Re: Proposal for CSN based snapshots

On 08/22/2016 08:38 PM, Andres Freund wrote:
> On 2016-08-22 20:32:42 +0300, Heikki Linnakangas wrote:
>> I
>> remember seeing ProcArrayLock contention very visible earlier, but I can't
>> hit that now. I suspect you'd still see contention on bigger hardware,
>> though, my laptop has oly 4 cores. I'll have to find a real server for the
>> next round of testing.
>
> Yea, I think that's true. I can just about see ProcArrayLock contention
> on my more powerful laptop, to see it really bad you need bigger
> hardware / higher concurrency.

As soon as I sent my previous post, Vladimir Borodin kindly offered
access to a 32-core server for performance testing. Thanks Vladimir!

I installed Greg Smith's pgbench-tools kit on that server, and ran some
tests. I'm seeing some benefit on "pgbench -N" workload, but only after
modifying the test script to use "-M prepared", and using Unix domain
sockets instead of TCP to connect. Apparently those things add enough
overhead to mask out the little difference.

Attached is a graph with the results. Full results are available at
https://hlinnaka.iki.fi/temp/csn-4-results/. In short, the patch
improved throughput, measured in TPS, with >= 32 or so clients. The
biggest difference was with 44 clients, which saw about 5% improvement.

So, not phenomenal, but it's something. I suspect that with more cores,
the difference would become more clear.

Like on a cue, Alexander Korotkov just offered access to a 72-core
system :-). Thanks! I'll run the same tests on that.

- Heikki