On 2010-05-11 14:29 +0200, Robert Haas wrote:
> On Tue, May 11, 2010 at 2:16 AM, Dmitry Fefelov <fozzy@ac-sw.com> wrote:
>>> The referential integrity triggers contain some extra magic that isn't
>>> easily simulatable in userland, and that is necessary to make the
>>> foreign key constraints airtight. We've discussed this previously but
>>> I don't remember which thread it was or the details of when things
>>> blow up. I think it's something like this: the parent has a tuple
>>> that is not referenced by any child. Transaction 1 begins, deletes
>>> the parent tuple (checking that it has no children), and pauses.
>>> Transaction 2 begins, adds a child tuple that references the parent
>>> tuple (checking that the parent exists, which it does), and commits.
>>> Transaction 1 commits.
>>
>> Will SELECT ... FOR SHARE not help?
>
> Try it, with the example above. I think you'll find that it doesn't.
TXA => delete from foo;
DELETE 1
TXB => select a from foo for share; -- waits
What am I missing?
Regards,
Marko Tiikkaja