От: Tom Lane
Тема: Re: Prefetch
Дата: ,
Msg-id: 10061.1115734580@sss.pgh.pa.us
(см: обсуждение, исходный текст)
Ответ на: Prefetch  (Matt Olson)
Список: pgsql-performance

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Prefetch  (Matt Olson, )
 Re: Prefetch  (Tom Lane, )
 Re: Prefetch  (Rod Taylor, )
 Re: Prefetch  (Greg Stark, )
  Re: Prefetch  (Matt Olson, )
  Re: Prefetch  (Tom Lane, )
 Re: Prefetch  (Sam Vilain, )
  Re: Prefetch  (Christopher Kings-Lynne, )
   Re: Prefetch  (Rod Taylor, )
   Re: Prefetch  (Bricklen Anderson, )
   Re: Prefetch  (Mischa Sandberg, )

Matt Olson <> writes:
> Other databases like Oracle and DB2 implement some sort of row prefetch.  Has
> there been serious consideration of implementing something like a prefetch
> subsystem?

No.

> Does anyone have any opinions as to why this would be a bad idea for
> postgres?

We know even less than the OS does about disk layout, and not a lot more
than it about what our next request will be.  (If we're doing a seqscan,
then of course that's not true, but I would expect the OS to be able to
figure that one out and do readahead.)

You haven't shown us your problem queries, but I think that conventional
query tuning would be a more appropriate answer.  In particular I wonder
whether you shouldn't be looking at ways to calculate multiple
aggregates in parallel.

            regards, tom lane


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