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https://issues.apache.org/jira/browse/ZOOKEEPER-29?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12699407#action_12699407
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Flavio Paiva Junqueira commented on ZOOKEEPER-29:
-------------------------------------------------
Just to motivate a little more this scheme, taking the example above, suppose
that each group corresponds to the set of ZooKeeper servers in a colocation. To
form a quorum, we just need to get a majority of servers from a majority of
groups. This gives us quorums of size 4, whereas majority quorums would require
5. This model is reasonable, though, as it is reasonable to expect that at
least a majority of colocations have a majority of servers up and running.
This idea actually appeared in the following citation (apologies for the
self-reference): http://dslab.epfl.ch/hotdep/2005/papers/junqueira_dependent.pdf
Another question that may arise is how leader election changes. With this
scheme it only changes minimally. In the current trunk code, we always wait for
a majority of votes, and that's because we have majority quorums hardcoded.
With this patch, we check if we have a quorum, and a quorum can be a majority,
as we have currently, or a different quorum system as the one of the example.
> Flexible quorums
> ----------------
>
> Key: ZOOKEEPER-29
> URL: https://issues.apache.org/jira/browse/ZOOKEEPER-29
> Project: Zookeeper
> Issue Type: New Feature
> Components: server
> Reporter: Patrick Hunt
> Assignee: Flavio Paiva Junqueira
> Fix For: 3.2.0
>
> Attachments: ZOOKEEPER-29.patch, ZOOKEEPER-29.patch,
> ZOOKEEPER-29.patch, ZOOKEEPER-29.patch, ZOOKEEPER-29.patch, ZOOKEEPER-29.patch
>
>
> Moved from SourceForge to Apache.
> http://sourceforge.net/tracker/index.php?func=detail&aid=1938782&group_id=209147&atid=1008547
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