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Re: ALTER TABLE SET STATISTICS requires AccessExclusiveLock

From: Simon Riggs <simon(at)2ndQuadrant(dot)com>
To: Peter Eisentraut <peter_e(at)gmx(dot)net>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: ALTER TABLE SET STATISTICS requires AccessExclusiveLock
Date: 2010-07-28 15:19:59
Message-ID: 1280330399.1878.5968.camel@ebony (view raw, whole thread or download thread mbox)
Lists: pgsql-hackers
On Wed, 2010-07-28 at 15:24 +0300, Peter Eisentraut wrote:
> On tor, 2010-07-15 at 10:24 +0100, Simon Riggs wrote:
> > Patch to reduce lock levels for 
> Tried this out, but $subject is still the case.  The problem is that
> ATRewriteCatalogs() calls AlterTableCreateToastTable() based on what it
> thinks the subcommands are, and AlterTableCreateToastTable() takes an
> AccessExclusiveLock.
> This could possibly be addressed by moving AT_SetStatistics to
> AT_PASS_MISC in order to avoid the TOAST table call.
> In a related matter, assigning ShareUpdateExclusiveLock to AT_SetStorage
> doesn't work either, because the TOAST table call needs to be done in
> that case.
> Perhaps this logic needs to be refactored a bit more so that there
> aren't any inconsistencies between the lock modes and the "passes",
> which could lead to false expectations and deadlocks.

Changes as suggested, plus tests to confirm lock levels for
ShareUpdateExclusiveLock changes. Will commit soon, if no objection.

 Simon Riggs 
 PostgreSQL Development, 24x7 Support, Training and Services

Attachment: ddl_lock_tests.patch
Description: text/x-patch (9.9 KB)

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