From: Josh Berkus <josh@agliodbs.com>
To: pgsql-performance@postgresql.org
Subject: Re: Where does data in pg_stat_user_tables come from?
Date: Mon, 13 Sep 2010 16:47:31 -0700
Message-ID: <4C8EB813.6070204@agliodbs.com> (raw)
In-Reply-To: <1284421288.28610.501.camel@jd-desktop.unknown.charter.com>
References: <4C8EAE5E.70201@agliodbs.com>
<1284421288.28610.501.camel@jd-desktop.unknown.charter.com>
On 9/13/10 4:41 PM, Joshua D. Drake wrote:
> On Mon, 2010-09-13 at 16:06 -0700, Josh Berkus wrote:
>> All,
>>
>> I've been looking at pg_stat_user_tables (in 8.3, because of a project I
>> have), and it appears that autovacuum, and only autovaccum, updates the
>> data for this view. This means that one can never have data in
>> pg_stat_user_tables which is completely up-to-date, and if autovacuum is
>> off, the view is useless.
>
> As I recall its kept in shared_buffers (in some kind of counter) and
> updated only when it is requested or when autovacuum fires. This was
> done because we used to write stats every 500ms and it was a bottleneck.
> (IIRC)
Yes, looks like it only gets updated on SELECT or on autovacuum.
Thing is, a full VACUUM ANALYZE on the database, or even just ANALYZE,
should update some of the counters. And currently it doesnt, resulting
in pg_class.reltuples often being far more up to date than
pg_stat_user_tables.n_live_tup. And frankly, no way to reconcile those
two stats.
--
-- Josh Berkus
PostgreSQL Experts Inc.
http://www.pgexperts.com
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Reply to all the recipients using the --to and --cc options:
reply via email
To: pgsql-performance@postgresql.org
Cc: josh@agliodbs.com
Subject: Re: Where does data in pg_stat_user_tables come from?
In-Reply-To: <4C8EB813.6070204@agliodbs.com>
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
This inbox is served by DDX for PostgreSQL; see mirroring instructions
for how to clone and mirror all data and code used for this inbox