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
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
