Re: ADD FOREIGN KEY locking

Oh,

I've just noticed something in the Commit fest post

- Reducing lock strength of trigger and foreign key DDL

Perhaps I just need to be more patient.

Cheers,

James Sewell,
Solutions Architect
______________________________________

Level 2, 50 Queen St, Melbourne VIC 3000

*P *(+61) 3 8370 8000 *W* www.lisasoft.com *F *(+61) 3 8370 8099

On Wed, Feb 18, 2015 at 10:57 AM, James Sewell <james(dot)sewell(at)lisasoft(dot)com>
wrote:

> Hello all,
>
> When I add a FK with a statement like this:
>
> ALTER TABLE a ADD FOREIGN KEY (id) REFERENCES b(id);
>
> I see a lock on table b:
>
> select locktype,mode,granted from pg_locks, pg_stat_activity where
> relation::regclass::text = 'b' AND pg_locks.pid = pg_stat_activity.pid;
>
> locktype | relation
> mode | AccessShareLock
> granted | t
> query | SOME LONG RUNNING QUERY WHICH SELECTS FROM b
>
> locktype | relation
> mode | AccessExclusiveLock
> granted | f
> query | ALTER TABLE a ADD FOREIGN KEY (id) REFERENCES b(id);
>
>
> This means that my add key won't complete until my long running query
> does. That seems a bit odd to me? In this database there are lots of
> datawarehouse type queries running, which makes it a bit hard for me to
> schedule this operation.
>
> Is this just a manifestation of adding the key being in an ALTER TABLE,
> which always needs an AccessExclusiveLock? Or am I missing some edge case
> when this lock would be required in this circumstance?
>
> No real urgency on this question, I just found it a bit strange and
> thought someone might be able to shed some light.
>
> James Sewell,
> Solutions Architect
> ______________________________________
>
>
> Level 2, 50 Queen St, Melbourne VIC 3000
>
> *P *(+61) 3 8370 8000 *W* www.lisasoft.com *F *(+61) 3 8370 8099
>
>

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