Date: Wed, 25 Mar 2020 17:12:48 -0300
From: Alvaro Herrera <alvherre@2ndquadrant.com>
To: Andres Freund <andres@anarazel.de>
Cc: James Coleman <jtc331@gmail.com>,
	pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: [DOC] Document concurrent index builds waiting on each other
Message-ID: <20200325201248.GA11538@alvherre.pgsql>
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On 2020-Mar-25, Andres Freund wrote:

> > I don't know if my approach is exactly what Andres has in mind
> 
> Not quite. I don't think it's generally correct for CIC to set
> PROC_IN_VACUUM. I'm doubtful it's the case even just for plain indexes -
> we don't want rows to be pruned away from under us. I also think we'd
> want to set such a flag during all of the CIC phases?
> 
> What I was thinking of was a new flag, with a distinct value from
> PROC_IN_VACUUM. It'd currently just be specified in the
> GetCurrentVirtualXIDs() calls in WaitForOlderSnapshots(). That'd avoid
> needing to wait for other CICs on different relations. Since CIC is not
> permitted on system tables, and CIC doesn't do DML on normal tables, it
> seems fairly obviously correct to exclude other CICs.

Hmm, that sounds more promising.

-- 
Álvaro Herrera                https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services