Re: WAL prefetch

On Thu, Jun 14, 2018 at 9:23 AM, Konstantin Knizhnik
<k.knizhnik@postgrespro.ru> wrote:
> Speed of random HDD access is limited by speed of disk head movement.
> By running several IO requests in parallel we just increase probability of
> head movement, so actually parallel access to HDD may even decrease IO speed
> rather than increase it.
> In theory, given several concurrent IO requests, driver can execute them in
> optimal order, trying to minimize head movement. But if there are really
> access to random pages,
> then probability that we can win something by such optimization is very
> small.

You might be right, but I feel like I've heard previous reports of
significant speedups from prefetching on HDDs.  Perhaps I am
mis-remembering.

-- 
Robert Haas
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