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https://issues.apache.org/jira/browse/HDFS-10275?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15245569#comment-15245569
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Walter Su commented on HDFS-10275:
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sorry I didn't see that. The patch LGTM. +1.
> 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
> 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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