Re: How is this possible "publication does not exist"

From: Andrey Borodin <x4mmm(at)yandex-team(dot)ru>
To: Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>
Cc: Peter Eisentraut <peter(dot)eisentraut(at)2ndquadrant(dot)com>, Dave Cramer <davecramer(at)gmail(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: How is this possible "publication does not exist"
Date: 2021-07-23 11:02:43
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> 20 дек. 2019 г., в 06:39, Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com> написал(а):
> While trying to reproduce this I however ran into a related issue with
> pgoutput/pg_logical_slot_get_binary_changes. If you call the function
> repeatedly (~10x) you'll get an error like this:
> FATAL: out of relcache_callback_list slots
> CONTEXT: slot "slot", output plugin "pgoutput", in the startup callback
> server closed the connection unexpectedly
> This probably means the server terminated abnormally
> before or while processing the request.
> The reason is very simple - each call executes pgoutput_startup, which
> does CacheRegisterRelcacheCallback in init_rel_sync_cache. And we do
> this on each pg_logical_slot_get_binary_changes() call and never remove
> the callbacks, so we simply run out of MAX_RELCACHE_CALLBACKS slots.
> Not sure if this is a known issue/behavior, but it seems a bit annoying
> and possibly related to the issue reported by Dave.

Sorry for bumping old thread.
I was involved in troubleshooting logical replication recently. And found out that it sometimes has a really annoying error reporting.
While source of the problem was allegedly in low max_replication_slots, users were getting only this error about relcache_callback_list.

Maybe we could fix this particular error by deduplicating callbacks?

Best regards, Andrey Borodin.

Attachment Content-Type Size
0001-Avoid-duplication-in-relcache-and-syscache-callbacks.patch application/octet-stream 2.5 KB

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