| From: | Alvaro Herrera <alvherre(at)commandprompt(dot)com> |
|---|---|
| To: | "A(dot) Kretschmer" <andreas(dot)kretschmer(at)schollglas(dot)com> |
| Cc: | pgsql-general(at)postgresql(dot)org |
| Subject: | Re: more problems with count(*) on large table |
| Date: | 2007-09-28 16:50:34 |
| Message-ID: | 20070928165034.GG18001@alvh.no-ip.org |
| Views: | Raw Message | Whole Thread | Download mbox | Resend email |
| Thread: | |
| Lists: | pgsql-general |
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.
--
Alvaro Herrera http://www.CommandPrompt.com/
The PostgreSQL Company - Command Prompt, Inc.
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