Clara Xiong created HBASE-25739: ----------------------------------- Summary: 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
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 the standard deviation of the count per region server to detect this scenario, generating a cost of 3.1/31 = 0.1 in this case. -- This message was sent by Atlassian Jira (v8.3.4#803005)