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https://issues.apache.org/jira/browse/HBASE-17969?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Allan Yang updated HBASE-17969:
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Attachment: (was: UTForMasterBranch.patch)
> Balance by table using SimpleLoadBalancer could end up imbalance
> ----------------------------------------------------------------
>
> Key: HBASE-17969
> URL: https://issues.apache.org/jira/browse/HBASE-17969
> Project: HBase
> Issue Type: Improvement
> Affects Versions: 1.1.10
> Reporter: Allan Yang
> Assignee: Allan Yang
> Attachments: HBASE-17969-branch-1.patch, HBASE-17969-branch-1.v2.patch
>
>
> This really happens in our production env.
> Here is a example:
> Say we have three RS named r1, r2, r3. A table named table1 with 3 regions
> distributes on these rs like this:
> r1 1
> r2 1
> r3 1
> Each rs have one region, it means table1 is balanced. So balancer will not
> run.
> If the region on r3 splits, then it becomes:
> r1 1
> r2 1
> r3 2
> For table1, in average, each rs will have min=1, max=2 regions. So still it
> is balanced, balancer will not run.
> Then a region on r3 splits again, the distribution becomes:
> r1 1
> r2 1
> r3 3
> In average, each rs will have min=1, max=2 regions. So balancer will run.
> For r1 and r2, they have already have min=1 regions. Balancer won't do any
> operation on them.
> But for r3, it exceed max=3, so balancer will remove one region from r3 and
> choose one rs from r1, r2 to move to.
> But r1 and r2 have the same load, so balancer will always choose r1 since
> servername r1 < r2(alphabet order, sorted by ServerAndLoad's compareTo
> method). It is OK for table1 itself. But if every table in the cluster have
> similar situations like table1, then the load in the cluster will always be
> like r1 > r2 > r3.
> So, the solution here is when each rs reach min regions (min=total region /
> servers), but there still some region need to move, shuffle the regionservers
> before move.
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