Daryn Sharp created HDFS-5946:
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             Summary: Webhdfs DN choosing code is flawed
                 Key: HDFS-5946
                 URL: https://issues.apache.org/jira/browse/HDFS-5946
             Project: Hadoop HDFS
          Issue Type: Bug
          Components: namenode, webhdfs
    Affects Versions: 3.0.0, 2.4.0
            Reporter: Daryn Sharp
            Priority: Critical


HDFS-5891 improved the performance of redirecting webhdfs clients to a DN.  
Instead of attempting a connection with a 1-minute timeout, the NN skips 
decommissioned nodes.

The logic appears flawed.  It finds the index of the first decommissioned node, 
if any, then:
* Throws an exception if index = 0, even if other nodes later in the list are 
not decommissioned.
* Else picks a random node prior to the index.  Let's say there are 10 
replicas, 2nd location is decommissioned.  All clients will be redirected to 
the first location even though there are 8 other valid locations.




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