[jira] [Created] (HADOOP-16147) Allow CopyListing sequence file keys and values to be more easily customized

["Andrew Olson (JIRA)" <ji...@apache.org>]

Andrew Olson created HADOOP-16147:
-------------------------------------

             Summary: Allow CopyListing sequence file keys and values to be more easily customized
                 Key: HADOOP-16147
                 URL: https://issues.apache.org/jira/browse/HADOOP-16147
             Project: Hadoop Common
          Issue Type: Improvement
          Components: tools/distcp
            Reporter: Andrew Olson


We have encountered a scenario where, when using the Crunch library to run a distributed copy (CRUNCH-660, CRUNCH-675) at the conclusion of a job we need to dynamically rename target paths to the preferred destination output part file names, rather than retaining the original source path names.

A custom CopyListing implementation appears to be the proper solution for this. However the place where the current SimpleCopyListing logic needs to be adjusted is in a private method (writeToFileListing), so a relatively large portion of the class would need to be cloned.

To minimize the amount of code duplication required for such a custom implementation, we propose adding two new protected methods to the CopyListing class, that can be used to change the actual keys and/or values written to the copy listing sequence file: 

{noformat}
protected Text getFileListingKey(Path sourcePathRoot, CopyListingFileStatus fileStatus);

protected CopyListingFileStatus getFileListingValue(CopyListingFileStatus fileStatus);
{noformat}

The SimpleCopyListing class would then be modified to consume these methods as follows,
{noformat}
fileListWriter.append(
   getFileListingKey(sourcePathRoot, fileStatus),
   getFileListingValue(fileStatus));
{noformat}

The default implementations would simply preserve the present behavior of the SimpleCopyListing class, and could reside in either CopyListing or SimpleCopyListing, whichever is preferable.

{noformat}
protected Text getFileListingKey(Path sourcePathRoot, CopyListingFileStatus fileStatus) {
   return new Text(DistCpUtils.getRelativePath(sourcePathRoot, fileStatus.getPath()));
}

protected CopyListingFileStatus getFileListingValue(CopyListingFileStatus fileStatus) {
   return fileStatus;
}
{noformat}

Please let me know if this proposal seems to be on the right track. If so I can provide a patch.



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