From: | Andres Freund <andres(at)2ndquadrant(dot)com> |
---|---|
To: | Bruce Momjian <bruce(at)momjian(dot)us> |
Cc: | Robert Haas <robertmhaas(at)gmail(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Greg Stark <stark(at)mit(dot)edu>, Peter Geoghegan <pg(at)heroku(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Misaligned BufferDescriptors causing major performance problems on AMD |
Date: | 2014-04-17 09:23:24 |
Message-ID: | 20140417092324.GV17874@awork2.anarazel.de |
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Thread: | |
Lists: | pgsql-hackers |
On 2014-04-16 19:18:02 -0400, Bruce Momjian wrote:
> On Thu, Feb 6, 2014 at 09:40:32AM +0100, Andres Freund wrote:
> > On 2014-02-05 12:36:42 -0500, Robert Haas wrote:
> > > >> It may well be that your proposal is spot on. But I'd like to see some
> > > >> data-structure-by-data-structure measurements, rather than assuming that
> > > >> alignment must be a good thing.
> > > >
> > > > I am fine with just aligning BufferDescriptors properly. That has
> > > > clearly shown massive improvements.
> > >
> > > I thought your previous idea of increasing BUFFERALIGN to 64 bytes had
> > > a lot to recommend it.
> >
> > Good.
> >
> > I wonder if we shouldn't move that bit of logic:
> > if (size >= BUFSIZ)
> > newStart = BUFFERALIGN(newStart);
> > out of ShmemAlloc() and instead have a ShmemAllocAligned() and
> > ShmemInitStructAligned() that does it. So we can sensibly can control it
> > per struct.
> >
> > > But that doesn't mean it doesn't need testing.
> >
> > I feel the need here, to say that I never said it doesn't need testing
> > and never thought it didn't...
>
> Where are we on this?
It needs somebody with time to evaluate possible performance regressions
- I personally won't have time to look into this in detail before pgcon.
Greetings,
Andres Freund
--
Andres Freund http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
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