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
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.
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