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From "Zhe Zhang (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HDFS-10966) Enhance Dispatcher logic on deciding when to give up a source DataNode
Date Wed, 05 Oct 2016 22:41:20 GMT
Zhe Zhang created HDFS-10966:
--------------------------------

             Summary: Enhance Dispatcher logic on deciding when to give up a source DataNode
                 Key: HDFS-10966
                 URL: https://issues.apache.org/jira/browse/HDFS-10966
             Project: Hadoop HDFS
          Issue Type: Bug
          Components: balancer & mover
            Reporter: Zhe Zhang
            Assignee: Mark Wagner


When a {{Dispatcher}} thread works on a source DataNode, in each iteration it tries to execute
a {{PendingMove}}. If no block is moved after 5 iterations, this source (over-utlized) DataNode
is given up for this Balancer iteration (20 mins). This is problematic if the source DataNode
was heavily loaded in the beginning of the iteration. It will quickly encounter 5 unsuccessful
moves and be abandoned.

We should enhance this logic by e.g. using elapsed time instead of number of iterations.
{code}
// Check if the previous move was successful
        } else {
          // source node cannot find a pending block to move, iteration +1
          noPendingMoveIteration++;
          // in case no blocks can be moved for source node's task,
          // jump out of while-loop after 5 iterations.
          if (noPendingMoveIteration >= MAX_NO_PENDING_MOVE_ITERATIONS) {
            LOG.info("Failed to find a pending move "  + noPendingMoveIteration
                + " times.  Skipping " + this);
            resetScheduledSize();
          }
        }
{code}



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