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help / color / mirror / Atom feedFrom: Sami Imseih <[email protected]>
To: Robert Haas <[email protected]>
Cc: David Rowley <[email protected]>
Cc: Nathan Bossart <[email protected]>
Cc: Robert Treat <[email protected]>
Cc: Jeremy Schneider <[email protected]>
Cc: [email protected]
Subject: Re: another autovacuum scheduling thread
Date: Mon, 24 Nov 2025 09:19:12 -0600
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<CA+TgmoZ44jzFBB4zxoXrX6iMxv7TPzv5duPe44UPpoyBBDL48g@mail.gmail.com>
> > What I have not been able to prove from my tests is that the processing
> > order of tables by autovacuum will actually make things any better or any
> > worse. My tests have been short 30 minute tests that count how many
> > vacuum cycles tables with various DML activity and sizes received.
> > I have not found much difference. I am also not sure how valuable
> > these short-duration tests are either.
>
> Yeah, I'm not sure that would be the right way to look for a benefit
> from something like this. I think that a better test scenario might
> involve figuring out how fast we can recover from a bad situation. As
> we've discussed before, if VACUUM is chronically unable to keep up
> with the workload, then the system is going to get into a very bad
> state and there's not really any help for it. But if we start to get
> into a bad situation due to some outside interference and then someone
> removes the interference, we might hope that this patch would help us
> get back on our feet more quickly.
>
> For instance, suppose that we have a database with a stale replication
> slot, so the oldest-XID value for the cluster keeps getting older and
> older. autovacuum is probably running but it can't clean anything up.
> Then at some point, the DBA realizes that bad things are happening and
> drops the replication slot. You might hope that, with the patch,
> autovacuum would do a better job getting the system back to a working
> state. If you set up some kind of test scenario, you could ask
> questions like "what is the largest age(relfrozenxid) that we observe
> in the database at any point during the test?" or "from the time the
> replication slot is dropped, how much time passes before
> age(datfrozenxid) drops to normal?" or "what is the maximum observed
> amount of bloat during the test?".
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Subject: Re: another autovacuum scheduling thread
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