Re: [infinispan-dev] Prepare and Rollback messages order

On 31 May 2012, at 10:21, Sebastiano Peluso wrote: > Hi all, > > I have a question about the messages order guaranteed in the execution > of the 2PC for committing a transaction in Infinispan (all versions). > > In particular I have noticed that both in replication and distribution > mode the RollbackCommand command is multicast by using a priority queue. > This means that: > 1) In replication mode, the visitRollbackCommand method of the > ReplicationInterceptor class invokes the broadcastRpcCommand method on > the RpcManager by using a true value for the usePriorityQueue parameter; > 2) In distribution mode, the visitRollbackCommand method of the > DistributionInterceptor class invokes the invokeRemotely method on the > RpcManager by using a true value for the usePriorityQueue parameter. > > Therefore the JGroups' packets containing the RollbackCommand commands > will be marked with the org.jgroups.Message.OOB and will be sent and > received by means of the Jgroups' out-of-band (OOB) thread pool. > > If I'm not wrong until now, I deduce that since OBB threads don't > guarantee ordering, then it can happen that a message M2 multicast by > node N1 after it has multicast message M1, can be delivered to a node N2 > before message M1. So the sending order is M1 -> M2 and the delivery > order is M2 -> M1 [1]. yes, you're right. > If this is true as well, I can have runs in which the PreparedCommand > command of a transaction T involved in the execution of a 2PC, can be > received by a 2PC's participant node after a RollbackCommand command for > T, even if the JGroups' messages containing the PrepareCommand commands > are actually managed by means of the JGroups's regular thread pool. The rollbackCommand is only sent once the prepare execution is acknowledged. So rollback should always arrive *after* prepare: and this ordering is not enforced at jgroups level, but by the infinispan logic. > For instance, we can consider a scenario in which a transaction T > requests a commit on node N0 and N0 multicasts the T's prepare message > on a large set of nodes (e.g. 100 nodes) S={N1,...,N100}. If the lock > acquisition fails on at least one of the 100 nodes, N0 can multicasts a > rollback message without waiting for the reply of the prepare from all > the nodes in S. That's only possible if lockAcquisitionTimeout(default to 10secs) is higher than the replicationTimeout(15 secs by default). > This means that the last rollback message can be > delivered to a node in S, say N100, before the T's prepare message and > that the locks successfully acquired by N100 for T will not be released > anymore. > > Am I missing anything? > > Thanks. > > Best Regards, > > Sebastiano Peluso > > > [1] http://www.jgroups.org/manual/html/user-advanced.html > > > -- > Sebastiano Peluso, PhD student > > Department of Computer, Control and Management Engineering > Sapienza University of Rome > Via Ariosto 25, 00185, Rome, Italy > Tel. +39 06 77274108 > Webpage http://www.dis.uniroma1.it/~peluso > > Distributed Systems Group, INESC-ID > Instituto Superior Técnico > Rua Alves Redol 9, 1000-029, Lisbon, Portugal > Webpage http://www.gsd.inesc-id.pt/~peluso > > _______________________________________________ > infinispan-dev mailing list > infinispan-dev(a)lists.jboss.org > https://lists.jboss.org/mailman/listinfo/infinispan-dev _______________________________________________ infinispan-dev mailing list infinispan-dev(a)lists.jboss.org https://lists.jboss.org/mailman/listinfo/infinispan-dev