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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