Re: Speed up Clog Access by increasing CLOG buffers

On Mon, Oct 31, 2016 at 7:02 PM, Tomas Vondra
<tomas(dot)vondra(at)2ndquadrant(dot)com> wrote:
>
> The remaining benchmark with 512 clog buffers completed, and the impact
> roughly matches Dilip's benchmark - that is, increasing the number of clog
> buffers eliminates all positive impact of the patches observed on 128
> buffers. Compare these two reports:
>
> [a] http://tvondra.bitbucket.org/#pgbench-3000-logged-sync-noskip-retest
>
> [b] http://tvondra.bitbucket.org/#pgbench-3000-logged-sync-noskip-retest-512
>
> With 128 buffers the group_update and granular_locking patches achieve up to
> 50k tps, while master and no_content_lock do ~30k tps. After increasing
> number of clog buffers, we get only ~30k in all cases.
>
> I'm not sure what's causing this, whether we're hitting limits of the simple
> LRU cache used for clog buffers, or something else.
>

I have also seen previously that increasing clog buffers to 256 can
impact performance negatively. So, probably here the gains due to
group_update patch is negated due to the impact of increasing clog
buffers. I am not sure if it is good idea to see the impact of
increasing clog buffers along with this patch.

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