Kihwal Lee created HDFS-11015:

             Summary: Enforce timeout in balancer
                 Key: HDFS-11015
             Project: Hadoop HDFS
          Issue Type: Bug
            Reporter: Kihwal Lee

1) Hung node detection: HDFS-6247 has removed the socket read timeout while 
adding the periodic response for slow block moves. However, the removal of the 
long timeout wasn't necessary.  The timeout is still useful for avoiding hung 
nodes and does not interfere with slow moves.

2) Enforcing the iteration limit:The 20 minute iteration limit is supposed to 
be enforced, but it is not. An iteration can easily stretch to 30 to 40 minutes 
with a long tail. Because of the long tails, the balancer throughput does not 
reach its full potential.

3) Slow move detection: For improved throughput, imposing block move timeout is 
sometimes necessary.  We have seen an iteration taking over 2 hours because of 
one slow block move.  This is mainly for catching exceptionally slow moves.  
Even if the balancer stops waiting, the move will continue and finish.

In order to not undo what  HDFS-6247 tried to achieve, it should be possible to 
configure off 3).

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