Message-ID: <6ba1f723a0b6af4a1deedbe543c70ba2630b4e09.camel@cybertec.at>
Subject: Re: "not related" code blocks for removal of dead rows when using
 vacuum and this kills the performance
From: Laurenz Albe <laurenz.albe@cybertec.at>
To: Lars Aksel Opsahl <Lars.Opsahl@nibio.no>,
	"pgsql-performance@lists.postgresql.org"
	 <pgsql-performance@lists.postgresql.org>
Date: Mon, 19 Feb 2024 18:46:19 +0100
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References: 
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On Mon, 2024-02-19 at 16:14 +0000, Lars Aksel Opsahl wrote:
> Then we start testing VACUUM and very simple SQL testing in another windo=
w.
>=20
> We can now show we have performance=C2=A0of "3343.794 ms" and not "0.123 =
ms", which
> is what we get when we are able to remove dead rows and run a new analyze=
.
>=20
> The problem is that as long as the master code is active, we cannot remov=
e
> alle dead rows and that what seems to be killing the performance.
>=20
> With active I mean in hanging on pg_sleep and remember that this master h=
as
> not created the test table or inserted any data in this test table it sel=
f.
>=20
> Is the expected behavior ?

It is not entirely clear what you are doing, but it seems like you are hold=
ing
a database transaction open, and yes, then it is expected behavior that
VACUUM cannot clean up dead rows in the table.

Make sure that your database transactions are short.
Don't use table or row locks to synchronize application threads.
What you could use to synchronize your application threads are advisory loc=
ks,
they are not tied to a database transaction.

Yours,
Laurenz Albe