Re: [GENERAL] more problems with count(*) on large table

am Fri, dem 28.09.2007, um 12:50:34 -0400 mailte Alvaro Herrera folgendes:
> A. Kretschmer wrote:
> > am Fri, dem 28.09.2007, um 11:56:46 -0400 mailte Mike Charnoky folgendes:
> > > Hi,
> > >
> > > I am still having problems performing a count(*) on a large table. This
> > >
> > > Now, certain count(*) queries are failing to complete for certain time
> > > ranges (I killed the query after about 24 hours). The table is indexed
> > > on a timestamp field. Here is one query that hangs:
> >
> > Again: an index can't help! Because of MVCC: 'select count(*)' without
> > WHERE-condition forces an seq. table-scan.
>
> But he does have a WHERE condition. THe problem is, probably, that the
> condition is not selective enough so the planner chooses to do a
> seqscan.

Yes, i'm sorry, i havn't recognize this. Maybe wrong statistics. As Andrew suggested, a 'ALTER TABLE...SET STATISTICS' can help.

Andreas

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Andreas Kretschmer
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