[ 
https://issues.apache.org/jira/browse/HBASE-20186?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
 ]

Xiang Li updated HBASE-20186:
-----------------------------
    Description: 
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 
we could record which servers have been processed,  we could skip those.

  was:
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).


> 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
>         Environment: 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 that we do not need to scan each server again and 
> again, instead, we could record which servers have been processed and skip 
> them
>            Reporter: Xiang Li
>            Assignee: Xiang Li
>            Priority: Minor
>
> 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 we could record which servers have been processed,  we could skip those.



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