Horton

Re: [PERFORM] Slow count(*) again...

Mladen Gogala <mladen.gogala@vmsinfo.com>

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From: Mladen Gogala <mladen.gogala@vmsinfo.com>
To: Bruce Momjian <bruce@momjian.us>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, "david@lang.hm" <david@lang.hm>, Craig Ringer <craig@postnewspapers.com.au>, Vitalii Tymchyshyn <tivv00@gmail.com>, PostgreSQL-development <pgsql-hackers@postgreSQL.org>
Date: 2011-02-01T23:21:04Z
Lists: pgsql-hackers, pgsql-performance 
On 2/1/2011 5:47 PM, Bruce Momjian wrote:
> Do we want a TODO about optimizing COUNT(*) to avoid aggregate
> processing overhead?
>

Definitely not.  In my opinion, and I've seen more than a few database 
designs, having count(*) is almost always an error.
If I am counting a large table like the one below,  waiting for 30 
seconds more is not going to make much of a difference.
To paraphrase Kenny Rogers, it will be time enough for counting when the 
application is done.

Timing is on.
news=> select count(*) from moreover_documents_y2011m01;
   count
----------
  20350907
(1 row)

Time: 124142.437 ms
news=>

-- 

Mladen Gogala
Sr. Oracle DBA
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