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From "Tsz Wo (Nicholas), SZE (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-385) Design a pluggable interface to place replicas of blocks in HDFS
Date Wed, 01 Aug 2012 10:25:03 GMT

    [ https://issues.apache.org/jira/browse/HDFS-385?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13426495#comment-13426495
] 

Tsz Wo (Nicholas), SZE commented on HDFS-385:
---------------------------------------------

Thanks for the update.  Some comments:

- Add "srcPath" as a parameter of FSNamesystem.chooseDatanode(..) and then pass "path" in
NamenodeWebHdfsMethods.chooseDatanode(..).

- Add the following comments to FSNamesystem.computeReplicationWorkForBlock(..) as in the
original patch.
{code}
     // choose replication targets: NOT HOLDING THE GLOBAL LOCK
+    // It is costly to extract the filename for which chooseTargets is called,
+    // so for now we pass in the Inode itself.
{code}

- Please remove the tabs since we do not use tabs in Hadoop.  Indentation is two spaces.

Please also run all the unit tests (ant test-core) since Jenkins doesn't work for branch-1.
 Thanks!
                
> 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,
BlockPlacementPluggable6.txt, BlockPlacementPluggable7.txt, blockplacementpolicy-branch-1-win.patch,
blockplacementpolicy-branch-1.patch, blockplacementpolicy2-branch-1-win.patch, blockplacementpolicy2-branch-1.patch,
rat094.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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