Date: Tue, 17 Aug 2021 18:32:08 -0400
From: "alvherre@alvh.no-ip.org" <alvherre@alvh.no-ip.org>
To: "Bossart, Nathan" <bossartn@amazon.com>
Cc: Kyotaro Horiguchi <horikyota.ntt@gmail.com>,
	"x4mmm@yandex-team.ru" <x4mmm@yandex-team.ru>,
	"a.lubennikova@postgrespro.ru" <a.lubennikova@postgrespro.ru>,
	"hlinnaka@iki.fi" <hlinnaka@iki.fi>,
	"matsumura.ryo@fujitsu.com" <matsumura.ryo@fujitsu.com>,
	"masao.fujii@gmail.com" <masao.fujii@gmail.com>,
	"pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Subject: Re: archive status ".ready" files may be created too early
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On 2021-Aug-17, Bossart, Nathan wrote:
> On 8/17/21, 2:13 PM, "alvherre@alvh.no-ip.org" <alvherre@alvh.no-ip.org> wrote:
>
> > So, why isn't it that we call Register in XLogInsertRecord, and
> > Notify in XLogWrite?
> 
> We do.  However, we also call NotifySegmentsReadyForArchive() in
> XLogInsertRecord() to handle the probably-unlikely scenario that the
> flush pointer has already advanced past the to-be-registered boundary.
> This ensures that the .ready files are created as soon as possible.

I see.

I have two thoughts on that.  First, why not do it outside the block
that tests for crossing a segment boundary?  If that's a good thing to
do, then we should do it always.

However, why do it in a WAL-producing client-connected backend?  It
strikes me as a bad thing to do, because you are possibly causing delays
for client-connected backends.  I suggest that we should give this task
to the WAL writer process -- say, have XLogBackgroundFlush do it.

-- 
Álvaro Herrera              Valdivia, Chile  —  https://www.EnterpriseDB.com/
"All rings of power are equal,
But some rings of power are more equal than others."
                                 (George Orwell's The Lord of the Rings)