[ http://jira.jboss.com/jira/browse/JGRP-31?page=history ]
Bela Ban resolved JGRP-31:
--------------------------
Resolution: Done
I added the merge_leader flag to GMS. Another possibility to solve this is to
use the TCP:MPING combination
> Problem with MERGE2 when not using multicast
> --------------------------------------------
>
> Key: JGRP-31
> URL: http://jira.jboss.com/jira/browse/JGRP-31
> Project: JGroups
> Type: Bug
> Versions: 2.2.8
> Environment: SUN Java 1.4.2_05
> Reporter: B.S.Navin
> Assignee: Bela Ban
> Fix For: 2.2.8
>
>
> Hi,
> There is one case in which MERGE2 will fail while using TCPPING/UDP(without
> mcast):
> ========================================
> The initial_hosts property is "abc.com[7800];xyz.com[7801]".
> These 2 machines are permanent group members (if they are up, they will be
> members of the group).
> Now there are numerous other programs on different machines that may
> dynamically join and leave the group. These members are not known before hand
> and cannot be specified in the initial_hosts property.
> The members on abc.com and xyz.com are started and they join the same group.
> Now another member from "mnop.com" starts and joins the group. The
> co-ordinator will be abc.com
> A network problem occurs and mnop.com is separated from abc.com and xyz.com
> mnop.com forms its own single-member group with itself as the co-ordinator.
> Now suppose the network problem is fixed. The MERGE2 protocol on mnop.com
> periodically checks on the initial_hosts list to see if they are up. It now
> finds that abc.com is reachable and decides that abc.com is the leader (by
> lexical sorting) and will take care of the merging. So it does not go ahead
> with the merge.
> On the other hand, the MERGE2 protocol on both abc.com and xyz.com just check
> if they can find members on the initial_hosts with a different co-ordinator.
> Both of them never consider mnop.com as it is not in the initial_hosts list
> So mnop.com will never be merged with the group.
> ========================================
> Even the new MERGE3 & MERGEFAST protocols don't seem to help here. I checked
> them out and found the following:
> MERGEFAST works only if multicast is used, which is not my case.
> MERGE3 just sends "I am co-ordinator" messages to a null destination. So in
> the case where multicast is enabled, it goes to all possible members. But in
> my case, with multicast disabled, the message will only be unicast to each
> member of the current group. So in the above example, the "I am co-ordinator"
> messages will never go to mnop.com after the network problem.
> So even MERGE3 does not work in this case.
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