[jboss-jira] [JBoss JIRA] (JGRP-2276) MERGE3: a dead member as merge leader will never trigger a merge

[Bela Ban (JIRA)]

     [ https://issues.jboss.org/browse/JGRP-2276?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Bela Ban updated JGRP-2276:
---------------------------
    Description: 
When we have member(s) which have a view with a dead member as coordinator, when the dead member becomes part of the subgroup coordinators and _happens to be chosen as merge leader_, then a merge will never ensue. 

Example:
* Member 2 (with view 2|5) was the previous coordinator and left the cluster, installing view 3|6 before stopping
** View 2|5=\{2,3,4,5,6,7\}; view 3|6=\{3,4,5,6,7\}
* Member 7 didn't get view 3|6 and still has view 2|5
* Everybody else has view 3|6
* MERGE3 gets the following views:
** 2|5: 7 // member 7 has this view
** 3|6: 3,4,5,6 // members 3,4,5 and 6 have this view
* 2 and 3 are added to a _sorted set_ and the first member of the set (2) is chose as merge leader. 3 doesn't take any action, as it notices it won't be the merge leader
** The reason 2 was first in the sorted set is that (possibly by coincidence) its UUID is *lower* than that of 3. If this wasn't the case, 3 would be merge leader and start (and successfully complete) a merge. However, with dead member 2 being picked as merge leader, a merge will never be triggered!


  was:
When we have member(s) which have a view with a dead member as coordinator, when the dead member becomes part of the subgroup coordinators and _happens to be chosen as merge leader_, then a merge will never ensue. 

Example:
* Member 2 (with view 2|5) was the previous coordinator and left the cluster, installing view 3|6 before stopping
** View 2|5=\{2,3,4,5,6,7\}; view 3|6=\{3,4,5,6,7\}
* Member 7 didn't get view 3|6 and still has view 2|5
* Everybody else has view 3|6
* MERGE3 gets the following views:
** 2|5: 7 // member 7 has this view
** 3|6: 3,4,5,6 // members 3,4,5 and 6 have this view
* 2 and 3 are added to a _sorted set_ and the first member of the set (2) is chose as merge leader. 3 doesn't take any action, as it notices it won't be the merge leader
** The reason 2 was first in the sorted set is that (possibly by coincidence) its UUID is *lower* than that of 3. If this wan't the case, 3 would be merge leader and start (and successfully complete) a merge. However, with dead member 2 being picked as merge leader, a merge will never be triggered!




> MERGE3: a dead member as merge leader will never trigger a merge
> ----------------------------------------------------------------
>
>                 Key: JGRP-2276
>                 URL: https://issues.jboss.org/browse/JGRP-2276
>             Project: JGroups
>          Issue Type: Bug
>            Reporter: Bela Ban
>            Assignee: Bela Ban
>             Fix For: 4.0.12
>
>
> When we have member(s) which have a view with a dead member as coordinator, when the dead member becomes part of the subgroup coordinators and _happens to be chosen as merge leader_, then a merge will never ensue. 
> Example:
> * Member 2 (with view 2|5) was the previous coordinator and left the cluster, installing view 3|6 before stopping
> ** View 2|5=\{2,3,4,5,6,7\}; view 3|6=\{3,4,5,6,7\}
> * Member 7 didn't get view 3|6 and still has view 2|5
> * Everybody else has view 3|6
> * MERGE3 gets the following views:
> ** 2|5: 7 // member 7 has this view
> ** 3|6: 3,4,5,6 // members 3,4,5 and 6 have this view
> * 2 and 3 are added to a _sorted set_ and the first member of the set (2) is chose as merge leader. 3 doesn't take any action, as it notices it won't be the merge leader
> ** The reason 2 was first in the sorted set is that (possibly by coincidence) its UUID is *lower* than that of 3. If this wasn't the case, 3 would be merge leader and start (and successfully complete) a merge. However, with dead member 2 being picked as merge leader, a merge will never be triggered!



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