On 18/09/14 15:28, Dan Berindei wrote: > > > On Thu, Sep 18, 2014 at 3:09 PM, Bela Ban <b...@redhat.com > <mailto:b...@redhat.com>> wrote: > > > > On 18/09/14 13:03, Dan Berindei wrote: > > Thanks Pedro, this looks great. > > > > However, I don't think it's ok to treat CommitCommands/Pessimistic > > PrepareCommands as RemoteLockCommands just because they may send L1 > > invalidation commands. It's true that those commands will block, but > > there's no need to wait for any other command before doing the L1 > > invalidation. In fact, the non-tx writes on backup owners, which you > > consider to be non-blocking, can also send L1 invalidation > commands (see > > L1NonTxInterceptor.invalidateL1). > > > > On the other hand, one of the good things that the remote > executor did > > was to allow queueing lots of commands with a higher topology id, > when > > one of the nodes receives the new topology much later than the > others. > > We still have to consider each TopologyAffectedCommand as potentially > > blocking and put it through the remote executor. > > > > And InvalidateL1Commands are also TopologyAffectedCommands, so > there's > > still a potential for deadlock when L1 is enabled and we have > maxThreads > > write commands blocked sending L1 invalidations and those L1 > > invalidation commands are stuck in the remote executor's queue on > > another node. And with (very) unlucky timing the remote executor > might > > not even get to create maxThreads threads before the deadlock > appears. I > > wonder if we could write a custom executor that checks what the first > > task in the queue is every second or so, and creates a bunch of new > > threads if the first task in the queue hasn't changed. > > > > You're right about the remote executor getting full as well, we're > > lacking any feedback mechanism to tell the sender to slow down, > except > > for blocking the OOB thread. > > JGroups sends credits back to the sender *after* the message has been > delivered into the application. If the application is slow in processing > the messages, or blocks for some time, then the sender will not receive > enough credits and thus also slow down, or even block. > > > > I wonder if we could tell JGroups somehow > > to discard the message from inside MessageDispatcher.handle (e.g. throw > > a DiscardMessageException), so the sender has to retransmit it > > At this point, JGroups considers the message *delivered* (as it has > passed the UNICAST or NAKACK protocols), and it won't get resent. You > cannot discard it either, as this will be a message loss. However, if > you can tolerate loss, all is fine. E.g. if you discard a topo message > with a lower ID, I don't think any harm is done in Infinispan. (?). To > discard or not, is Infinispan's decision. > The other thing is to block, but this can have an impact back into the > JGroups thread pools. > > > Right, I was hoping the message would be marked as delivered only after > Infinispan finished processing the message (i.e. when up() returns in > UNICAST/NAKACK).
No, that's not the case. JGroups is a reliable transport and works similarly to TCP: a message is considered delivered when it leaves the NAKACK or UNICAST protocols. Same for TCP: a read reads bytes available from the socket, and those bytes are considered delivered by TCP. > Perhaps we could delay sending the credits instead? When process a > message on our internal thread pool, it would be nice if we could tell > JGroups to send credits back only when we really finished processing the > message. Not nice, as this break encapsulation. This stuff is supposed to be hidden from you. But what you can do is to block the incoming thread: only when it returns will JGroups send credits back to the sender. If there are a lot of requests, then at one point the internal ISPN thread pool will have to start blocking selected threads, and possibly start discarding selected messages IMO. -- Bela Ban, JGroups lead (http://www.jgroups.org) _______________________________________________ infinispan-dev mailing list infinispan-dev@lists.jboss.org https://lists.jboss.org/mailman/listinfo/infinispan-dev