[jboss-jira] [JBoss JIRA] (JGRP-1387) MERGE3: merging in large clusters

[Bela Ban (Created) (JIRA)]

MERGE3: merging in large clusters
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                 Key: JGRP-1387
                 URL: https://issues.jboss.org/browse/JGRP-1387
             Project: JGroups
          Issue Type: Feature Request
            Reporter: Bela Ban
            Assignee: Bela Ban
             Fix For: 3.1


MERGE2 has the issue that concurrent merges are frequent with large clusters. MERGE3 will change this and works as follows:
- Every node sends a multicast with its address, logical name, physical address and ViewId every N seconds
- Every node collects this information and - every N * 1.5 seconds - determines (a) whether we have different ViewIds and (if so) (b) determines the merge leader from the collected info
- The merge leader then collects the different Views from the merge participants, and sends a MERGE event up the stack, so that GMS can start the merge

The benefits of MERGE3 are:
- Good for large clusters, geared toward UDP based stacks
- Only 1 merge in the cluster at any time
- The collection of information to see whether a merge is needed is spaced out over a longer time period (N secs), compared to MERGE2, which uses Discovery.findAllViews(), which consists of a multicast and N unicasts. This might cause temporary congestion and packet loss
- On a merge, the members already have the logical-physical address mapping (unlike MERGE2) 

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