[jboss-jira] [JBoss JIRA] (JGRP-1426) Group unable to accept new members: FLUSH stuck after MERGE_RSP timed out

[David Hotham (JIRA)]

    [ https://issues.jboss.org/browse/JGRP-1426?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12669642#comment-12669642 ] 

David Hotham commented on JGRP-1426:
------------------------------------

As I reported on the mailing list, I'm reproducing this using my full application - which I'm afraid I'm reluctant to send you.  (Besides, it's written in Scala, which you "don't do" ;-) 

If it's really essential then I can try to set up a more self-contained test, but I'm hoping that my description is clear enough that this won't be needed.  Certainly I feel as though I understand what has gone wrong in the flows (if not how to fix it!) so if I haven't convinced you then that's a failure of my communication (or I'm completely wrong).

I can certainly send you more trace from my own repro, if that would help; and I'd be happy to run with a version of JGroups that included any extra trace you want to add.

Having said that, my testcase really isn't anything more than: set up a group of four members, kill one, and restart it.  There are also some broadcast message flows from the application when it sees a change of view - I guess this probably makes it more likely that there's non-trivial flushing going on.

It seems to be quite a tough timing window to hit.  I speculate that we need to be relatively slow to recognise that old-D is dead, so that when you get the MERGE_REQ from new-D you're still doing a flush associated with losing old-D.  Certainly - as in the trace above - you need to be slow to deal with new-D's MERGE_REQ at B, so that it is timed out.

Does that all make sense?  Do let me know if I can help out any more.
                
> Group unable to accept new members: FLUSH stuck after MERGE_RSP timed out
> -------------------------------------------------------------------------
>
>                 Key: JGRP-1426
>                 URL: https://issues.jboss.org/browse/JGRP-1426
>             Project: JGroups
>          Issue Type: Bug
>    Affects Versions: 3.1
>            Reporter: David Hotham
>            Assignee: Vladimir Blagojevic
>             Fix For: 3.1
>
>
> We have two sub-groups, [B, C, A] and [D].
> (1) D sends a MERGE_REQ to B.
> 2012-02-18 22:15:03.888 [MergeTask,Clumpy Test Cluster,Member-D] TRACE org.jgroups.protocols.pbcast.Merger - Member-B: sending MERGE_REQ to [Member-D, Member-B]
> (2) B receives this.  There's some delay in processing it (I think because there's another merge or flush going on; but the exact reason doesn't matter for this issue).  When processing does start, B begins a flush.
> 2012-02-18 22:15:03.889 [OOB-2,Clumpy Test Cluster,Member-B] TRACE org.jgroups.protocols.TCP - received [dst: Member-B, src: Member-D (3 headers), size=0 bytes, flags=OOB], headers are GMS: GmsHeader[MERGE_REQ]: merge_id=Member-D::1, mbrs=[Member-B, Member-C, Member-A, Member-D], UNICAST2: DATA, seqno=1, conn_id=2, first, TCP: [channel_name=Clumpy Test Cluster]
> 2012-02-18 22:15:08.811 [OOB-2,Clumpy Test Cluster,Member-B] TRACE org.jgroups.protocols.pbcast.Merger - Member-B: got merge request from Member-D, merge_id=Member-D::1, mbrs=[Member-B, Member-A, Member-C, Member-D]
> (3) D times out waiting for the MERGE_RSP from B:
> 2012-02-18 22:15:08.889 [MergeTask,Clumpy Test Cluster,Member-D] TRACE org.jgroups.protocols.pbcast.Merger - Member-D: collected 1 merge response(s) in 5001 ms
> 2012-02-18 22:15:08.889 [MergeTask,Clumpy Test Cluster,Member-D] DEBUG org.jgroups.protocols.pbcast.Merger - merge leader Member-D did not get responses from all 2 partition coordinators; missing responses from 1 members, removing them from the merge
> (4) D completes the (failed) merge and broadcasts STOP_FLUSH:
> 2012-02-18 22:15:08.896 [MergeTask,Clumpy Test Cluster,Member-D] TRACE org.jgroups.protocols.pbcast.Merger - Member-D: received all ACKs (1) for merge view MergeView::[Member-D|1] [Member-D], subgroups=[Member-D|0] [Member-D] in 7ms
> 2012-02-18 22:15:08.896 [MergeTask,Clumpy Test Cluster,Member-D] TRACE org.jgroups.protocols.pbcast.GMS - Member-D: sending RESUME event
> 2012-02-18 22:15:08.897 [MergeTask,Clumpy Test Cluster,Member-D] DEBUG org.jgroups.protocols.pbcast.FLUSH - Member-D: received RESUME, sending STOP_FLUSH to all
> But, since B is not a member of D's view, B does not receive this message.  
> (5) Now all future merge attempts fail, because B is stuck in a flush:
> 2012-02-18 22:15:31.186 [OOB-1,Clumpy Test Cluster,Member-B] WARN  org.jgroups.protocols.pbcast.GMS - Member-B: GMS flush by coordinator failed
> 2012-02-18 22:15:54.380 [OOB-2,Clumpy Test Cluster,Member-B] WARN  org.jgroups.protocols.pbcast.GMS - Member-B: GMS flush by coordinator failed
> 2012-02-18 22:16:13.705 [OOB-1,Clumpy Test Cluster,Member-B] WARN  org.jgroups.protocols.pbcast.GMS - Member-B: GMS flush by coordinator failed
> Note that I have implemented a workaround in my application where I:
> -  start a long-ish timer in the block() callback; and stop that timer in unblock()
> -  if the timer is allowed to pop, call channel.stopFlush()
> This seems to be allowing the group to recover.  Any comments on whether this is a good or bad idea would be appreciated.

--
This message is automatically generated by JIRA.
If you think it was sent incorrectly, please contact your JIRA administrators: https://issues.jboss.org/secure/ContactAdministrators!default.jspa
For more information on JIRA, see: http://www.atlassian.com/software/jira