Hello Bruce Yes, transaction T1 can block a row and transaction T2 will wait. But if transaction T2 blocks a row then transaction T1 can not wait and dead.
Greetings. Walter. On Thu, Dec 25, 2014 at 7:27 AM, brucedickin...@wp.pl [firebird-support] < firebird-support@yahoogroups.com> wrote: > > > Walter, > > thank you very much for trying to explain that to me. Unfortunately I've > got lost somewhere in the middle of your response... > > >>- If you are updating or deleting just one row, then no conflict can > happen with your settings. But if you want >>to update or delete several > rows then conflicts can happens. > > In my test case I have two threads (or applications, I do not think that > does have matter) which are constantly updating the same row. > > >>- Transaction T1 starts, transaction T2 starts, transaction T1 wants to > update some rows, transaction T2 >>wants to update some different rows. No > problems until now. > > This is not my case because my transactions are working on the same row > but so far I understand that, and I agree with you. Different rows, no > deadlock should happen. > > >>Transaction T2 wants to update (and therefore blocks) a row and after > that transaction T1 wants to update >>that row. Deadlock because > transaction T1 is older than transaction T2. > > I do not understand, why deadlock? Why T1 does not wait for T2 to > commit/rollback? > > >>If transaction T1 blocks a row and after that transaction T2 wants to > update that row then transaction T2 will >>wait. But if transaction T2 > blocks a row and after that transaction T1 wants to update that row will > have a >>deadlock. > > I do not understand this, why there will be a deadlock? Because the older > transaction could not be first to block the row? > > I thought I've had all figured out:( > > > > >
