Re: POC: Cache data in GetSnapshotData()

On 2015-05-20 19:56:39 +0530, Amit Kapila wrote:
> I have done some tests with this patch to see the benefit with
> and it seems to me this patch helps in reducing the contention
> around ProcArrayLock, though the increase in TPS (in tpc-b tests
> is around 2~4%) is not very high.
>
> pgbench (TPC-B test)
> ./pgbench -c 64 -j 64 -T 1200 -M prepared postgres

Hm, so it's a read mostly test. I probably not that badly contended on
the snapshot acquisition itself. I'd guess a 80/20 read/write mix or so
would be more interesting for the cases where we hit this really bad.

> Without Patch (HEAD - e5f455f5) - Commit used is slightly old, but I
> don't think that matters for this test.

Agreed, shouldn't make much of a difference.

> +1 to proceed with this patch for 9.6, as I think this patch improves the
> situation with compare to current.

Yea, I think so too.

> Also I have seen crash once in below test scenario:
> Crashed in test with scale-factor - 300, other settings same as above:
> ./pgbench -c 128 -j 128 -T 1800 -M prepared postgres

The patch as is really is just a proof of concept. I wrote it during a
talk the flight back from fosdem...

Thanks for the look.

Greetings,

Andres Freund