Re: WIP/PoC for parallel backup

On Thu, Apr 30, 2020 at 4:15 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>
> On Wed, Apr 29, 2020 at 6:11 PM Suraj Kharage
> <suraj(dot)kharage(at)enterprisedb(dot)com> wrote:
> >
> > Hi,
> >
> > We at EnterpriseDB did some performance testing around this parallel backup to check how this is beneficial and below are the results. In this testing, we run the backup -
> > 1) Without Asif’s patch
> > 2) With Asif’s patch and combination of workers 1,2,4,8.
> >
> > We run those test on two setup
> >
> > 1) Client and Server both on the same machine (Local backups)
> >
> > 2) Client and server on a different machine (remote backups)
> >
> >
> > Machine details:
> >
> > 1: Server (on which local backups performed and used as server for remote backups)
> >
> > 2: Client (Used as a client for remote backups)
> >
> >
> ...
> >
> >
> > Client & Server on the same machine, the result shows around 50% improvement in parallel run with worker 4 and 8. We don’t see the huge performance improvement with more workers been added.
> >
> >
> > Whereas, when the client and server on a different machine, we don’t see any major benefit in performance. This testing result matches the testing results posted by David Zhang up thread.
> >
> >
> >
> > We ran the test for 100GB backup with parallel worker 4 to see the CPU usage and other information. What we noticed is that server is consuming the CPU almost 100% whole the time and pg_stat_activity shows that server is busy with ClientWrite most of the time.
> >
> >
>
> Was this for a setup where the client and server were on the same
> machine or where the client was on a different machine? If it was for
> the case where both are on the same machine, then ideally, we should
> see ClientRead events in a similar proportion?
>

During an offlist discussion with Robert, he pointed out that current
basebackup's code doesn't account for the wait event for the reading
of files which can change what pg_stat_activity shows? Can you please
apply his latest patch to improve basebackup.c's code [1] which will
take care of that waitevent before getting the data again?

[1] - https://www.postgresql.org/message-id/CA%2BTgmobBw-3573vMosGj06r72ajHsYeKtksT_oTxH8XvTL7DxA%40mail.gmail.com

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