Re: ALTER TABLE SET STATISTICS requires AccessExclusiveLock

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 
> >  ALTER TABLE
> >  CREATE TRIGGER
> >  CREATE RULE
> 
> 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.

Thanks for your comments. Will reconsider and update.

-- Simon Riggs           www.2ndQuadrant.comPostgreSQL Development, 24x7 Support, Training and Services