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https://issues.apache.org/jira/browse/HBASE-22009?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16799217#comment-16799217
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Xu Cang commented on HBASE-22009:
---------------------------------

OK, I see what you are asking. I can do that. 

> Improve RSGroupInfoManagerImpl#getDefaultServers()
> --------------------------------------------------
>
>                 Key: HBASE-22009
>                 URL: https://issues.apache.org/jira/browse/HBASE-22009
>             Project: HBase
>          Issue Type: Improvement
>          Components: rsgroup
>            Reporter: Xiang Li
>            Assignee: Xiang Li
>            Priority: Minor
>             Fix For: 3.0.0, 2.2.0, 1.5.1, 2.2.1
>
>         Attachments: HBASE-22009.branch-1.000.patch, 
> HBASE-22009.master.000.addendum.patch, HBASE-22009.master.000.patch, 
> call_stack_getDefaultServers.png
>
>
> {code:title=RSGroupInfoManagerImpl.java|borderStyle=solid}
> private SortedSet<Address> getDefaultServers() throws IOException {
>   SortedSet<Address> defaultServers = Sets.newTreeSet();
>   for (ServerName serverName : getOnlineRS()) {
>     Address server = Address.fromParts(serverName.getHostname(), 
> serverName.getPort());
>     boolean found = false;
>     for (RSGroupInfo rsgi : listRSGroups()) {
>       if (!RSGroupInfo.DEFAULT_GROUP.equals(rsgi.getName()) && 
> rsgi.containsServer(server)) {
>         found = true;
>         break;
>       }
>     }
>     if (!found) {
>       defaultServers.add(server);
>     }
>   }
>   return defaultServers;
> }
> {code}
> That is a logic of 2 nested loops. And for each server, listRSGroups() 
> allocates a new LinkedList and calls Map#values(), both of which are very 
> heavy operations.
> Maybe the inner loop could be moved out, that is
> # Build a list of servers of other groups than default group
> # Iterate each online servers and check if it is in the list above. If it is 
> not, then it belongs to default group.



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