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From: Greg Sabino Mullane <htamfids@gmail.com>
Date: Wed, 4 Feb 2026 11:29:07 -0500
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Subject: Re: performance impact on read replicas during heavy vacuums on
 primary
To: Dirk Krautschick <dee-kay@gmx.de>
Cc: pgsql-performance@postgresql.org
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Is this a theoretical question, or have you seen performance issues? Yes,
it is certainly possible for vacuum to affect the replica performance. More
vacuum activity means more WAL means more WAL replay on the replica, using
up CPU and I/O. In most real-world cases, this will not be a problem, as
the replica should be able to keep up quite well even for near-constant
vacuum activity. You would need a very high WAL volume and a very
underprovisioned replica before seeing any ill effects. There are plenty of
other performance bottlenecks that will likely hit you before this one.


Cheers,
Greg

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<div dir=3D"ltr">Is this a theoretical question, or have you seen performan=
ce issues? Yes, it is certainly possible for vacuum to affect the replica p=
erformance. More vacuum activity means more WAL means more WAL replay on th=
e replica, using up CPU and I/O. In most real-world cases, this will not be=
 a problem, as the replica should be able to keep up quite well even for ne=
ar-constant vacuum activity. You would need a very high WAL volume and a ve=
ry underprovisioned replica before seeing any ill effects. There are plenty=
 of other performance bottlenecks that will likely hit you before this one.=
<div><br><div><br></div><div>Cheers,</div><div>Greg</div><div>=C2=A0</div><=
/div></div>

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