| From: | Mladen Gogala <mladen(dot)gogala(at)vmsinfo(dot)com> |
|---|---|
| To: | Bruce Momjian <bruce(at)momjian(dot)us> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, "david(at)lang(dot)hm" <david(at)lang(dot)hm>, Craig Ringer <craig(at)postnewspapers(dot)com(dot)au>, Vitalii Tymchyshyn <tivv00(at)gmail(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgreSQL(dot)org> |
| Subject: | Re: [PERFORM] Slow count(*) again... |
| Date: | 2011-02-01 23:21:04 |
| Message-ID: | 4D489560.2040107@vmsinfo.com |
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| Thread: | |
| 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
1500 Broadway
New York, NY 10036
(212) 329-5251
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