Distribute the master role to HRS after ZK integration
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Key: HBASE-1110
URL: https://issues.apache.org/jira/browse/HBASE-1110
Project: Hadoop HBase
Issue Type: Improvement
Reporter: Andrew Purtell
Priority: Minor
After ZK integration, the master role can be distributed out to the HRS as
group behaviors mediated by synchronization and rendezvous points in ZK.
- State sharing, for example load.
-- Load information can be shared with neighbors via ephemeral child status
znodes of a znode representing the cluster root.
-- Region servers can periodically walk the status nodes of their neighbors.
If they find themselves loaded relative to others, they can release regions. If
they find themselves less loaded relative to others, they can be more
aggressive about finding unassigned regions (see below).
- Ephemeral znodes for region ownership, e.g. /hbase//<region>/<ephemeral-node>
-- Use a permanent child of <region> to serve as a 'dirty' flag, removed
during normal close.
- A distributed queue for region assignment.
-- When coming up, HRS can check the assignment queue for candidates.
-- HRS shutdown includes marking regions clean and moving them onto
assignment queue.
-- All/any HRS can do occasional random walks over region leases looking for
expired-dirty state (when timeout causes ZK to delete the ephemeral node
representing the lease), and can helpfully move them first to a queue (+
barrier) for splitting then onto the assignment queue.
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