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https://issues.apache.org/jira/browse/ZOOKEEPER-107?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12730384#action_12730384
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Raghu S commented on ZOOKEEPER-107:
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Sorry to jump around bit, I thought I will mention this if we haven't already
talked about it. How do we plan to deal with a situation when a set of nodes
can form a majority but can't form an ensemble because one or more peers have
a grossly outdated configuration? Say an ensemble of ABCDE moved to EFGHI while
E was offline and only EFG are up? They form a majority but can't form an
ensemble since E doesn't know about any of the other servers yet?
One way to address this is to implement an out of band synchronization
mechanism in which E will realize that the ensemble has changed when F and G
try to connect to E and have one them synchronize E's logs since their last
know zxids are ahead of E's. E can then attempt to restart an election. Also,
it is possible that F and G could see different ensembles (F is a bit out
dated, G is the most up to date), in which case E might first sync up form F
and then both E and F sync up form G if G comes online a bit later.
Any simpler solutions?
> Allow dynamic changes to server cluster membership
> --------------------------------------------------
>
> Key: ZOOKEEPER-107
> URL: https://issues.apache.org/jira/browse/ZOOKEEPER-107
> Project: Zookeeper
> Issue Type: Improvement
> Components: server
> Reporter: Patrick Hunt
> Assignee: Henry Robinson
> Attachments: SimpleAddition.rtf
>
>
> Currently cluster membership is statically defined, adding/removing hosts
> to/from the server cluster dynamically needs to be supported.
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