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.

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

--
Simon Riggs www.2ndQuadrant.com
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