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https://issues.apache.org/jira/browse/HDFS-385?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12735106#action_12735106
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Hairong Kuang commented on HDFS-385:
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Sorry for giving comments at this late stage. I was out of the country in the
past few weeks.
1. FsInodeName#getLocalName should return the full path name of the file not
the name of the last component of the path. Better rename the method name to be
getFullPathName. The implementation of this interface in INode should return
the full path name as well. Also to allow FsInodeName to be able to return more
information about a file in the future, better change the interface name to be
FsInodeInfo.
2. FsInodeName should also be a parameter to verifyBlockPlacement and
isValidMove. This makes the interface consistent and makes it easier to get a
file name for a placement policy like colocation.
3. Would it provide better readability if the name of the class
BlockPlacementPolicyDefault is changed to
FirstLocalTwoRemoteBlockPlacementPolicy?
4. For the default policy, isValidDelete should not be empty. It should
implement the deletion policy in trunk. So other placement policy can override
the default deletion policy.
5. Even with the inValidMove API, the default balancer does not work with the
colocation placement policy because it moves one block a time. I'd like to
propose to remove isValidMove API until we could figure out a general balancer
implementation. For this round, the default balancer could check with NameNode
in the very beginning if NameNode runs the default block placement policy. If
no, it stops to run.
> Design a pluggable interface to place replicas of blocks in HDFS
> ----------------------------------------------------------------
>
> Key: HDFS-385
> URL: https://issues.apache.org/jira/browse/HDFS-385
> Project: Hadoop HDFS
> Issue Type: Improvement
> Reporter: dhruba borthakur
> Assignee: dhruba borthakur
> Fix For: 0.21.0
>
> Attachments: BlockPlacementPluggable.txt,
> BlockPlacementPluggable2.txt, BlockPlacementPluggable3.txt,
> BlockPlacementPluggable4.txt, BlockPlacementPluggable4.txt,
> BlockPlacementPluggable5.txt
>
>
> The current HDFS code typically places one replica on local rack, the second
> replica on remote random rack and the third replica on a random node of that
> remote rack. This algorithm is baked in the NameNode's code. It would be nice
> to make the block placement algorithm a pluggable interface. This will allow
> experimentation of different placement algorithms based on workloads,
> availability guarantees and failure models.
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