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

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От Bruce Momjian
Тема Re: [HACKERS] Slow count(*) again...
Дата
Msg-id 201102022111.p12LBP800917@momjian.us
обсуждение исходный текст
Ответ на Re: [HACKERS] Slow count(*) again...  (Mladen Gogala <mladen.gogala@vmsinfo.com>)
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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@momjian.us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

  + It's impossible for everything to be true. +

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