On Tue, Oct 22, 2019 at 11:01:48AM +0530, Dilip Kumar wrote:
On Tue, Oct 22, 2019 at 10:46 AM Amit Kapila <amit.kapil...@gmail.com> wrote:
On Thu, Oct 3, 2019 at 1:18 PM Dilip Kumar <dilipbal...@gmail.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.
Yeah, That time, I was planning to compare spill vs bgworker.
Also, how about
running these tests over a network (means master and subscriber are
not on the same machine)?
Yeah, we should do that that will show the merit of streaming the
in-progress transactions.
Which I agree it's an interesting feature, I think we need to stop
adding more stuff to this patch series - it's already complex enough, so
making it even more (unnecessary) stuff is a distraction and will make
it harder to get anything committed. Typical "scope creep".
I think the current behavior (spill to file) is sufficient for v0 and
can be improved later - that's fine. I don't think we need to bother
with comparisons to master very much, because while it might be a bit
slower in some cases, you can always disable streaming (so if there's a
regression for your workload, you can undo that).
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?
I agree with the point. I think we might need to do some small
changes and test to see what could be the best method to handle the
streamed changes at the subscriber end.
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
I think the patch should do the simplest thing possible, i.e. what it
does today. Otherwise we'll never get it committed.
regards
--
Tomas Vondra http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
