Date: Sat, 28 Mar 2020 21:44:02 -0400
From: Bruce Momjian <bruce@momjian.us>
To: Peter Geoghegan <pg@bowt.ie>
Cc: Andres Freund <andres@anarazel.de>,
	PostgreSQL Hackers <pgsql-hackers@postgresql.org>
Subject: Re: Improving connection scalability: GetSnapshotData()
Message-ID: <20200329014402.GA9116@momjian.us>
References: <20200301083601.ews6hz5dduc3w2se@alap3.anarazel.de>
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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@anarazel.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

-- 
  Bruce Momjian  <bruce@momjian.us>        https://momjian.us
  EnterpriseDB                             https://enterprisedb.com

+ As you are, so once was I.  As I am, so you will be. +
+                      Ancient Roman grave inscription +