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From "Andrew Purtell (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HBASE-1110) Distribute the master role to HRS after ZK integration
Date Tue, 30 Mar 2010 08:16:27 GMT

    [ https://issues.apache.org/jira/browse/HBASE-1110?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12851306#action_12851306
] 

Andrew Purtell commented on HBASE-1110:
---------------------------------------

ZK 3.3.0 claims to have a worked distributed queue recipe implementation. 

Use it for region assignment? (Master could release region after log split or table create
and one regionservers can coordinate picking them up via the distributed queue.) 

Use it for log splitting? Master can put up logs to split into the queue and regionservers
can take it on as their load and health allow?

> Distribute the master role to HRS after ZK integration
> ------------------------------------------------------
>
>                 Key: HBASE-1110
>                 URL: https://issues.apache.org/jira/browse/HBASE-1110
>             Project: Hadoop HBase
>          Issue Type: Improvement
>            Reporter: Andrew Purtell
>            Priority: Critical
>             Fix For: 0.21.0
>
>
> 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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