Date: Sun, 24 Apr 2022 22:22:55 -0700
From: Noah Misch <noah@leadboat.com>
To: Michael Paquier <michael@paquier.xyz>
Cc: Andrey Borodin <x4mmm@yandex-team.ru>,
	Andres Freund <andres@anarazel.de>,
	Ben Chobot <bench@silentmedia.com>, Peter Geoghegan <pg@bowt.ie>,
	PostgreSQL mailing lists <pgsql-bugs@lists.postgresql.org>
Subject: Re: BUG #17401: REINDEX TABLE CONCURRENTLY creates a race condition
 on a streaming replica
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On Mon, Apr 25, 2022 at 02:11:26PM +0900, Michael Paquier wrote:
> On Sat, Apr 23, 2022 at 08:03:47PM -0700, Noah Misch wrote:
> > If this thread proceeds with the current LogAccessExclusiveLock() design, I
> > think it must include a way to disable the new behavior.  That requirement
> > would apply to any design that delays standby WAL apply in a way that
> > hot_standby_feedback can't mitigate.  We have the vacuum_truncate reloption
> > because AEL is disruptive to standby freshness.  Adding a new kind of
> > unavoidable AEL would be similarly-painful.
> 
> I am not sure that we should add more reloptions that bypass AEL
> requirements FWIW, because the standby would still be opened to cache
> errors if you don't log something, would it not?

Correct.  Even so, a mandatory AEL when replaying CIC would be worse.

> > It would nicer to fix this such that, with hot_standby_feedback, the fix
> > delays CIC on the primary instead of delaying apply on the standby.  If that's
> > too hard, AEL plus option-to-disable sounds fine.
> 
> Perhaps.  Still, that would be mostly what WaitForOlderSnapshots()
> already does, except that we'd roughly just use the limitXmin from the
> snapshot of the transaction currently running?

I don't know.