From: Tom Lane <tgl@sss.pgh.pa.us>
To: Robert Haas <robertmhaas@gmail.com>
cc: Alvaro Herrera <alvherre@2ndquadrant.com>,
        Andres Freund <andres@anarazel.de>,
        Thomas Munro <thomas.munro@enterprisedb.com>,
        Dilip Kumar <dilipbalaut@gmail.com>,
        Pg Hackers <pgsql-hackers@postgresql.org>
Subject: Re: shared memory based stat collector (was: Sharing record typmods
 between backends)
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Comments: In-reply-to Robert Haas <robertmhaas@gmail.com>
	message dated "Mon, 14 Aug 2017 11:46:10 -0400"
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Date: Mon, 14 Aug 2017 12:16:05 -0400
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Robert Haas <robertmhaas@gmail.com> writes:
> On Sun, Aug 13, 2017 at 9:59 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> In principle we could keep the existing mechanism as a fallback.
>> Whether that's worth the trouble is debatable.  The current code
>> in initdb believes that every platform has some type of DSM support
>> (see choose_dsm_implementation).  Nobody's complained about that,
>> and it certainly works on every buildfarm animal.  So for all we know,
>> dynamic_shared_memory_type = none is broken already.

> Actually, now that you mention it, I think it *is* broken already, or
> more to the point, if you configure that value, the autovacuum
> launcher hangs up, because of the AutovacuumWorkItem stuff that Alvaro
> added.  When I just tested it, the AV launcher somehow ended up
> waiting for AutovacuumLock and I had to SIGQUIT the server to shut it
> down.

Hmm, shouldn't that be an open item for v10?

> ... If somebody has a system where no other form of shared
> memory, works dynamic_shared_memory_type = mmap is still a thing, so
> the use case for "none" seems very thin indeed.  I'd vote for just
> ripping it out in v11.

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.

 dsm_type  | critters_reporting 
-----------+--------------------
 posix     |                 69
 sysv      |                 13
 windows\r |                 10
(3 rows)

			regards, tom lane


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