From: Andreas Joseph Krogh <andreak@officenet.no>
Organization: OfficeNet AS
To: Richard Huxton <dev@archonet.com>
Subject: Re: Very low performance on table with only 298 rows
Date: Thu, 14 Apr 2005 13:53:12 +0200
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	<425E53C7.5080604@archonet.com>
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On Thursday 14 April 2005 13:28, Richard Huxton wrote:
> Andreas Joseph Krogh wrote:
> > nbeweb=3D> EXPLAIN select count(*) from onp_web_index;
> >                                  QUERY PLAN
> > -----------------------------------------------------------------------=
=2D-
> >---- Hi all.
> > I have a problem with a table which only has 298 rows in it. A select
> > count(*) takes forever and CTRL-C also takes a long time canceling the
> > query. There are only 298 rows in the table when count(*) returns. How
> > come it takes such a long time counting only 298 rows? Here is EXPLAIN
> > ANALYZE:
> >
> > nbeweb=3D> EXPLAIN ANALYZE select count(*) from onp_web_index;
> >                                                             QUERY PLAN
> > -----------------------------------------------------------------------=
=2D-
> >---------------------------------------------------------- Aggregate=20
> > (cost=3D205759.52..205759.52 rows=3D1 width=3D0) (actual
> > time=3D179748.910..179748.913 rows=3D1 loops=3D1)
> >    ->  Seq Scan on onp_web_index  (cost=3D0.00..205455.41 rows=3D121641
> > width=3D0) (actual time=3D179735.956..179747.821 rows=3D298 loops=3D1)
> >  Total runtime: 179748.993 ms
>
> Why does PG think you have 121641 rows in this table?
> How often do you vacuum it?
> How often do you analyse it?
> Does "vacuum full verbose" show a lot of dead rows being removed?
>
> I'm suspecting a *lot* of dead rows need to be removed.

I vacuum the whole database every sunday with the command:
VACUUM ANALYZE
Do I need to issue a VACUUM FULL? I've never VACUUM FULL'ed it..

I have other much larger tables which take lot less time to count(*). Cant =
it=20
be that this table is hosed somehow? Note: I have a column of type tsvector=
=20
in there, cat it be that this column causes some unexpected trouble?

I'm issuing a VACUUM FULL verbose now...

=2D-=20
Andreas Joseph Krogh <andreak@officenet.no>
Senior Software Developer / Manager
gpg public_key: http://dev.officenet.no/~andreak/public_key.asc
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