[GitHub] [hadoop] sodonnel commented on a change in pull request #1551: HDDS-2199 In SCMNodeManager dnsToUuidMap cannot track multiple DNs on the same host

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sodonnel commented on a change in 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_r330481300
 
 

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 File path: hadoop-hdds/server-scm/src/main/java/org/apache/hadoop/hdds/scm/server/SCMBlockProtocolServer.java
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 @@ -295,7 +297,33 @@ public ScmInfo getScmInfo() throws IOException {
     boolean auditSuccess = true;
     try{
       NodeManager nodeManager = scm.getScmNodeManager();
-      Node client = nodeManager.getNodeByAddress(clientMachine);
 
 Review comment:
   I am not certain how this sortDatanodes() call is used. Is it on the read path or write path? I was assuming it was on the read path, but write path may be different if all the cluster DNs are passed into the method - then you would always get a match.
   
   A list of DNs (UUIDs) are passed into the method, and then we retrieve a list of DatanodeDetails running on the client machine. The client machine can then be set to one of those DatanodeDetails, but it is not guaranteed that the first in the list will match on of the UUIDs passed into the method.
   
   Eg this is passed in:
   
   DN0, DN5, DN10, DN15
   
   On the client machine is:
   
   DN1, DN6, DN10 and DN16
   
   So only DN10 is a match with one that is passed it. If we just picked the first one (DN1) it would look like there is no DN on the client machine and then when the list and client machine are passed into sortByDistanceCost() at line 355, it would not give the expected result.
   
   The method receives a list of DNs, identified by UUID.

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