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Subject [GitHub] [hadoop] sodonnel commented on a change in pull request #1551: HDDS-2199 In SCMNodeManager dnsToUuidMap cannot track multiple DNs on the same host
Date Thu, 03 Oct 2019 17:35:40 GMT
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_r331163439
 
 

 ##########
 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:
   Reflecting on this issue some more, I think the simplified logic you have suggested is
better and the problem is better solved in getDistanceByCost - rather than comparing just
the node objects are the same, we should test if they are the same hostname and if so treat
that as a zero distance match too.
   
   Unfortunately, as that method takes Node objects rather than DatanodeDetails, this is not
trivial to do.
   
   The code path under question here is only relevant for clusters with more than one datanode
on the same host, and by definition that is a non-production setup. The only consequence of
the change you have suggested over my original code, is that the client may get the wrong
'cost to reach a datanode' sometimes on test clusters - nothing will fail, so the impact of
this issue is very low.
   
   Therefore if you are happy, I think we should commit the latest version (which has your
simplified logic) and create a followup Jira to look into fixing getDistanceByCost somehow.

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