Re: Speed up Clog Access by increasing CLOG buffers

On 10/30/16 1:32 PM, Tomas Vondra wrote:
>
> Now, maybe this has nothing to do with PostgreSQL itself, but maybe it's
> some sort of CPU / OS scheduling artifact. For example, the system has
> 36 physical cores, 72 virtual ones (thanks to HT). I find it strange
> that the "good" client counts are always multiples of 72, while the
> "bad" ones fall in between.
>
> 72 = 72 * 1 (good)
> 108 = 72 * 1.5 (bad)
> 144 = 72 * 2 (good)
> 180 = 72 * 2.5 (bad)
> 216 = 72 * 3 (good)
> 252 = 72 * 3.5 (bad)
> 288 = 72 * 4 (good)
>
> So maybe this has something to do with how OS schedules the tasks, or
> maybe some internal heuristics in the CPU, or something like that.

It might be enlightening to run a series of tests that are 72*.1 or *.2
apart (say, 72, 79, 86, ..., 137, 144).
--
Jim Nasby, Data Architect, Blue Treble Consulting, Austin TX
Experts in Analytics, Data Architecture and PostgreSQL
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