[jira] Created: (HDFS-1431) Balancer should work with the logic of BlockPlacementPolicy

["Scott Chen (JIRA)" <ji...@apache.org>]

Balancer should work with the logic of BlockPlacementPolicy
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                 Key: HDFS-1431
                 URL: https://issues.apache.org/jira/browse/HDFS-1431
             Project: Hadoop HDFS
          Issue Type: Bug
          Components: balancer
    Affects Versions: 0.22.0
            Reporter: Scott Chen
            Assignee: Scott Chen
             Fix For: 0.22.0


Currently Balancer does not obtain information from BlockPlacementPolicy so it can transfer the blocks without checking with BlockPlacementPolicy.
This causes the policy break after the balancer balance the blocks.

There are some new BlockPlacementPolicy in HDFS-1094 and MAPREDUCE-1831 in which the block placement follows some pattern.
The pattern can be broken by Balancer.

I propose that we add the following method in BlockPlacementPolicy:
{code}
  abstract public boolean canBeMoved(String fileName, Block block,
    DatanodeInfo source, DatanodeInfo destination);
{code}

And make Balancer use it inside
{code}
  private boolean isGoodBlockCandidate(Source source,
      BalancerDatanode target, BalancerBlock block)
{code}

What do you think?

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