T18:37:59Z
Lists: pgsql-hackers 
On Wed, Dec 14, 2022 at 01:23:18PM -0500, Tom Lane wrote:
> Nathan Bossart <nathandbossart@gmail.com> writes:
>> I'm reasonably certain the launcher is already signaled like you describe.
>> It'll just wait to start new workers if it's been less than
>> wal_retrieve_retry_interval milliseconds since the last time it started
>> workers.
> 
> Oh.  What in the world is the rationale for that?

My assumption is that this is meant to avoid starting workers as fast as
possible if they repeatedly crash.  I didn't see much discussion in the
original logical replication thread [0], but I do see follow-up discussion
about creating a separate GUC for this [1] [2].

[0] https://postgr.es/m/b8132323-b577-428c-b2aa-bf41a66b18e7%402ndquadrant.com
[1] https://postgr.es/m/CAD21AoAjTTGm%2BOx70b2OGWvb77vPcRdYeRv3gkAWx76nXDo%2BEA%40mail.gmail.com
[2] https://postgr.es/m/CAD21AoDCnyRJDUY%3DESVVe68AukvOP2dFomTeBFpAd1TiFbjsGg%40mail.gmail.com

-- 
Nathan Bossart
Amazon Web Services: https://aws.amazon.com

Commits

  1. Avoid type cheats for invalid dsa_handles and dshash_table_handles.

  2. Track logrep apply workers' last start times to avoid useless waits.

  3. Check for two_phase change at end of process_syncing_tables_for_apply.

  4. Wake up a subscription's replication worker processes after DDL.