[infinispan-dev] Let me understand DIST

[Bela Ban]

On 3/12/12 7:13 PM, Pedro Ruivo wrote:
> On 3/10/12 5:07 PM, Bela Ban wrote:
>> If so, then I can assume that a transactional modification touching a
>> number of keys will almost always touch *all* nodes ? Example:
>> - We have 10 nodes
>> - numOwners = 2
>> - If we have a good consistent hash, I can assume that I have to modifiy
>> 5 different keys (10 / 2) on average in a TX to touch *all* nodes in the
>> cluster with the PREPARE/COMMIT phase, correct ?
>>
>> If my last statement is correct, is it safe to assume that with DIST and
>> transactional modifications, I will have a lot of TX contention /
>> collisions ?
>
> We have run experiments with ISPN 5.2 and TPC-C (1 warehouse, which
> gives a high probability of contention among transactions), and compared
> it with ISPN 5.0 (where locks were acquired on all replicas of a key,
> not only on the primary).
>
> The results running w/o write skew check and 10 nodes on our cluster
> (number of owners=2) follow:
>
>                   Tx/sec    Abort Rate
> 5.2            12         15
> 5.0            3           30
> 5.0-TOM   60         0


Excellent ! It shows that 2PC has really improved between 5.0 and 5.2...

Have you run TOM on Infinispan-5.2 / JGroups 3.1 yet ? It should 
theoretically still be 60 TXs/sec. But even compared to 12, this is 
still much better !



>>    Also, if we touch almost all nodes, would it make sense to use SEQUENCER for
>> *all* updates ? Would this obviliate the need for TOM (total order for
>> partial replication) ?
> This could be done, you are right, it's what sometimes is called
> "non-genuine" partial replication. Our take on this is that this will
> work good on small scale clusters, not on large ones.


I agree



-- 
Bela Ban, JGroups lead (http://www.jgroups.org)