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https://issues.apache.org/jira/browse/HBASE-25739?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Clara Xiong updated HBASE-25739:
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Description: 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. (was: 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 3.1/31 = 0.1 in this case.)
> 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 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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