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https://issues.apache.org/jira/browse/HBASE-25739?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17318128#comment-17318128
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David Manning commented on HBASE-25739:
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Can you update the description since we are no longer using standard deviation
in the current proposal?
Do you have any thoughts on the current default weight of
TableSkewCostFunction? DEFAULT_TABLE_SKEW_COST = 35 - I wonder if this still
makes sense given this change, or if it had this value due to the previous cost
calculation. I don't really know myself... intuitively it makes sense to me to
leave at 35, as it seems more important than most other cost functions, and
less important than RegionCountSkewCostFunction. I was just curious if you had
any thoughts.
Thanks for the nice improvement.
> 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
> Priority: Major
>
> 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 the standard deviation of the count
> per region server to detect this scenario, generating a cost of 3.1/31 = 0.1
> in this case.
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