On Fri, 2004-05-21 at 14:33, Carl E. McMillin wrote:
> Scenario:
>
> SELECT ... WHERE cart_id=X FOR UPDATE
>
> IF (NOT FOUND) THEN
> BEGIN
> --Here is where nothing is locked.
> --No way to guarantee no one else will create a record before we do.
> INSERT ...
> END;
> END IF;
>
Instead, I was thinking more like:
BEGIN
SELECT ... WHERE cart_id=X FOR UPDATE
IF (NOT FOUND) THEN
--Here is where nothing is locked.
--No way to guarantee no one else will create a record before we do.
INSERT ...
ELSE
UPDATE ...
END IF;
END;
Won't that "SELECT ... FOR UPDATE" block out a concurrent access to the
same cart until the first one finishes? Of course this assumes all
concurrent accesses also try to "SELECT ... FOR UPDATE" before
inserting.
Thanks,
Jeff Davis
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