Date: Tue, 10 Nov 2020 10:39:57 +0900
From: Michael Paquier <michael@paquier.xyz>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Dmitry Dolgov <9erthalion6@gmail.com>,
	Alvaro Herrera <alvherre@2ndquadrant.com>,
	James Coleman <jtc331@gmail.com>,
	Pg Hackers <pgsql-hackers@lists.postgresql.org>
Subject: Re: remove spurious CREATE INDEX CONCURRENTLY wait
Message-ID: <20201110013957.GD1887@paquier.xyz>
References: 
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 <20200819181646.GA1559@alvherre.pgsql>
 <20200820060929.GB3730@paquier.xyz>
 <20201103181447.54ctwnfdt5wztbqn@localhost>
 <20201109154743.sij6j5ue3j673r7h@localhost>
 <20201110012826.GC1887@paquier.xyz>
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On Mon, Nov 09, 2020 at 08:32:13PM -0500, Tom Lane wrote:
> Do we really need exclusive lock on the ProcArray to make this flag
> change?  That seems pretty bad from a concurrency standpoint.

Any place where we update vacuumFlags acquires an exclusive LWLock on
ProcArrayLock.  That's held for a very short time, so IMO it won't
matter much in practice, particularly if you compare that with the
potential gains related to the existing wait phases.
--
Michael

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