Re: POC: Cache data in GetSnapshotData()

On Thu, Mar 10, 2016 at 1:04 PM, Mithun Cy <mithun(dot)cy(at)enterprisedb(dot)com>
wrote:

>
>
> On Thu, Mar 3, 2016 at 11:50 PM, Robert Haas <robertmhaas(at)gmail(dot)com>
> wrote:
> >What if you apply both this and Amit's clog control log patch(es)? Maybe
> the combination of the two helps substantially more than either >one alone.
>
>
> I did the above tests along with Amit's clog patch. Machine :8 socket, 64
> core. 128 hyperthread.
>
> clients BASE ONLY CLOG CHANGES % Increase ONLY SAVE SNAPSHOT % Increase CLOG
> CHANGES + SAVE SNAPSHOT % Increase
> 64 29247.658034 30855.728835 5.4981181711 29254.532186 0.0235032562
> 32691.832776 11.7758992463
> 88 31214.305391 33313.393095 6.7247618606 32109.248609 2.8670931702
> 35433.655203 13.5173592978
> 128 30896.673949 34015.362152 10.0939285832 *** *** 34947.296355
> 13.110221549
> 256 27183.780921 31192.895437 14.7481857938 *** *** 32873.782735
> 20.9316056164
> With clog changes, perf of caching the snapshot patch improves.
>
>
This data looks promising to me and indicates that saving the snapshot has
benefits and we can see noticeable performance improvement especially once
the CLog contention gets reduced. I wonder if we should try these tests
with unlogged tables, because I suspect most of the contention after
CLogControlLock and ProcArrayLock is for WAL related locks, so you might be
able to see better gain with these patches. Do you think it makes sense to
check the performance by increasing CLOG buffers (patch for same is posted
in Speed up Clog thread [1]) as that also relieves contention on CLOG as
per the tests I have done?

[1] -
http://www.postgresql.org/message-id/CAA4eK1LMMGNQ439BUm0LcS3p0sb8S9kc-cUGU_ThNqMwA8_Tug@mail.gmail.com

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