Re: PATCH: logical_work_mem and logical streaming of large in-progress transactions

On Thu, Oct 3, 2019 at 1:18 PM Dilip Kumar <dilipbalaut(at)gmail(dot)com> wrote:
>
> I have attempted to test the performance of (Stream + Spill) vs
> (Stream + BGW pool) and I can see the similar gain what Alexey had
> shown[1].
>
> In addition to this, I have rebased the latest patchset [2] without
> the two-phase logical decoding patch set.
>
> Test results:
> I have repeated the same test as Alexy[1] for 1kk and 1kk data and
> here is my result
> Stream + Spill
> N time on master(sec) Total xact time (sec)
> 1kk 6 21
> 3kk 18 55
>
> Stream + BGW pool
> N time on master(sec) Total xact time (sec)
> 1kk 6 13
> 3kk 19 35
>

I think the test results for the master are missing. Also, how about
running these tests over a network (means master and subscriber are
not on the same machine)? In general, yours and Alexy's test results
show that there is merit by having workers applying such transactions.
OTOH, as noted above [1], we are also worried about the performance
of Rollbacks if we follow that approach. I am not sure how much we
need to worry about Rollabcks if commits are faster, but can we think
of recording the changes in memory and only write to a file if the
changes are above a certain threshold? I think that might help saving
I/O in many cases. I am not very sure if we do that how much
additional workers can help, but they might still help. I think we
need to do some tests and experiments to figure out what is the best
approach? What do you think?

Tomas, Alexey, do you have any thoughts on this matter? I think it is
important that we figure out the way to proceed in this patch.

[1] - https://www.postgresql.org/message-id/b25ce80e-f536-78c8-d5c8-a5df3e230785%40postgrespro.ru

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