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