Date: Wed, 29 May 2024 07:18:53 +0200
From: Johannes Truschnigg <johannes@truschnigg.info>
To: Ron Johnson <ronljohnsonjr@gmail.com>
Cc: Pgsql-admin <pgsql-admin@lists.postgresql.org>
Subject: Re: Postgresql 9.5: Streaming Replication: Secondaries Fail To Start
 Post WAL Error
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On Tue, May 28, 2024 at 05:24:56PM -0400, Ron Johnson wrote:
> On Tue, May 28, 2024 at 3:11=E2=80=AFPM Johannes Truschnigg <
> >[...]
> > Yes, replication slots can interrupt your primary.
> >
>=20
> Please define "interrupt".  Using a replication slot, I thought files wou=
ld
> just accumulate in pg_wal while the replica is down (or the network is
> slow, or the replica can't keep up with the primary).
>=20
> Disaster, of course, when that disk fills up, but that's always been the
> case.

And that is exactly the scenario I meant when I said "interrupt". If you use
replication slots, your monitoring/alerting isn't set up correctly, and you=
're
accumulating a lot of WAL, chances are ENOSPC on the primary is around the
corner for you.

That's why I generally prefer a WAL archive on a separate file system for
replicas to source segments from, because filling that up won't break the
primary (unless the archive_command misbehaves). That also needs proper
monitoring/alerting, of course (and a contingency plan for what to do when/=
if
the archive runs over) - but everyone whose workload is important enough fo=
r a
replication setup to make sense is required to have that in my book.

--=20
with best regards:
- Johannes Truschnigg ( johannes@truschnigg.info )

www:   https://johannes.truschnigg.info/

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