ADD FOREIGN KEY locking
Hello all,
James Sewell,
Solutions Architect
______________________________________
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 | relationmode | AccessShareLockgranted | tquery | SOME LONG RUNNING QUERY WHICH SELECTS FROM blocktype | relationmode | AccessExclusiveLockgranted | fquery | 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
______________________________________
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