[jboss-jira] [JBoss JIRA] (JGRP-2277) GMS: change the way a coordinator leaves gracefully

[Bela Ban (JIRA)]

Bela Ban created JGRP-2277:
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             Summary: GMS: change the way a coordinator leaves gracefully
                 Key: JGRP-2277
                 URL: https://issues.jboss.org/browse/JGRP-2277
             Project: JGroups
          Issue Type: Enhancement
            Reporter: Bela Ban
            Assignee: Bela Ban
             Fix For: 4.0.13


Consider a cluster \{A,B,C,D\} with view A|5.

There's a discrepancy in handling coordinator A (1) leaving gracefully and (2) crashing.

When A crashes, the second-in-line (B) will install new view B|6=\{B,C,D\} in the cluster.

However, when A leaves _gracefully_, then *A itself* installs view B|6=\{B,C,D\}. The problem with this is that A is not able to retransmit the {{VIEW}} message to a member which dropped it, so inconsistencies may arise, which have to be healed by {{MERGE3}} (see JGRP-2276 for a description).

A better scheme would be for A to send a LEAVE message to the second-in-line (B), which then creates and installs view B|6, and then replies with a {{LEAVE_RSP}} message to A.

This has the following advantages:
* The code for handling a crashed coordinator, and a coordinator which leaves gracefully, is similar, and in both cases the second-in-line member installs the new view
* The second-in-line (B) stays up and can therefore retransmit a dropped {{VIEW}} message (contrary to A which terminates after a timeout). As long as A is able to send a {{LEAVE-REQ}} to B, B will handle it. If A crashes, B can also handle the view installation.



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