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https://issues.apache.org/jira/browse/HBASE-71?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12573866#action_12573866
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Bryan Duxbury commented on HBASE-71:
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How does a region server know when it's overloaded compared to other servers?
In DFS we have the convenient metric of the fixed amount of disk space to tell
us when heterogeneous servers are overloaded. We could do something like memory
usage, but that's not necessarily fixed, nor is it clear that high memory usage
actually indicates high load in all circumstances (other processes may be using
a lot of memory, causing swapping, vs HBase being the only program, so high
memory means nothing).
I certainly think that we should be able to manage heterogeneity at some point
in the future, but I think we should put off solving that issue for a while.
I will go ahead with the plan of region server reporting N regions each time,
and if the master determines the region server's load to be over the average,
it will unassign some of those. Like Stack says, if the region server is still
overloaded on the next report in, then it'll get some more regions shifted
around.
> [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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