Kahlil Oppenheimer created HBASE-17706:
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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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