Message-ID: <f3927bc3a9baf4400325b91652869907f0581c97.camel@cybertec.at>
Subject: Re: Replication Testing- How to introduce a Lag
From: Laurenz Albe <laurenz.albe@cybertec.at>
To: "Subramanian,Ramachandran" <ramachandran.subramanian@alte-leipziger.de>,
  "pgsql-novice@lists.postgresql.org"	 <pgsql-novice@lists.postgresql.org>
Date: Fri, 20 Mar 2026 08:40:43 +0100
In-Reply-To: <aadb9058660d4e10b5cee44b82458802@alte-leipziger.de>
References: <aadb9058660d4e10b5cee44b82458802@alte-leipziger.de>
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On Fri, 2026-03-20 at 06:33 +0000, Subramanian,Ramachandran wrote:
> I have set up streaming replication in a our test environment and it is w=
orking OK .
>=20
> 1. Is there a way to =C2=A0force a lag between the source and the stand-b=
y in an environment where there is NO load?

Yes, set "recovery_min_apply_delay" on the standby.

> 2. During the set up process as I was thrashing around from server to ser=
ver I received this message
>    in the stand-by if I make the standby follow a new server B after it h=
ad been following a server A.
>   =C2=A0what seems to work is, additionally clearing out the archive logs=
 dir of the standby server along
>    with the data dir, before running the pg_basebackup from the standby. =
=C2=A0I am extremely new to
>    postgres and =C2=A0I want to make sure that what I am doing is not a d=
angerous practice.
>=20
> FATAL: requested timeline 2 is not a child of this server's history

You have "recovery_timeline =3D 'latest'" on the standby, right?

Then the standby that gives you that error probably followed the original p=
rimary to
a point past where the new primary forked off timeline 1.

You need to shutdown the standby that gives you the error message and run "=
pg_rewind"
to reposition it to follow the new primary.  Prerequisite: "wal_log_hints =
=3D on" or
data checksums enabled.
Otherwise you need to rebuild the standby with a new pg_basebackup.

Yours,
Laurenz Albe