Date: Wed, 20 Aug 2025 13:32:34 +0200
From: hubert depesz lubaczewski <depesz@depesz.com>
Sender: depesz@depesz.com
To: Adrian Klaver <adrian.klaver@aklaver.com>
Cc: PostgreSQL General <pgsql-general@lists.postgresql.org>
Subject: Re: Streaming replica hangs periodically for ~ 1 second - how to
 diagnose/debug
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On Tue, Aug 19, 2025 at 11:39:03AM -0700, Adrian Klaver wrote:
> > Every now and then (usually every 3-5 minutes, but not through the whole
> > day), we see situations where every query suddently takes ~ 1 second.
> Given the subject line, what you are reporting is happening on the replica,
> correct?

Yes.

> If so where is the replica relative to the primary, in terms of network
> distance?

=$ ping -c 10 primary
reports:
10 packets transmitted, 10 received, 0% packet loss, time 9181ms
rtt min/avg/max/mdev = 0.942/0.956/0.991/0.012 ms

> Also what are the 'hardware' specifications on the replica instance?

c8g.48xlarge ec2 instance. It is arm64, 192 cores, with 384 gb of ram.

As for storage, this is relatitvely slow, because this db is rather
small:
gp3 500gb volume, with 6000 iops. At no point is IO in any way close to
limits, the whole db fits easily in ram.

Best regards,

depesz