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From "Andrew Purtell (JIRA)" <j...@apache.org>
Subject [jira] Created: (HBASE-1110) Distribute the master role to HRS after ZK integration
Date Thu, 08 Jan 2009 06:04:46 GMT
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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