Re: replay pause vs. standby promotion

From: Sergei Kornilov <sk(at)zsrv(dot)org>
To: Fujii Masao <masao(dot)fujii(at)oss(dot)nttdata(dot)com>, Atsushi Torikoshi <atorik(at)gmail(dot)com>
Cc: Jehan-Guillaume de Rorthais <jgdr(at)dalibo(dot)com>, "pgsql-hackers(at)lists(dot)postgresql(dot)org" <pgsql-hackers(at)lists(dot)postgresql(dot)org>
Subject: Re: replay pause vs. standby promotion
Date: 2020-03-25 10:42:56
Message-ID: 8496531585130947@vla1-2bebf6b1c06e.qloud-c.yandex.net
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Hi

>>  Could we add a few words in func.sgml to clarify the behavior? Especially for users from my example above. Something like:
>>
>>>  If a promotion is triggered while recovery is paused, the paused state ends, replay of any WAL immediately available in the archive or in pg_wal will be continued and then a promotion will be completed.
>
> This description is true if pause is requested by pg_wal_replay_pause(),
> but not if recovery target is reached and pause is requested by
> recovery_target_action=pause. In the latter case, even if there are WAL data
> avaiable in pg_wal or archive, they are not replayed, i.e., the promotion
> completes immediately. Probably we should document those two cases
> explicitly to avoid the confusion about a promotion and recovery pause?

This is description for pg_wal_replay_pause, but actually we suggest to call pg_wal_replay_resume in recovery_target_action=pause... So, I agree, we need to document both cases.

PS: I think we have inconsistent behavior here... Read wal during promotion from local pg_wal AND call restore_command, but ignore walreceiver also seems strange for my DBA hat...

regards, Sergei

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