From: Andres Freund <andres@anarazel.de>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Robert Haas <robertmhaas@gmail.com>
Cc: Alvaro Herrera <alvherre@2ndquadrant.com>
Cc: Thomas Munro <thomas.munro@enterprisedb.com>
Cc: Dilip Kumar <dilipbalaut@gmail.com>
Cc: Pg Hackers <pgsql-hackers@postgresql.org>
Subject: Re: shared memory based stat collector (was: Sharing record typmods between backends)
Date: Mon, 14 Aug 2017 09:36:10 -0700
Message-ID: <20170814163610.pgdzwygma2q6csi6@alap3.anarazel.de> (raw)
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On 2017-08-14 12:28:39 -0400, Tom Lane wrote:
> Robert Haas <robertmhaas@gmail.com> writes:
> > On Mon, Aug 14, 2017 at 12:16 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> >> Just FYI, the only values being reported by buildfarm animals are
> >> "posix", "sysv", and "windows". So while mmap may be a thing,
> >> it's an untested thing.
>
> > I'm pretty sure I dev-tested it before committing anything, but,
> > certainly, having ongoing BF coverage woudn't be a bad thing.
>
> Looking closer, the reason those are the only reported values is
> that those are the only possible results from initdb's
> choose_dsm_implementation(). So the real question here is whether
> "mmap" should be considered to dominate "sysv" if it's available.
No mmap isn't a good option - it's file backed mmap, rather than
anonymous mmap. To my knowledge there's no good portable way to use
anonymous mmap to share memory across processes unless established
before a fork().
> If so, why isn't choose_dsm_implementation() trying it; and if not,
> why are we carrying it?
I think the idea was that there might be platforms that require it, but
...
Greetings,
Andres Freund
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Cc: andres@anarazel.de, tgl@sss.pgh.pa.us, robertmhaas@gmail.com, alvherre@2ndquadrant.com, thomas.munro@enterprisedb.com, dilipbalaut@gmail.com
Subject: Re: shared memory based stat collector (was: Sharing record typmods between backends)
In-Reply-To: <20170814163610.pgdzwygma2q6csi6@alap3.anarazel.de>
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