Re: WIP/PoC for parallel backup

On Tue, Apr 21, 2020 at 5:26 PM Ahsan Hadi <ahsan(dot)hadi(at)gmail(dot)com> wrote:
>
> On Tue, Apr 21, 2020 at 4:50 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>>
>> On Tue, Apr 21, 2020 at 5:18 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>> >
>> > On Tue, Apr 21, 2020 at 1:00 PM Asif Rehman <asifr(dot)rehman(at)gmail(dot)com> wrote:
>> > >
>> > > I did some tests a while back, and here are the results. The tests were done to simulate
>> > > a live database environment using pgbench.
>> > >
>> > > machine configuration used for this test:
>> > > Instance Type: t2.xlarge
>> > > Volume Type : io1
>> > > Memory (MiB) : 16384
>> > > vCPU # : 4
>> > > Architecture : X86_64
>> > > IOP : 16000
>> > > Database Size (GB) : 102
>> > >
>> > > The setup consist of 3 machines.
>> > > - one for database instances
>> > > - one for pg_basebackup client and
>> > > - one for pgbench with some parallel workers, simulating SELECT loads.
>> > >
>> > > basebackup | 4 workers | 8 Workers | 16 workers
>> > > Backup Duration(Min): 69.25 | 20.44 | 19.86 | 20.15
>> > > (pgbench running with 50 parallel client simulating SELECT load)
>> > >
>> > > Backup Duration(Min): 154.75 | 49.28 | 45.27 | 20.35
>> > > (pgbench running with 100 parallel client simulating SELECT load)
>> > >
>> >
>> > Thanks for sharing the results, these show nice speedup! However, I
>> > think we should try to find what exactly causes this speed up. If you
>> > see the recent discussion on another thread related to this topic,
>> > Andres, pointed out that he doesn't think that we can gain much by
>> > having multiple connections[1]. It might be due to some internal
>> > limitations (like small buffers) [2] due to which we are seeing these
>> > speedups. It might help if you can share the perf reports of the
>> > server-side and pg_basebackup side.
>> >
>>
>> Just to be clear, we need perf reports both with and without patch-set.
>
>
> These tests were done a while back, I think it would be good to run the benchmark again with the latest patches of parallel backup and share the results and perf reports.
>

Sounds good. I think we should also try to run the test with 1 worker
as well. The reason it will be good to see the results with 1 worker
is that we can know if the technique to send file by file as is done
in this patch is better or worse than the current HEAD code. So, it
will be good to see the results of an unpatched code, 1 worker, 2
workers, 4 workers, etc.

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