On Thu, Jun 14, 2018 at 9:23 AM, Konstantin Knizhnik <k.knizh...@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
