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From "stack (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HBASE-71) [hbase] Master should rebalance region assignments periodically
Date Fri, 29 Feb 2008 04:38:51 GMT

    [ https://issues.apache.org/jira/browse/HBASE-71?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12573589#action_12573589
] 

stack commented on HBASE-71:
----------------------------

I like the idea of only rebalancing when an 'event' that would require rebalancing.  I like
your list too except I wouldn't include splits.  Its just adding a single region to the mix
and I'd imagine rebalance a heavy-weight process that we shouldn't trigger if only one new
region in the mix?  Maybe after the Nth split force a balance review?

Rather than RegionManager telling the region its overloaded, isn't the regionserver better
able to determine whether its overloaded or not? (Would allow for cluster of heterogeneous
servers).  I suppose there should be a means of the regionserver saying "I'm full" before
it gets to overloaded state so that master doesn't put it over the edge.

On the region assignment operation, currently a split or assignment runs as a message delivered
as part of the normal batch-messaging-on-a-period mechanism.  I was thinking that when it
comes to assigning regions, we should short-circuit and deliver the split notice or assignment
to happen w/o delay.  Currently we have subsecond splits but can take a long time before the
daughters are up and running in their new locations.

On master not knowing which region to reassign, yeah, regionserver should suggest N (Why not
one to keep it simple?  Can deliver an other overloaded notice if needs to shed more)... presuming
its regionserver that is saying "I'm overloaded".

> [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
>            Assignee: 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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