Horton

Re: Slow count(*) again...

Robert Haas <robertmhaas@gmail.com>

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From: Robert Haas <robertmhaas@gmail.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Mladen Gogala <mladen.gogala@vmsinfo.com>, "david@lang.hm" <david@lang.hm>, Craig Ringer <craig@postnewspapers.com.au>, Vitalii Tymchyshyn <tivv00@gmail.com>, "pgsql-performance@postgresql.org" <pgsql-performance@postgresql.org>
Date: 2010-10-13T06:45:16Z
Lists: pgsql-hackers, pgsql-performance 
On Tue, Oct 12, 2010 at 1:07 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Anyway, if anyone is hot to make COUNT(*) faster, that's where to look.
> I don't think any of the previous discussion in this thread is on-point
> at all, except for the parts where people suggested avoiding it.

I kind of hope that index-only scans help with this, too.  If you have
a wide table and a narrow (but not partial) index, and if the
visibility map bits are mostly set, it ought to be cheaper to read the
index than the table - certainly in the case where any disk I/O is
involved, and maybe even if it isn't.

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
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