Feedback-ID: i0fe9450f:Fastmail
Date: Thu, 9 Jan 2025 13:53:48 +0900
From: Michael Paquier <michael@paquier.xyz>
To: Andres Freund <andres@anarazel.de>
Cc: Postgres hackers <pgsql-hackers@lists.postgresql.org>, lukas@fittl.com
Subject: Re: WAL-logging facility for pgstats kinds
Message-ID: <Z39WXDupHUl4GLWy@paquier.xyz>
References: <Z24fyb3ipXKR38oS@paquier.xyz>
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On Thu, Jan 02, 2025 at 08:08:42PM -0500, Andres Freund wrote:
> I can't think of a real case where we would want to WAL log the stats
> themselves, rather than re-emitting stats during replay based on the WAL
> record of the "underlying object".
>=20
> Do you have counter-examples?

I'm not sure if the rebuild based on the WAL records is simpler than
logging a snapshot of them that the startup process could digest.

Anyway, I've also wanted to be able to replicate stats for historical
tracking for stats logged through hooks, and a second case was
injection point stats.  All these would require registering a custom
rmgr on top of a custom stats kind, and centralizing the logic eases a
lot some of the sanity checks they'd require as the redo callback of a
stats kind can just be attached to its PgStat_KindInfo.

I know that Lucas has been playing a bit with the area, and perhaps
he has more cases in mind where the replication of stats data could be
relevant.  So I am adding him in CC.  Perhaps I could be wrong, of
course.
--
Michael

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