Re: Very low performance on table with only 298 rows - Mailing list pgsql-sql

On Thursday 14 April 2005 13:28, Richard Huxton wrote:
> Andreas Joseph Krogh wrote:
> > nbeweb=> EXPLAIN select count(*) from onp_web_index;
> >                                  QUERY PLAN
> > -------------------------------------------------------------------------
> >---- 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=> EXPLAIN ANALYZE select count(*) from onp_web_index;
> >                                                             QUERY PLAN
> > -------------------------------------------------------------------------
> >---------------------------------------------------------- Aggregate
> > (cost=205759.52..205759.52 rows=1 width=0) (actual
> > time=179748.910..179748.913 rows=1 loops=1)
> >    ->  Seq Scan on onp_web_index  (cost=0.00..205455.41 rows=121641
> > width=0) (actual time=179735.956..179747.821 rows=298 loops=1)
> >  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
be that this table is hosed somehow? Note: I have a column of type tsvector
in there, cat it be that this column causes some unexpected trouble?

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

--
Andreas Joseph Krogh <andreak@officenet.no>
Senior Software Developer / Manager
gpg public_key: http://dev.officenet.no/~andreak/public_key.asc
------------------------+---------------------------------------------+
OfficeNet AS            | The most difficult thing in the world is to |
Hoffsveien 17           | know how to do a thing and to watch         |
PO. Box 425 Skøyen      | somebody else doing it wrong, without       |
0213 Oslo               | comment.                                    |
NORWAY                  |                                             |
Phone : +47 22 13 01 00 |                                             |
Direct: +47 22 13 10 03 |                                             |
Mobile: +47 909  56 963 |                                             |
------------------------+---------------------------------------------+