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https://issues.apache.org/jira/browse/HBASE-25739?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17382627#comment-17382627
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Hudson commented on HBASE-25739:
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Results for branch branch-2.3
[build #256 on
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> TableSkewCostFunction need to use aggregated deviation
> ------------------------------------------------------
>
> Key: HBASE-25739
> URL: https://issues.apache.org/jira/browse/HBASE-25739
> Project: HBase
> Issue Type: Sub-task
> Components: Balancer, master
> Reporter: Clara Xiong
> Assignee: Clara Xiong
> Priority: Major
> Fix For: 2.5.0, 2.3.6, 3.0.0-alpha-2, 2.4.5
>
> Attachments:
> TEST-org.apache.hadoop.hbase.master.balancer.TestStochasticLoadBalancerBalanceCluster.xml,
>
> org.apache.hadoop.hbase.master.balancer.TestStochasticLoadBalancerBalanceCluster.txt
>
>
> TableSkewCostFunction uses the sum of the max deviation region per server for
> all tables as the measure of unevenness. It doesn't work in a very common
> scenario in operations. Say we have 100 regions on 50 nodes, two on each. We
> add 50 new nodes and they have 0 each. The max deviation from the mean is 1,
> compared to 99 in the worst case scenario of 100 regions on a single server.
> The normalized cost is 1/99 = 0.011 < default threshold of 0.05. Balancer
> wouldn't move. The proposal is to use aggregated deviation of the count per
> region server to detect this scenario, generating a cost of 100/198 = 0.5 in
> this case.
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