[jira] (HBASE-17565) StochasticLoadBalancer may incorrectly skip balancing due to skewed multiplier sum

["stack (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HBASE-17565?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15847258#comment-15847258 ] 

stack commented on HBASE-17565:
-------------------------------

[~tedyu] Quit this forking of development/attention and duplication of effort. HBase development is a collaborative affair. It is not a competition. If you have problem or contrib to the patch up on HBASE-17261, please add comment there. Your actions here only baffle the contributor as they ask themselves what was wrong w/ their patch and why their effort cast aside. HBASE-17261 has precedent, has a tie to the issue that introduced the bug, and it has a patch that seems to address the issue. All that was missing was exercise of the contributors posted patch. The decent thing would be resolve of this item as a duplicate and help landing a fix, preferably by a new contributor.

> 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
>
>
> 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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