| From: | Bruce Momjian <bruce(at)momjian(dot)us> |
|---|---|
| To: | Mladen Gogala <mladen(dot)gogala(at)vmsinfo(dot)com> |
| Cc: | Greg Smith <greg(at)2ndquadrant(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Andrew Dunstan <andrew(at)dunslane(dot)net>, 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>, "pgsql-performance(at)postgresql(dot)org" <pgsql-performance(at)postgresql(dot)org> |
| Subject: | Re: [HACKERS] Slow count(*) again... |
| Date: | 2011-02-02 21:11:25 |
| Message-ID: | 201102022111.p12LBP800917@momjian.us |
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| Lists: | pgsql-hackers pgsql-performance |
Mladen Gogala wrote:
> > 2) The sort of random I/O done by index lookups can be as much as 50X as
> > expensive on standard hard drives as sequential, if every block goes to
> > physical hardware.
> >
>
> Greg, how many questions about queries not using an index have you seen?
> There is a reason why people keep asking that. The sheer number of
> questions like that on this group should tell you that there is a
> problem there.
Very few of those reports found that an index scan was indeed faster ---
they just assumed so but when they actually tested it, they understood.
--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com
+ It's impossible for everything to be true. +
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