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From: Tom Lane <[email protected]>
To: Greg Rychlewski (LCL) <[email protected]>
Cc: David G. Johnston <[email protected]>
Cc: Stephen Froehlich <[email protected]>
Cc: [email protected] <[email protected]>
Subject: Re: [EXT] Re: Does cancelling autovacuum make you lose all the work it did?
Date: Fri, 12 Jun 2020 23:18:28 -0400
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>
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	<CAKFQuwZc7YjsLXZwMws9+wLA828RkYbiABfDtMJuqNL==F34Dg@mail.gmail.com>
	<[email protected]>
	<[email protected]>

"Greg Rychlewski (LCL)" <[email protected]> writes:
> Thanks for your reply. Regarding it being blocked, I don't think it is but I could be wrong. Both wait_event and wait_event_type are null. One thing I noticed though is that n_dead_tup in pg_stat_all_tables either stays the same or goes up. Should this be going down during the autovacuum?

No ... ongoing transactions could be creating new dead rows.  IIRC,
a vacuum won't report its removal of dead rows to the stats collector
till the very end, so what I'd expect is a big drop when it finishes.

(I am not sure offhand what happens to those stats if you cancel the
vacuum partway through --- it might report nothing, causing the
stats to be way off until the next successful vacuum.)

			regards, tom lane





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