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From "Hong Tang (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HDFS-385) Design a pluggable interface to place replicas of blocks in HDFS
Date Tue, 07 Jul 2009 00:59:14 GMT

    [ https://issues.apache.org/jira/browse/HDFS-385?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12727855#action_12727855
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Hong Tang commented on HDFS-385:
--------------------------------

Some minor nits:
- In class BlockPlacementPolicy, the javadoc for chooseTarget contains an unused parameter
excludedNodes. 
- There are two versions of abstract chooseTarget(), is it possible to provide a default implementation
for chooseTarget(FSInodeName srcInode, int numOfReplicas, DatanodeDescriptor writer,  List<DatanodeDescriptor>
chosenNodes, long blocksize) on top of chooseTarget(String srcPath, int numOfReplicas, DatanodeDescriptor
writer,  List<DatanodeDescriptor> chosenNodes, long blocksize) ?
-  There is asymmetry for chooseTarget which takes a list of DatanodeDescriptor and returns
an array of DatanodeDescriptor. Why not returning a List too?

> 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
>
>
> 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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