From: Tom Lane <tgl@sss.pgh.pa.us>
To: Robert Haas <robertmhaas@gmail.com>
cc: Kyotaro HORIGUCHI <horiguchi.kyotaro@lab.ntt.co.jp>,
        Sawada Masahiko <sawada.mshk@gmail.com>,
        Michael Paquier <michael.paquier@gmail.com>,
        "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Subject: Re: [HACKERS] More stats about skipped vacuums
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Comments: In-reply-to Robert Haas <robertmhaas@gmail.com>
	message dated "Wed, 07 Feb 2018 12:09:26 -0500"
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Date: Wed, 07 Feb 2018 16:59:20 -0500
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Robert Haas <robertmhaas@gmail.com> writes:
> It seems to me that there was a thread where Tom proposed removing
> support for dynamic_shared_memory_type = none.

I think you're recalling <32138.1502675970@sss.pgh.pa.us>, wherein
I pointed out that

>>> 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.

(That was in fact in the same thread Kyotaro-san just linked to about
reimplementing the stats collector.)

It's still true that we've no reason to believe there are any supported
platforms that haven't got some sort of DSM.  Performance might be a
different question, of course ... but it's hard to believe that
transferring stats through DSM wouldn't be better than writing them
out to files.

> I suggest we remove support for dynamic_shared_memory_type = none first,
> and see if we get any complaints.  If we don't, then future patches can
> rely on it being present.

If we remove it in v11, it'd still be maybe a year from now before we'd
have much confidence from that alone that nobody cares.  I think the lack
of complaints about it in 9.6 and 10 is a more useful data point.

			regards, tom lane