Date: Wed, 29 Sep 2021 11:48:11 -0300
From: Alvaro Herrera <alvherre@alvh.no-ip.org>
To: Hannu Krosing <hannuk@google.com>
Cc: "Bossart, Nathan" <bossartn@amazon.com>,
	Kyotaro Horiguchi <horikyota.ntt@gmail.com>,
	"andres@anarazel.de" <andres@anarazel.de>,
	"masao.fujii@oss.nttdata.com" <masao.fujii@oss.nttdata.com>,
	"pgsql-hackers@lists.postgresql.org" <pgsql-hackers@lists.postgresql.org>,
	"mengjuan.cmj@alibaba-inc.com" <mengjuan.cmj@alibaba-inc.com>,
	"Jakub.Wartak@tomtom.com" <Jakub.Wartak@tomtom.com>,
	Ryo Matsumura <matsumura.ryo@fujitsu.com>
Subject: Re: prevent immature WAL streaming
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On 2021-Sep-24, Hannu Krosing wrote:

Hi Hannu

> In the first email you write
> 
> > As mentioned in the course of thread [1], we're missing a fix for
> streaming replication to avoid sending records that the primary hasn't
> fully flushed yet.  This patch is a first attempt at fixing that problem
> by retreating the LSN reported as FlushPtr whenever a segment is
> registered, based on the understanding that if no registration exists
> then the LogwrtResult.Flush pointer can be taken at face value; but if a
> registration exists, then we have to stream only till the start LSN of
> that registered entry.
> 
> So did we end up holding back the wal_sender to not send anything that
> is not confirmed as flushed on master

No.  We eventually realized that that approach was a dead end, so I
abandoned the whole thing and attacked the problem differently.  So your
other questions don't apply.  I tried to make the commit message explain
both the problem and the solution in as much detail as possible; please
have a look at that and let me know if something is unclear.

Thanks

-- 
Álvaro Herrera         PostgreSQL Developer  —  https://www.EnterpriseDB.com/
"El miedo atento y previsor es la madre de la seguridad" (E. Burke)