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Re: slow query performance

From: Shridhar Daithankar <shridhar_daithankar(at)myrealbox(dot)com>
To: Dave Weaver <davew(at)wsieurope(dot)com>
Cc: pgsql-general(at)postgresql(dot)org
Subject: Re: slow query performance
Date: 2003-10-30 09:26:26
Message-ID: 3FA0D942.6040802@myrealbox.com (view raw or flat)
Thread:
Lists: pgsql-general
Dave Weaver wrote:
  too optimistic?).
> 
> For instance:
>     SELECT station, air_temp FROM obs
>          WHERE station = 'EGBB'
>             AND valid_time > '28/8/03 00:00'
>      AND valid_time < '28/10/03 00:00'
> 
> takes 4 mins 32 secs.
> 
> An EXPLAIN of the above query says:
>   NOTICE:  QUERY PLAN:
> 
>   Index Scan using obs_pkey on obs  (cost=0.00..9.01 rows=1 width=20)
> 
> A simple "SELECT count(*) from obs" query takes around that sort of time
> too.

That is no test. Postgresql will always fetch the entire table.
> 
> I have run "vacuumdb --analyze obs", to little effect.

Check http://www.varlena.com/varlena/GeneralBits/Tidbits/perf.html for general 
tuning tips and do a vacuum full if table is updated frequently. Also reindex 
the indexes after vacuum. It will take quite some time though.

See if that helps.

  Shridhar


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