Add zk.updateServerList(newServerList)
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Key: ZOOKEEPER-1355
URL: https://issues.apache.org/jira/browse/ZOOKEEPER-1355
Project: ZooKeeper
Issue Type: New Feature
Components: java client
Reporter: Alexander Shraer
Assignee: Alexander Shraer
Fix For: 3.5.0
When the set of servers changes, we would like to update the server list stored
by clients without restarting the clients.
Moreover, assuming that the number of clients per server is the same (in
expectation) in the old configuration (as guaranteed by the current list
shuffling for example), we would like to re-balance client connections across
the new set of servers in a way that a) the number of clients per server is the
same for all servers (in expectation) and b) there is no excessive/unnecessary
client migration.
It is simple to achieve (a) without (b) - just re-shuffle the new list of
servers at every client. But this would create unnecessary migration, which
we'd like to avoid.
We propose a simple probabilistic migration scheme that achieves (a) and (b) -
each client locally decides whether and where to migrate when the list of
servers changes. The attached document describes the scheme and shows an
evaluation of it in Zookeeper. We also implemented re-balancing through a
consistent-hashing scheme and show a comparison. We derived the probabilistic
migration rules from a simple formula that we can also provide, if someone's
interested in the proof.
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