[jira] Commented: (HBASE-71) [hbase] Master should rebalance region assignments periodically

["Bryan Duxbury (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HBASE-71?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12568370#action_12568370 ] 

Bryan Duxbury commented on HBASE-71:
------------------------------------

Speaking with a colleague, instead of rebalancing periodically, maybe we should just enqueue a rebalancing to occur whenever any event occurs that could introduce an imbalance.  I'm thinking:

 * Whole cluster comes online
 * Region server comes online
 * Region server goes offline
 * Region splits
 * Region merges (for the future...)
 
This would allow us to only selectively reassign regions. Are there any other events that should be tracked that would require us to rebalance?


> [hbase] Master should rebalance region assignments periodically
> ---------------------------------------------------------------
>
>                 Key: HBASE-71
>                 URL: https://issues.apache.org/jira/browse/HBASE-71
>             Project: Hadoop HBase
>          Issue Type: Improvement
>          Components: master
>            Reporter: Bryan Duxbury
>             Fix For: 0.2.0
>
>
> The master currently only does region assignments at startup or when there are splits or dead regionservers. This means that if you join a new regionserver to the cluster after startup, it does not get assigned a fair share of the already-served regions as you would expect. It only gets a share of new regions being served.
> The master should periodically check the balance of regions, based on whatever assignment function, instead of in reaction to the above listed events.

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