[jira] [Created] (HBASE-25882) TableSkewCostFunction may cost unnecessary calculation steps when balancing by table

["Xiaolin Ha (Jira)" <ji...@apache.org>]

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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