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Re: Where does data in pg_stat_user_tables come from?

From: Josh Berkus <josh(at)agliodbs(dot)com>
To: pgsql-performance(at)postgresql(dot)org
Subject: Re: Where does data in pg_stat_user_tables come from?
Date: 2010-09-16 18:39:22
Message-ID: 4C92645A.1040208@agliodbs.com (view raw or flat)
Thread:
Lists: pgsql-performance
> It's been pure nonsense in this thread.  Please show an example of
> what's not working.

1) Init a postgresql 8.3 with autovacuum disabled.

2) Load a backup of a database into that PostgreSQL.

3) Check pg_stat_user_tables.  n_live_tup for all tables will be 0.

4) VACUUM ANALYZE the whole database.

5) n_live_tup will *still* be 0.  Whereas reltuples in pg_class will be
reasonable accurate.

> Um ... it updates the last_autovacuum and last_autoanalyze columns,
> but the others are not its responsibility.

Right. I'm contending that ANALYZE *should* update those columns.
Current behavior is unintuitive and makes the stats in
pg_stat_user_tables almost useless, since you can never get even
approximately a coherent snapshot of data for all tables.

-- 
                                  -- Josh Berkus
                                     PostgreSQL Experts Inc.
                                     http://www.pgexperts.com

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