On 06/21/2012 07:43 PM, Tom Lane wrote:
> Andrew Dunstan<andrew@dunslane.net> writes:
>> On 06/21/2012 06:25 PM, Tom Lane wrote:
>>> Hm, I guess I've forgotten that one?
>> See<http://archives.postgresql.org/pgsql-hackers/2012-01/msg00561.php>
> I didn't understand that then, and I still don't. The ALTER TABLE
> CLUSTER might need exclusive lock, but it's not going to hold the lock
> long enough to be an issue. I could see that there's a problem with
> identify_locking_dependencies believing that two CONSTRAINT items
> conflict (do they really?) but not convinced the CLUSTER aspect has
> anything to do with it.
>
>
If something else holds a lock on the table (e.g. another CREATE INDEX)
the ALTER TABLE will block until it's done, waiting for an ACCESS
EXCLUSIVE lock. The whole method of operation of parallel restore is
that we are not supposed to start items that might be blocked by
currently running operations.
cheers
andrew