Re: ALTER TABLE SET STATISTICS requires AccessExclusiveLock

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.