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Date: Mon, 18 Apr 2016 13:11:25 +0000 (UTC)
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Subject: [jira] [Commented] (HDFS-10275) TestDataNodeMetrics failing
 intermittently due to TotalWriteTime counted incorrectly
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    [ https://issues.apache.org/jira/browse/HDFS-10275?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15245624#comment-15245624 ] 

Hudson commented on HDFS-10275:
-------------------------------

FAILURE: Integrated in Hadoop-trunk-Commit #9626 (See [https://builds.apache.org/job/Hadoop-trunk-Commit/9626/])
HDFS-10275. TestDataNodeMetrics failing intermittently due to (waltersu4549: rev ab903029a9d353677184ff5602966b11ffb408b9)
* hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/TestDataNodeMetrics.java


> TestDataNodeMetrics failing intermittently due to TotalWriteTime counted incorrectly
> ------------------------------------------------------------------------------------
>
>                 Key: HDFS-10275
>                 URL: https://issues.apache.org/jira/browse/HDFS-10275
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: test
>            Reporter: Lin Yiqun
>            Assignee: Lin Yiqun
>             Fix For: 2.7.3
>
>         Attachments: HDFS-10275.001.patch
>
>
> The unit test {{TestDataNodeMetrics}} fails intermittently. The failed info show these:
> {code}
> Results :
> Failed tests: 
>   TestDataNodeVolumeFailureToleration.testVolumeAndTolerableConfiguration:195->testVolumeConfig:232 expected:<false> but was:<true>
> Tests in error: 
>   TestOpenFilesWithSnapshot.testWithCheckpoint:94 ? IO Timed out waiting for Min...
>   TestDataNodeMetrics.testDataNodeTimeSpend:279 ? Timeout Timed out waiting for ...
>   TestHFlush.testHFlushInterrupted ? IO The stream is closed
> {code}
> In line 279 in {{TestDataNodeMetrics}}, it takes place timed out. Then I looked into the code and found the real reason is that the metric of {{TotalWriteTime}} frequently count 0 in each iteration of creating file. And the this leads to retry operations till timeout.
> I debug the test in my local. I found the most suspect reason which cause {{TotalWriteTime}} metric count always be 0 is that we using the {{SimulatedFSDataset}} for spending time test. In {{SimulatedFSDataset}}, it will use the inner class's method {{SimulatedOutputStream#write}} to count the write time and the method of this class just updates the {{length}} and throws its data away.
> {code}
>     @Override
>     public void write(byte[] b,
>               int off,
>               int len) throws IOException  {
>       length += len;
>     }
> {code} 
> So the writing operation hardly not costs any time. So we should use a real way to create file instead of simulated way. I have tested in my local that the test is passed just one time when I delete the simulated way, while the test retries many times to count write time in old way.



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