Re: Increasing default value for effective_io_concurrency?

On Wed, Jul 3, 2019 at 11:24 AM Tomas Vondra
<tomas(dot)vondra(at)2ndquadrant(dot)com> wrote:
> Maybe. And it would probably work for the systems I used for benchmarks.
>
> It however assumes two things: (a) the storage system actually has
> spindles and (b) you know how many spindles there are. Which is becoming
> less and less safe these days - flash storage becomes pretty common, and
> even when there are spindles they are often hidden behind the veil of
> virtualization in a SAN, or something.

Yeah, that's true.

> I wonder if we might provide something like pg_test_prefetch which would
> measure performance with different values, similarly to pg_test_fsync.

That's not a bad idea, but I'm not sure if the results that we got in
a synthetic test - presumably unloaded - would be a good guide to what
to use in a production situation. Maybe it would; I'm just not sure.

--
Robert Haas
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The Enterprise PostgreSQL Company