[GitHub] [hadoop] iwasakims commented on pull request #4107: HDFS-16521. DFS API to retrieve slow datanodes

[GitBox <gi...@apache.org>]

iwasakims commented on pull request #4107:
URL: https://github.com/apache/hadoop/pull/4107#issuecomment-1082994545


   I agree with @ayushtkn that modifying ClientProtocol is overkill for the use case. @virajjasani
   
   > While I agree that JMX metric for slownode is already available, not every downstreamer might have access to it directly, for instance in K8S managed clusters, unless port forward is enabled (not so common case in prod), HDFS downstreamer would not be able to access JMX metrics.
   
   Thanks to [JMXJsonServlet](https://github.com/apache/hadoop/blob/trunk/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/jmx/JMXJsonServlet.java), we can get metrics in JSON format via HTTP/HTTPS port of NameNode without additional configuration. JSON on HTTP is usually easier to access from outside/downstream than Protobuf on RPC.
   
   ```
   $ curl namenode:9870/jmx?qry=Hadoop:service=NameNode,name=NameNodeStatus
   {
     "beans" : [ {
       "name" : "Hadoop:service=NameNode,name=NameNodeStatus",
       "modelerType" : "org.apache.hadoop.hdfs.server.namenode.NameNode",
       "NNRole" : "NameNode",
       "HostAndPort" : "localhost:8020",
       "SecurityEnabled" : false,
       "LastHATransitionTime" : 0,
       "BytesWithFutureGenerationStamps" : 0,
       "SlowPeersReport" : "[]",
       "SlowDisksReport" : null,
       "State" : "active"
     } ]
   }
   ```
   
   How about enhancing metrics if the current information in the SlowPeersReport is insufficient?
   


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