From: Tom Lane <tgl@sss.pgh.pa.us>
To: Joe Miller <joe.d.miller@gmail.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: Auto ANALYZE criteria
Date: Mon, 20 Sep 2010 22:12:31 -0400
Message-ID: <21216.1285035151@sss.pgh.pa.us> (raw)
In-Reply-To: <AANLkTi=W02Lcn63qqxoP9jjQ0CJ8wZfCJkKV7fry7CP=@mail.gmail.com>
References: <AANLkTi=W02Lcn63qqxoP9jjQ0CJ8wZfCJkKV7fry7CP=@mail.gmail.com>
Joe Miller <joe.d.miller@gmail.com> writes:
> The autovacuum daemon currently uses the number of inserted and
> updated tuples to determine if it should run VACUUM ANALYZE on a
> table. Why doesnt it consider deleted tuples as well?
I think you misread the code.
Now there *is* a problem, pre-9.0, if your update pattern is such that
most or all updates are HOT updates. To quote from the 9.0 alpha
release notes:
Revise pgstat's tracking of tuple changes to
improve the reliability of decisions about when to
auto-analyze. The previous code depended on n_live_tuples +
n_dead_tuples - last_anl_tuples, where all three of these
numbers could be bad estimates from ANALYZE itself. Even
worse, in the presence of a steady flow of HOT updates and
matching HOT-tuple reclamations, auto-analyze might never
trigger at all, even if all three numbers are exactly right,
because n_dead_tuples could hold steady.
It's not clear to me if that matches your problem, though.
regards, tom lane
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To: pgsql-performance@postgresql.org
Cc: tgl@sss.pgh.pa.us, joe.d.miller@gmail.com
Subject: Re: Auto ANALYZE criteria
In-Reply-To: <21216.1285035151@sss.pgh.pa.us>
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