[jira] [Created] (HDFS-8993) Balancer throws NPE

["He Xiaoqiao (JIRA)" <ji...@apache.org>]

He Xiaoqiao created HDFS-8993:
---------------------------------

             Summary: Balancer throws NPE
                 Key: HDFS-8993
                 URL: https://issues.apache.org/jira/browse/HDFS-8993
             Project: Hadoop HDFS
          Issue Type: Bug
          Components: balancer & mover
    Affects Versions: 2.4.1
            Reporter: He Xiaoqiao


Balancer may throw NPE because the following {{if Statements}}
{code:java|firstline=705}
          synchronized (block) {
            // update locations
            for (String datanodeUuid : blk.getDatanodeUuids()) {
              final BalancerDatanode d = datanodeMap.get(datanodeUuid);
              if (datanode != null) { // not an unknown datanode
                block.addLocation(d);
              }
            }
          }
{code}
Before moving block, Balancer divides into two step to get all DNs info & some blocks of DN from NN. Regarding one DN commission after {{getDatanodeReport}} then {{getBlockList}} and one block's target is above DN just right, It will throw NPE when dispatcher.



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