Date: Wed, 12 Nov 2014 22:39:12 +0100
From: Andres Freund <andres@2ndquadrant.com>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Peter Eisentraut <peter_e@gmx.net>,
 Michael Paquier <michael.paquier@gmail.com>, Jim Nasby <jim@nasby.net>,
 PostgreSQL mailing lists <pgsql-hackers@postgresql.org>
Subject: Re: REINDEX CONCURRENTLY 2.0
Message-ID: <20141112213912.GH13473@awork2.anarazel.de>
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On 2014-11-12 16:11:58 -0500, Robert Haas wrote:
> On Wed, Nov 12, 2014 at 4:10 PM, Robert Haas <robertmhaas@gmail.com> wrote:
> > On Thu, Nov 6, 2014 at 9:50 AM, Peter Eisentraut <peter_e@gmx.net> wrote:
> >> If REINDEX cannot work without an exclusive lock, we should invent some
> >> other qualifier, like WITH FEWER LOCKS.
> >
> > What he said.

I'm unconvinced. A *short* exclusive lock (just to update two pg_class
row), still gives most of the benefits of CONCURRENTLY. Also, I do think
we can get rid of that period in the not too far away future.

> But more to the point .... why, precisely, can't this work without an
> AccessExclusiveLock?  And can't we fix that instead of setting for
> something clearly inferior?

It's nontrivial to fix, but I think we can fix it at some point. I just
think we should get the *major* part of the feature before investing
lots of time making it even better. There's *very* frequent questions
about having this. And people do really dangerous stuff (like manually
updating pg_class.relfilenode and such) to cope.

The problem is that it's very hard to avoid the wrong index's
relfilenode being used when swapping the relfilenodes between two
indexes.

Greetings,

Andres Freund

-- 
 Andres Freund	                   http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services


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