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From "Hadoop QA (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-7300) The getMaxNodesPerRack() method in BlockPlacementPolicyDefault is flawed
Date Tue, 28 Oct 2014 20:36:35 GMT

    [ https://issues.apache.org/jira/browse/HDFS-7300?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14187406#comment-14187406

Hadoop QA commented on HDFS-7300:

{color:red}-1 overall{color}.  Here are the results of testing the latest attachment 
  against trunk revision ade3727.

    {color:green}+1 @author{color}.  The patch does not contain any @author tags.

    {color:red}-1 tests included{color}.  The patch doesn't appear to include any new or modified
                        Please justify why no new tests are needed for this patch.
                        Also please list what manual steps were performed to verify this patch.

    {color:green}+1 javac{color}.  The applied patch does not increase the total number of
javac compiler warnings.

    {color:green}+1 javadoc{color}.  There were no new javadoc warning messages.

    {color:green}+1 eclipse:eclipse{color}.  The patch built with eclipse:eclipse.

    {color:green}+1 findbugs{color}.  The patch does not introduce any new Findbugs (version
2.0.3) warnings.

    {color:green}+1 release audit{color}.  The applied patch does not increase the total number
of release audit warnings.

    {color:red}-1 core tests{color}.  The patch failed these unit tests in hadoop-hdfs-project/hadoop-hdfs:


                                      The following test timeouts occurred in hadoop-hdfs-project/hadoop-hdfs:


    {color:green}+1 contrib tests{color}.  The patch passed contrib unit tests.

Test results: https://builds.apache.org/job/PreCommit-HDFS-Build/8572//testReport/
Console output: https://builds.apache.org/job/PreCommit-HDFS-Build/8572//console

This message is automatically generated.

> The getMaxNodesPerRack() method in BlockPlacementPolicyDefault is flawed
> ------------------------------------------------------------------------
>                 Key: HDFS-7300
>                 URL: https://issues.apache.org/jira/browse/HDFS-7300
>             Project: Hadoop HDFS
>          Issue Type: Bug
>            Reporter: Kihwal Lee
>            Assignee: Kihwal Lee
>            Priority: Critical
>         Attachments: HDFS-7300.patch
> The {{getMaxNodesPerRack()}} can produce an undesirable result in some cases.
> - Three replicas on two racks. The max is 3, so everything can go to one rack.
> - Two replicas on two or more racks. The max is 2, both replicas can end up in the same
> {{BlockManager#isNeededReplication()}} fixes this after block/file is closed because
{{blockHasEnoughRacks()}} will return fail.  This is not only extra work, but also can break
the favored nodes feature.
> When there are two racks and two favored nodes are specified in the same rack, NN may
allocate the third replica on a node in the same rack, because {{maxNodesPerRack}} is 3. When
closing the file, NN moves a block to the other rack. There is 66% chance that a favored node
is moved.  If {{maxNodesPerRack}} was 2, this would not happen.

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