Xiang Li commented on HBASE-20186:

Thanks [~yuzhih...@gmail.com].
I corrected the format as well as some typos in comments. Please review it at 
your most convenience!

> Improve RSGroupBasedLoadBalancer#balanceCluster() to be more efficient when 
> calculating cluster state for each rsgroup
> ----------------------------------------------------------------------------------------------------------------------
>                 Key: HBASE-20186
>                 URL: https://issues.apache.org/jira/browse/HBASE-20186
>             Project: HBase
>          Issue Type: Improvement
>          Components: rsgroup
>            Reporter: Xiang Li
>            Assignee: Xiang Li
>            Priority: Minor
>         Attachments: HBASE-20186.master.000.patch, 
> HBASE-20186.master.001.patch
> In RSGroupBasedLoadBalancer
> {code}
> public List<RegionPlan> balanceCluster(Map<ServerName, List<RegionInfo>> 
> clusterState)
> {code}
> The second half of the function is to calculate region move plan for regions 
> which have been already placed according to the rsgroup assignment, and it is 
> calculated one rsgroup after another.
> The following logic to check if a server belongs to the rsgroup is not quite 
> efficient, as it does not make good use of the fact that servers in 
> RSGroupInfo is a TreeSet.
> {code}
> for (Address sName : info.getServers()) {
>   for(ServerName curr: clusterState.keySet()) {
>     if(curr.getAddress().equals(sName)) {
>       groupClusterState.put(curr, correctedState.get(curr));
>     }
>   }
> }
> {code}
> Given there are m region servers in the cluster and n region servers for each 
> rsgroup in average, the code above has time complexity as O(m * n), while 
> using TreeSet's contains(), the time complexity could be reduced to O (m * 
> logn).
> Another improvement is we do not need to scan every server for each rsgroup. 
> If the processed server could be recorded,  we could skip those.

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