On 8 Jul 2011, at 10:34, Galder Zamarreño wrote:
> Mircea, thx for writing this up. Some comments:
>
> It's not clear to me, at least given the examples in the wiki, how problem of
> Tx1 and Tx2 with a and b explained in the introduction is fixed by the
> solution.
>
> The problem exposed:
> "- with some right timing, during prepare time it is possible for these two
> transactions to deadlock:
> • Tx1 lock acquired on "a" @ N3
> • Tx2 lock acquired on "b" @ N4
> • Tx1 cannot progress acquiring lock on "b" @ N4, that lock is
> acquired by Tx2
> • Tx2 cannot acquire lock on "a" @ N3 as that lock is held by Tx1
> • Tx1 and Tx2 are waiting for each other => deadlock"
>
> The 'alleged'' solution?
>
> "In the example above, considering the view = {N1, N2, N3, N4} and
> incremental lock acquisition:
> • Tx1 acquires lock on a@ N3
> • Tx2 tries to acquire lock on a@ N3. It cannot acquire and waits for
> Tx1 to release it
> • Tx1 acquires locks on b@ N4, completes and releases locks
> • Tx2 acquires lock on a@ N3 and completes as well"
>
> Is the latter block supposed to show how the example in the introduction is
> fixed? If it is, it's not really doing it cos it's not explaining what
> happens to Tx2 that is trying to acquire locks on 'b'...
Tx2 acquires lock on b @ N4 after locking a@N3, I've updated the document.
>
> The diagrams and the associated explanations are confusing too. Example:
>
> "N1 first locks a@N3 (1)" -> in the diagram, (1) represents a call from N1 to
> N2
>
> "b@N4 (RPC 2)" -> That corresponds to to 5/6 arrows?
I've also updated this, thanks!
>
> On Jul 5, 2011, at 3:25 PM, Mircea Markus wrote:
>
>> Hi,
>>
>> This is the document describing the incremental optimistic locking Dan and
>> myself discussed last week:
>> http://community.jboss.org/wiki/IncrementalOptimisticLocking
>> Unless I'm missing something, this together with lock reordering[1] cover
>> 100% of the possible deadlock situations in the optimistic locking scheme[2]
>> - which is pretty awesome!
>>
>> Cheers,
>> Mircea
>>
>> [1] http://community.jboss.org/wiki/LockReorderingForAvoidingDeadlocks
>> [2] http://community.jboss.org/wiki/OptimisticLockingInInfinispan
>>
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>
> --
> Galder Zamarreño
> Sr. Software Engineer
> Infinispan, JBoss Cache
>
>
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