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From "Hadoop QA (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-1480) All replicas for a block with repl=2 end up in same rack
Date Sat, 20 Aug 2011 00:49:29 GMT

    [ https://issues.apache.org/jira/browse/HDFS-1480?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13088095#comment-13088095
] 

Hadoop QA commented on HDFS-1480:
---------------------------------

-1 overall.  Here are the results of testing the latest attachment 
  http://issues.apache.org/jira/secure/attachment/12491018/hdfs-1480.txt
  against trunk revision .

    +1 @author.  The patch does not contain any @author tags.

    +1 tests included.  The patch appears to include 3 new or modified tests.

    +1 javadoc.  The javadoc tool did not generate any warning messages.

    +1 javac.  The applied patch does not increase the total number of javac compiler warnings.

    +1 findbugs.  The patch does not introduce any new Findbugs (version 1.3.9) warnings.

    +1 release audit.  The applied patch does not increase the total number of release audit
warnings.

    -1 core tests.  The patch failed these core unit tests:


    +1 contrib tests.  The patch passed contrib unit tests.

    +1 system test framework.  The patch passed system test framework compile.

Test results: https://builds.apache.org/job/PreCommit-HDFS-Build/1133//testReport/
Findbugs warnings: https://builds.apache.org/job/PreCommit-HDFS-Build/1133//artifact/trunk/target/newPatchFindbugsWarnings.html
Console output: https://builds.apache.org/job/PreCommit-HDFS-Build/1133//console

This message is automatically generated.

> All replicas for a block with repl=2 end up in same rack
> --------------------------------------------------------
>
>                 Key: HDFS-1480
>                 URL: https://issues.apache.org/jira/browse/HDFS-1480
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: name-node
>    Affects Versions: 0.20.2
>            Reporter: T Meyarivan
>            Assignee: Todd Lipcon
>             Fix For: 0.23.0
>
>         Attachments: hdfs-1480-test.txt, hdfs-1480.txt, hdfs-1480.txt, hdfs-1480.txt
>
>
> It appears that all replicas of a block can end up in the same rack. The likelihood of
such replicas seems to be directly related to decommissioning of nodes. 
> Post rolling OS upgrade (decommission 3-10% of nodes, re-install etc, add them back)
of a running cluster, all replicas of about 0.16% of blocks ended up in the same rack.
> Hadoop Namenode UI etc doesn't seem to know about such incorrectly replicated blocks.
"hadoop fsck .." does report that the blocks must be replicated on additional racks.
> Looking at ReplicationTargetChooser.java, following seem suspect:
> snippet-01:
> {code}
>     int maxNodesPerRack =
>       (totalNumOfReplicas-1)/clusterMap.getNumOfRacks()+2;
> {code}
> snippet-02:
> {code}
>       case 2:
>         if (clusterMap.isOnSameRack(results.get(0), results.get(1))) {
>           chooseRemoteRack(1, results.get(0), excludedNodes,
>                            blocksize, maxNodesPerRack, results);
>         } else if (newBlock){
>           chooseLocalRack(results.get(1), excludedNodes, blocksize,
>                           maxNodesPerRack, results);
>         } else {
>           chooseLocalRack(writer, excludedNodes, blocksize,
>                           maxNodesPerRack, results);
>         }
>         if (--numOfReplicas == 0) {
>           break;
>         }
> {code}
> snippet-03:
> {code}
>     do {
>       DatanodeDescriptor[] selectedNodes =
>         chooseRandom(1, nodes, excludedNodes);
>       if (selectedNodes.length == 0) {
>         throw new NotEnoughReplicasException(
>                                              "Not able to place enough replicas");
>       }
>       result = (DatanodeDescriptor)(selectedNodes[0]);
>     } while(!isGoodTarget(result, blocksize, maxNodesPerRack, results));
> {code}

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