Stephan Szabo wrote:
On Mon, 13 Jan 2003, Andrew Biagioni wrote:
It appears to me that the Deadlock Checker doesn't see (and thus
release) foreign-key-based locks (see below for details). Am I missing
something? Is there a configuration item I am unaware of?
We're going to need a runnable example, I'm not 100% sure which tables
are referencing which other tables and how given the text below. I have
gotten deadlock messages from the foreign keys in the past though.
I tried to create a runnable example, and as it turns out I can't reproduce the problem in a proof-of-concept configuration. I'll have to do some more homework to determine the REAL scenario in which my problem occurs (and thus, the real cause of the problem).
HOWEVER, if I have a foreign-key-related lock, as follows, it is not
recognized:
Thread A: BEGIN WORK; UPDATE [table A, row W] /* This has a foreign key into table F, row P */
Thread B: BEGIN WORK; UPDATE [table B, row Y] /* This has a foreign key into table G, row Q */
Thread A: UPDATE [table B, row Z] /* This has a foreign key into table F, row P */
Thread B: UPDATE [table A, row X] /* This has a foreign key into table G, row Q */
Note that none of the UPDATEs step on the same actual row of the same
table, but they step (and lock) the same rows in the same tables via
foreign keys.
In this case (specifically tested), there is no deadlock detection.
Do you get a deadlock? Given the text above, I wouldn't expect one since
both transactions have the locks already when the second request for
the same lock comes in (unless you meant to swap A and B in the bottom
two).
Thanks,
Andrew
