Re: Allow async standbys wait for sync replication

From: Nathan Bossart <nathandbossart(at)gmail(dot)com>
To: Andres Freund <andres(at)anarazel(dot)de>
Cc: Bharath Rupireddy <bharath(dot)rupireddyforpostgres(at)gmail(dot)com>, Kyotaro Horiguchi <horikyota(dot)ntt(at)gmail(dot)com>, SATYANARAYANA NARLAPURAM <satyanarlapuram(at)gmail(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>
Subject: Re: Allow async standbys wait for sync replication
Date: 2022-03-12 22:33:32
Message-ID: 20220312223332.GA921069@nathanxps13
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On Tue, Mar 08, 2022 at 06:01:23PM -0800, Andres Freund wrote:
> To me it's architecturally the completely wrong direction. We should move in
> the *other* direction, i.e. allow WAL to be sent to standbys before the
> primary has finished flushing it locally. Which requires similar
> infrastructure to what we're discussing here.

I think this is a good point. After all, WALRead() has the following

* XXX probably this should be improved to suck data directly from the
* WAL buffers when possible.

Once you have all the infrastructure for that, holding back WAL replay on
async standbys based on synchronous replication might be relatively easy.

Nathan Bossart
Amazon Web Services:

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