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https://issues.apache.org/jira/browse/HDDS-2199?focusedWorklogId=321990&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-321990
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ASF GitHub Bot logged work on HDDS-2199:
----------------------------------------

                Author: ASF GitHub Bot
            Created on: 02/Oct/19 15:35
            Start Date: 02/Oct/19 15:35
    Worklog Time Spent: 10m 
      Work Description: elek commented on pull request #1551: HDDS-2199 In 
SCMNodeManager dnsToUuidMap cannot track multiple DNs on the same host
URL: https://github.com/apache/hadoop/pull/1551#discussion_r330622132
 
 

 ##########
 File path: 
hadoop-hdds/server-scm/src/main/java/org/apache/hadoop/hdds/scm/server/SCMBlockProtocolServer.java
 ##########
 @@ -295,7 +297,33 @@ public ScmInfo getScmInfo() throws IOException {
     boolean auditSuccess = true;
     try{
       NodeManager nodeManager = scm.getScmNodeManager();
-      Node client = nodeManager.getNodeByAddress(clientMachine);
 
 Review comment:
   > Eg this is passed in:
   > 
   > DN0, DN5, DN10, DN15
   > 
   > On the client machine is:
   > 
   > DN1, DN6, DN10 and DN16
   
   Not sure If I understand well. I think there are two parameters
   
     1. The host name of the client (eg. DN10)
     2. List of datanode UUIDs  (DN1, DN6, DN10)
   
   The task is to sort the list of datanode UUIDs, with prioritizing the client 
machine.
   
   First the client hostname is converted to UUID. This is the part which is 
replaced by this complex block. If it could not been converted it can be null. 
After that the topology logic sorts the list. `sortByDistanceCost`.
   
   IMHO this functionality can be implemented my 4 lines of code, but fix me If 
I am wrong.
 
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Issue Time Tracking
-------------------

    Worklog Id:     (was: 321990)
    Time Spent: 3.5h  (was: 3h 20m)

> In SCMNodeManager dnsToUuidMap cannot track multiple DNs on the same host
> -------------------------------------------------------------------------
>
>                 Key: HDDS-2199
>                 URL: https://issues.apache.org/jira/browse/HDDS-2199
>             Project: Hadoop Distributed Data Store
>          Issue Type: Bug
>    Affects Versions: 0.5.0
>            Reporter: Stephen O'Donnell
>            Assignee: Stephen O'Donnell
>            Priority: Major
>              Labels: pull-request-available
>          Time Spent: 3.5h
>  Remaining Estimate: 0h
>
> Often in test clusters and tests, we start multiple datanodes on the same 
> host.
> In SCMNodeManager.register() there is a map of hostname -> datanode UUID 
> called dnsToUuidMap.
> If several DNs register from the same host, the entry in the map will be 
> overwritten and the last DN to register will 'win'.
> This means that the method getNodeByAddress() does not return the correct 
> DatanodeDetails object when many hosts are registered from the same address.
> This method is only used in SCMBlockProtocolServer.sortDatanodes() to allow 
> it to see if one of the nodes matches the client, but it need to be used by 
> the Decommission code.
> Perhaps we could change the getNodeByAddress() method to returns a list of 
> DNs? In normal production clusters, there should only be one returned, but in 
> test clusters, there may be many. Any code looking for a specific DN entry 
> would need to iterate the list and match on the port number too, as host:port 
> would be the unique definition of a datanode.



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