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From "Kai Zheng (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MAPREDUCE-6729) Hitting performance and error when lots of files to write or read
Date Thu, 07 Jul 2016 13:16:11 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-6729?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15366074#comment-15366074

Kai Zheng commented on MAPREDUCE-6729:

Thanks [~mingleizhang] for the reporting and contribution! It sounds good. 

[~ozawa], could you help take a look? This was found in a benchmark test we performed some
time ago. Thanks!

> Hitting performance and error when lots of files to write or read
> -----------------------------------------------------------------
>                 Key: MAPREDUCE-6729
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-6729
>             Project: Hadoop Map/Reduce
>          Issue Type: Improvement
>          Components: benchmarks, performance, test
>            Reporter: mingleizhang
>            Assignee: mingleizhang
>            Priority: Minor
>              Labels: performance, test
>         Attachments: MR-6729.txt
> When doing DFSIO test as a distributed i/o benchmark tool. Then especially writes plenty
of files to disk or read from, both can cause performance issue and imprecise value in a way.
The question is that existing practices needs to delete files when before running a job and
that will cause extra time consumption and furthermore cause performance issue, statistical
time error and imprecise throughput while the files are lots of. So we need to replace or
improve this hack to prevent this from happening in the future.
> {code}
> public static void testWrite() throws Exception {
>     FileSystem fs = cluster.getFileSystem();
>     long tStart = System.currentTimeMillis();
>     bench.writeTest(fs); // this line of code will cause extra time consumption because
of fs.delete(*,*) by the writeTest method
>     long execTime = System.currentTimeMillis() - tStart;
>     bench.analyzeResult(fs, TestType.TEST_TYPE_WRITE, execTime);
>   }
> private void writeTest(FileSystem fs) throws IOException {
>   Path writeDir = getWriteDir(config);
>   fs.delete(getDataDir(config), true);
>   fs.delete(writeDir, true);    
>   runIOTest(WriteMapper.class, writeDir);
>   }
> {code} 
> [https://github.com/apache/hadoop/blob/trunk/hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-jobclient/src/test/java/org/apache/hadoop/fs/TestDFSIO.java]

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