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From "stack (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HBASE-1110) Distribute the master role to HRS after ZK integration
Date Fri, 09 Jan 2009 00:04:59 GMT

    [ https://issues.apache.org/jira/browse/HBASE-1110?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12662183#action_12662183

stack commented on HBASE-1110:

Pertaining to master distribution -- not so much to zk integration (though it has a role to
play if a crash) -- log splitting is currently a hacked-up master responsibility that needs
to be distributed instead so splits are run promptly.  Also, our current split code does not
survive a master crash.  In ZK we can keep record of logs processed so on resumption, a distributed
splitting process can resume where it last left off.

> 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: 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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