Re: Speed up Clog Access by increasing CLOG buffers

On Wed, Oct 5, 2016 at 12:05 PM, Tomas Vondra
<tomas(dot)vondra(at)2ndquadrant(dot)com> wrote:
> Hi,
>
> After collecting a lot more results from multiple kernel versions, I can
> confirm that I see a significant improvement with 128 and 192 clients,
> roughly by 30%:
>
> 64 128 192
> ------------------------------------------------
> master 62482 43181 50985
> granular-locking 61701 59611 47483
> no-content-lock 62650 59819 47895
> group-update 63702 64758 62596
>
> But I only see this with Dilip's workload, and only with pre-4.3.0 kernels
> (the results above are from kernel 3.19).
>

That appears positive.

> With 4.5.5, results for the same benchmark look like this:
>
> 64 128 192
> ------------------------------------------------
> master 35693 39822 42151
> granular-locking 35370 39409 41353
> no-content-lock 36201 39848 42407
> group-update 35697 39893 42667
>
> That seems like a fairly bad regression in kernel, although I have not
> identified the feature/commit causing it (and it's also possible the issue
> lies somewhere else, of course).
>
> With regular pgbench, I see no improvement on any kernel version. For
> example on 3.19 the results look like this:
>
> 64 128 192
> ------------------------------------------------
> master 54661 61014 59484
> granular-locking 55904 62481 60711
> no-content-lock 56182 62442 61234
> group-update 55019 61587 60485
>

Are the above results with synchronous_commit=off?

> I haven't done much more testing (e.g. with -N to eliminate collisions on
> branches) yet, let's see if it changes anything.
>

Yeah, let us see how it behaves with -N. Also, I think we could try
at higher scale factor?

--
With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com