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https://issues.apache.org/jira/browse/HBASE-17565?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15856713#comment-15856713
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Ted Yu commented on HBASE-17565:
--------------------------------
In
https://builds.apache.org/job/HBase-TRUNK_matrix/2462/jdk=JDK%201.8%20(latest),label=Hadoop/testReport/org.apache.hadoop.hbase.master.balancer/TestStochasticLoadBalancer/testSmallCluster/
:
{code}
2017-02-07 19:49:15,444 INFO [main] balancer.StochasticLoadBalancer(296):
Skipping load balancing because balanced cluster; total cost is 0.0, sum
multiplier is 1062.0 min cost which need balance is 1.0
{code}
1.0 should only be used for testNeedBalance().
It turns out that testNeedBalance() should properly reset the value for min
cost.
> StochasticLoadBalancer may incorrectly skip balancing due to skewed
> multiplier sum
> ----------------------------------------------------------------------------------
>
> Key: HBASE-17565
> URL: https://issues.apache.org/jira/browse/HBASE-17565
> Project: HBase
> Issue Type: Bug
> Reporter: Ted Yu
> Assignee: Ted Yu
> Priority: Critical
> Fix For: 2.0.0, 1.4.0
>
> Attachments: 17565.v1.txt, 17565.v2.txt, 17565.v3.txt, 17565.v4.txt,
> 17565.v5.txt, 17565.v6.txt
>
>
> I was investigating why a 6 node cluster kept skipping balancing requests.
> Here were the region counts on the servers:
> 449, 448, 447, 449, 453, 0
> {code}
> 2017-01-26 22:04:47,145 INFO
> [RpcServer.deafult.FPBQ.Fifo.handler=1,queue=0,port=16000]
> balancer.StochasticLoadBalancer: Skipping load balancing because balanced
> cluster; total cost is 127.0171157050385, sum multiplier is 111087.0 min cost
> which need balance is 0.05
> {code}
> The big multiplier sum caught my eyes. Here was what additional debug logging
> showed:
> {code}
> 2017-01-27 23:25:31,749 DEBUG
> [RpcServer.deafult.FPBQ.Fifo.handler=9,queue=0,port=16000]
> balancer.StochasticLoadBalancer: class
> org.apache.hadoop.hbase.master.balancer.
> StochasticLoadBalancer$RegionReplicaHostCostFunction with multiplier 100000.0
> 2017-01-27 23:25:31,749 DEBUG
> [RpcServer.deafult.FPBQ.Fifo.handler=9,queue=0,port=16000]
> balancer.StochasticLoadBalancer: class
> org.apache.hadoop.hbase.master.balancer.
> StochasticLoadBalancer$RegionReplicaRackCostFunction with multiplier 10000.0
> {code}
> Note however, that no table in the cluster used read replica.
> I can think of two ways of fixing this situation:
> 1. If there is no read replica in the cluster, ignore the multipliers for the
> above two functions.
> 2. When cost() returned by the CostFunction is 0 (or very very close to 0.0),
> ignore the multiplier.
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