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Re: ALTER TABLE SET STATISTICS requires AccessExclusiveLock

From: Bruce Momjian <bruce(at)momjian(dot)us>
To: Peter Eisentraut <peter_e(at)gmx(dot)net>
Cc: Simon Riggs <simon(at)2ndQuadrant(dot)com>, Alvaro Herrera <alvherre(at)commandprompt(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: ALTER TABLE SET STATISTICS requires AccessExclusiveLock
Date: 2010-03-03 00:45:06
Message-ID: 201003030045.o230j6D20028@momjian.us (view raw or flat)
Thread:
Lists: pgsql-hackers
Peter Eisentraut wrote:
> On m?n, 2010-02-22 at 10:32 -0500, Bruce Momjian wrote:
> > Simon Riggs wrote:
> > > On Mon, 2009-10-19 at 12:56 -0300, Alvaro Herrera wrote:
> > > > Simon Riggs wrote:
> > > > > 
> > > > > On Fri, 2009-08-07 at 15:58 -0400, Alvaro Herrera wrote:
> > > > > > Tom Lane wrote:
> > > > > > > Peter Eisentraut <peter_e(at)gmx(dot)net> writes:
> > > > > > > > Is there a good reason for $subject, other than that the code is entangled 
> > > > > > > > with other ALTER TABLE code?
> > > > > > > 
> > > > > > > I think it could be lower, but it would take nontrivial restructuring of
> > > > > > > the ALTER TABLE support.  In particular, consider what happens when you
> > > > > > > have a list of subcommands that don't all require the same lock level.
> > > > > > > I think you'd need to scan the list and find the highest required lock
> > > > > > > level before starting ...
> > > > > > 
> > > > > > IIRC there was a patch from Simon to address this issue, but it had some
> > > > > > holes which he didn't have time to close, so it sank.  Maybe this can be
> > > > > > resurrected and fixed.
> > > > > 
> > > > > I was intending to finish that patch in this release cycle.
> > > > 
> > > > Since you're busy with Hot Standby, any chance you could pass it on?
> > > 
> > > If you'd like. It's mostly finished, just one last thing to finish:
> > > atomic changes to pg_class via an already agreed API.
> > 
> > I assume this did not get done for 9.0.  Do we want a TODO item?
> 
> Yes.

Added:

	Reduce locking required for ALTER commands
	
	    * http://archives.postgresql.org/pgsql-hackers/2009-08/msg00533.php
	    * http://archives.postgresql.org/pgsql-hackers/2009-10/msg01083.php
	    * http://archives.postgresql.org/pgsql-hackers/2010-01/msg02349.php 

-- 
  Bruce Momjian  <bruce(at)momjian(dot)us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

  PG East:  http://www.enterprisedb.com/community/nav-pg-east-2010.do

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