Re: Should we cacheline align PGXACT?

From: Alexander Korotkov <a(dot)korotkov(at)postgrespro(dot)ru>
To: Daniel Gustafsson <daniel(at)yesql(dot)se>
Cc: David Steele <david(at)pgmasters(dot)net>, Andres Freund <andres(at)anarazel(dot)de>, Ashutosh Sharma <ashu(dot)coek88(at)gmail(dot)com>, Simon Riggs <simon(at)2ndquadrant(dot)com>, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Bernd Helmle <mailings(at)oopsware(dot)de>, Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Should we cacheline align PGXACT?
Date: 2017-09-21 09:08:52
Message-ID: CAPpHfdtUVfBjcP_DFheTD0Fm9=gAv2hdhyEJsJSqzkMbnXsOvQ@mail.gmail.com
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On Mon, Sep 18, 2017 at 12:41 PM, Daniel Gustafsson <daniel(at)yesql(dot)se> wrote:

> > On 16 Sep 2017, at 01:51, Alexander Korotkov <a(dot)korotkov(at)postgrespro(dot)ru>
> wrote:
> >
> > On Tue, Sep 5, 2017 at 2:47 PM, Daniel Gustafsson <daniel(at)yesql(dot)se
> <mailto:daniel(at)yesql(dot)se>> wrote:
> > > On 04 Apr 2017, at 14:58, David Steele <david(at)pgmasters(dot)net <mailto:
> david(at)pgmasters(dot)net>> wrote:
> > >
> > > On 4/4/17 8:55 AM, Alexander Korotkov wrote:
> > >> On Mon, Apr 3, 2017 at 9:58 PM, Andres Freund <andres(at)anarazel(dot)de
> <mailto:andres(at)anarazel(dot)de>
> > >>
> > >> I'm inclined to push this to the next CF, it seems we need a lot
> more
> > >> benchmarking here.
> > >>
> > >> No objections.
> > >
> > > This submission has been moved to CF 2017-07.
> >
> > This CF has now started (well, 201709 but that’s what was meant in
> above), can
> > we reach closure on this patch in this CF?
> >
> > During previous commitfest I come to doubts if this patch is really
> needed when same effect could be achieved by another (perhaps random)
> change of alignment. The thing I can do now is to retry my benchmark on
> current master and check what effect this patch has now.
>
> Considering this I’ll mark this as Waiting on Author, in case you come to
> conclusion that another patch is required then we’ll bump to a return
> status.
>

I've made some read-only benchmarking. There is clear win in this case.
The only point where median of master is higher than median of patched
version is 40 clients.

In this point observations are following:
master: 982432 939483 932075
pgxact-align: 913151 921300 938132
So, groups of observations form the overlapping ranges, and this anomaly
can be explained by statistical error.

I'm going to make some experiments with read-write and mixed workloads too.

------
Alexander Korotkov
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company

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