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Posted to mapreduce-dev@hadoop.apache.org by "Victor Zhang (Jira)" <ji...@apache.org> on 2019/08/20 09:10:00 UTC
[jira] [Created] (MAPREDUCE-7233) MapReduce Input Path Should
Ignore Path Ends With '/*' When Job Submit
Victor Zhang created MAPREDUCE-7233:
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Summary: MapReduce Input Path Should Ignore Path Ends With '/*' When Job Submit
Key: MAPREDUCE-7233
URL: https://issues.apache.org/jira/browse/MAPREDUCE-7233
Project: Hadoop Map/Reduce
Issue Type: Improvement
Components: job submission, performance
Affects Versions: 2.7.2
Reporter: Victor Zhang
Attachments: job submit.jpg
We have a public and shared hadoop cluster that runs so many MR job from different department.
I found that job submission very slow once the input path of the job set to a path ends with "/*", like "/my/path/*", but "/my/path" or "/my/path/" works fine.
After read the code. I think the problem lies in the process of splits calculation.
FileInputFormat#singleThreadedListStatus() method get a array of FileStatus first. If the input path ends with "/*", and the result is all file/directory FileStatus object in the input path. But only one FileStatus object(the input path) if the input path not ends with "/*".
The next step is find the LocatedFileStatus of each FileStatus object. so, only the directory FileStatus do searching the LocatedFileStatus(dfs.listPaths(), batch).
Finally, when calculate job split like FileInputFormat#getSplits() method. If the FileStatus is not LocatedFileStatus object, then use fs.getFileBlockLocations() method to fetch. Which could lead a lot of RPC requests when many files in the input path. CombineFileInputFormat do this also in the construction method of OneFileInfo.
So, in this case, some job take a few minutes/hours to submit.
I tried to remove the suffix of the input path that ends with "/*" before the code that get file status, but I don't confirm if this will cause other problems.
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