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From "Kahlil Oppenheimer (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HBASE-17706) TableSkewCostFunction improperly computes max skew
Date Tue, 28 Feb 2017 04:40:45 GMT
Kahlil Oppenheimer created HBASE-17706:

             Summary: TableSkewCostFunction improperly computes max skew
                 Key: HBASE-17706
                 URL: https://issues.apache.org/jira/browse/HBASE-17706
             Project: HBase
          Issue Type: Bug
          Components: Balancer
    Affects Versions: 1.2.0
         Environment: CentOS Derivative with a derivative of the 3.18.43 kernel. HBase on
CDH5.9.0 with some patches. HDFS CDH 5.9.0 with no patches.
            Reporter: Kahlil Oppenheimer
            Priority: Minor

We noticed while running unit tests that the TableSkewCostFunction computed cost did not change
as the balancer ran and simulated moves across the cluster. After investigating, we found
that this happened in particular when the cluster started out with at least one table very
strongly skewed.

We noticed that the TableSkewCostFunction depends on a field of the BaseLoadBalancer.Cluster
class called numMaxRegionsPerTable, but this field is not properly maintained as regionMoves
are simulated for the cluster. The field only ever increases as the maximum number of regions
per table increases, but it does not decrease as the maximum number per table goes down.

This patch corrects that behavior so that the field is accurately maintained, and thus the
TableSkewCostFunction produces a more correct value as the balancer runs.

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