Vinay created HDFS-5112:
---------------------------

             Summary: NetWorkTopology#countNumOfAvailableNodes() is returning 
wrong value if excluded nodes passed are not part of the cluster tree
                 Key: HDFS-5112
                 URL: https://issues.apache.org/jira/browse/HDFS-5112
             Project: Hadoop HDFS
          Issue Type: Bug
          Components: namenode
    Affects Versions: 2.0.5-alpha, 3.0.0
            Reporter: Vinay
            Assignee: Vinay


I got "File /hdfs_COPYING_ could only be replicated to 0 nodes instead of 
minReplication (=1).  There are 1 datanode(s) running and 1 node(s) are 
excluded in this operation." in the following case

1. 2 DNs cluster,
2. One of the datanodes was not responding from last 10 min, but about to 
detect as dead at NN.
3. Tried to write one file, for the block NN allocated both DNs.
4. Client While creating the pipeline took some time to detect one node failure.
5. Before client detects pipeline failure, NN side dead node was removed from 
cluster map.
6. Now, client has abandoned previous block and asked for new block with dead 
node in excluded list and got above exception even though one more node was 
available live.

When I dig this more, found that,
{{NetWorkTopology#countNumOfAvailableNodes()}} is not giving correct count when 
the excludeNodes passed from client are not part of the cluster map.


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