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

"Alvaro Herrera" <alvherre@commandprompt.com> writes:

> 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.

What does EXPLAIN SELECT ... say?



--
  Gregory Stark
  EnterpriseDB          http://www.enterprisedb.com