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Date: Sun, 13 Dec 2009 21:53:18 +0000 (UTC)
From: "Hadoop QA (JIRA)" <jira@apache.org>
To: hdfs-issues@hadoop.apache.org
Subject: [jira] Commented: (HDFS-767) Job failure due to
 BlockMissingException
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    [ https://issues.apache.org/jira/browse/HDFS-767?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12789950#action_12789950 ] 

Hadoop QA commented on HDFS-767:
--------------------------------

-1 overall.  Here are the results of testing the latest attachment 
  http://issues.apache.org/jira/secure/attachment/12425556/HDFS-767.patch
  against trunk revision 889494.

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

    +1 tests included.  The patch appears to include 6 new or modified tests.

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

    -1 javac.  The applied patch generated 23 javac compiler warnings (more than the trunk's current 22 warnings).

    +1 findbugs.  The patch does not introduce any new Findbugs warnings.

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

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

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

Test results: http://hudson.zones.apache.org/hudson/job/Hdfs-Patch-h5.grid.sp2.yahoo.net/144/testReport/
Findbugs warnings: http://hudson.zones.apache.org/hudson/job/Hdfs-Patch-h5.grid.sp2.yahoo.net/144/artifact/trunk/build/test/findbugs/newPatchFindbugsWarnings.html
Checkstyle results: http://hudson.zones.apache.org/hudson/job/Hdfs-Patch-h5.grid.sp2.yahoo.net/144/artifact/trunk/build/test/checkstyle-errors.html
Console output: http://hudson.zones.apache.org/hudson/job/Hdfs-Patch-h5.grid.sp2.yahoo.net/144/console

This message is automatically generated.

> Job failure due to BlockMissingException
> ----------------------------------------
>
>                 Key: HDFS-767
>                 URL: https://issues.apache.org/jira/browse/HDFS-767
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>            Reporter: Ning Zhang
>            Assignee: Ning Zhang
>         Attachments: HDFS-767.patch
>
>
> If a block is request by too many mappers/reducers (say, 3000) at the same time, a BlockMissingException is thrown because it exceeds the upper limit (I think 256 by default) of number of threads accessing the same block at the same time. The DFSClient wil catch that exception and retry 3 times after waiting for 3 seconds. Since the wait time is a fixed value, a lot of clients will retry at about the same time and a large portion of them get another failure. After 3 retries, there are about 256*4 = 1024 clients got the block. If the number of clients are more than that, the job will fail. 

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