Re: Speed up Clog Access by increasing CLOG buffers

On 09/26/2016 07:16 PM, Tomas Vondra wrote:
>
> The averages (over the 10 runs, 5 minute each) look like this:
>
> 3.2.80 1 8 16 32 64 128 192
> --------------------------------------------------------------------
> granular-locking 1567 12146 26341 44188 43263 49590 15042
> no-content-lock 1567 12180 25549 43787 43675 51800 16831
> group-update 1550 12018 26121 44451 42734 51455 15504
> master 1566 12057 25457 42299 42513 42562 10462
>
> 4.5.5 1 8 16 32 64 128 192
> --------------------------------------------------------------------
> granular-locking 3018 19031 27394 29222 32032 34249 36191
> no-content-lock 2988 18871 27384 29260 32120 34456 36216
> group-update 2960 18848 26870 29025 32078 34259 35900
> master 2984 18917 26430 29065 32119 33924 35897
>
> That is:
>
> (1) The 3.2.80 performs a bit better than before, particularly for 128
> and 256 clients - I'm not sure if it's thanks to the reboots or so.
>
> (2) 4.5.5 performs measurably worse for >= 32 clients (by ~30%). That's
> a pretty significant regression, on a fairly common workload.
>

FWIW, now that I think about this, the regression is roughly in line
with my findings presented in my recent blog post:

http://blog.2ndquadrant.com/postgresql-vs-kernel-versions/

Those numbers were collected on a much smaller machine (2/4 cores only),
which might be why the difference observed on 32-core machine is much
more significant.

regards

--
Tomas Vondra http://www.2ndQuadrant.com
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