support balancing of client load across servers in an ensemble
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Key: ZOOKEEPER-571
URL: https://issues.apache.org/jira/browse/ZOOKEEPER-571
Project: Zookeeper
Issue Type: Improvement
Components: quorum, server
Reporter: Patrick Hunt
Currently the ensemble does not ensure a balanced load across servers in an
ensemble. Clients randomly connect to
a server, which typically balances the number of sessions. However there are
problems with this:
1) session count is balanced, but not session load
2) if server A goes down all of the sessions on that server migrate to other
servers in the cluster randomly, this is fine, however
when server A comes back into service it will have no sessions, and migration
of sessions from other servers may take time
The quorum should probably have some way of broadcasting load, and occasionally
re-balance the sessions based on
this information. Might be tricky though, want to ensure that we aren't
constantly ping-ponging sessions to servers.
Probably need some hysteresis as well as limit the frequency. Real time tuning
would need to be supported.
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