Xiaolin Ha created HBASE-25882:
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Summary: TableSkewCostFunction may cost unnecessary calculation
steps when balancing by table
Key: HBASE-25882
URL: https://issues.apache.org/jira/browse/HBASE-25882
Project: HBase
Issue Type: Improvement
Components: Balancer
Affects Versions: 2.0.0, 3.0.0-alpha-1
Reporter: Xiaolin Ha
Assignee: Xiaolin Ha
When using balance by table, the StochasticLoadBalancer will create the cluster
state according to the regions distribution of only one table. As a result,
the TableSkewCostFunction should be replaced by the RegionCountSkewCostFunction
when the table count of the cluster state is less than 2.
The most important problem is that, TableSkewCostFunction will cause
unnecessary calculation steps when there is only one table. The cost it
computed may be incorrect.
For example, there are 5 online regionservers, and there is only one table with
exactly one region, the cluster state is [0,0,0,0,1]. Then the cost of
TableSkewCostFunction will be 1 (expect value is 0), because max=1, min=0.25,
value=1. And the computedMaxSteps will be larger than 0, some balance actions
will be generated to decrease the cost. But all the actions is meaningless for
the skew count.
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