Re: Improving connection scalability: GetSnapshotData()

On Sat, Mar 28, 2020 at 06:39:32PM -0700, Peter Geoghegan wrote:
> On Sun, Mar 1, 2020 at 12:36 AM Andres Freund <andres(at)anarazel(dot)de> wrote:
> > The workload is a pgbench readonly, with pgbench -M prepared -c $conns
> > -j $conns -S -n for each client count. This is on a machine with 2
> > Intel(R) Xeon(R) Platinum 8168, but virtualized.
> >
> > conns tps master tps pgxact-split
> >
> > 1 26842.492845 26524.194821
> > 10 246923.158682 249224.782661
> > 50 695956.539704 709833.746374
> > 100 1054727.043139 1903616.306028
> > 200 964795.282957 1949200.338012
> > 300 906029.377539 1927881.231478
> > 400 845696.690912 1911065.369776
> > 500 812295.222497 1926237.255856
> > 600 888030.104213 1903047.236273
> > 700 866896.532490 1886537.202142
> > 800 863407.341506 1883768.592610
> > 900 871386.608563 1874638.012128
> > 1000 887668.277133 1876402.391502
> > 1500 860051.361395 1815103.564241
> > 2000 890900.098657 1775435.271018
> > 3000 874184.980039 1653953.817997
> > 4000 845023.080703 1582582.316043
> > 5000 817100.195728 1512260.802371
> >
> > I think these are pretty nice results.
>
> This scalability improvement is clearly very significant. There is
> little question that this is a strategically important enhancement for
> the Postgres project in general. I hope that you will ultimately be
> able to commit the patchset before feature freeze.

+1

> I have heard quite a few complaints about the scalability of snapshot
> acquisition in Postgres. Generally from very large users that are not
> well represented on the mailing lists, for a variety of reasons. The
> GetSnapshotData() bottleneck is a *huge* problem for us. (As problems
> for Postgres users go, I would probably rank it second behind issues
> with VACUUM.)

+1

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Bruce Momjian <bruce(at)momjian(dot)us> https://momjian.us
EnterpriseDB https://enterprisedb.com

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