[jira] [Created] (MAPREDUCE-5572) Provide alternative logic for getPos() implementation in custom RecordReader

["jay vyas (JIRA)" <ji...@apache.org>]

jay vyas created MAPREDUCE-5572:
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             Summary: Provide alternative logic for getPos() implementation in custom RecordReader
                 Key: MAPREDUCE-5572
                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-5572
             Project: Hadoop Map/Reduce
          Issue Type: Bug
          Components: examples
    Affects Versions: 1.2.1, 1.2.0, 1.1.1, 1.1.0, 1.1.3, 1.2.2
            Reporter: jay vyas
            Priority: Minor


The custom RecordReader class defines the getPos() as follows:

long currentOffset = currentStream == null ? 0 : currentStream.getPos();
...

This is meant to prevent errors when underlying stream is null. But it doesn't gaurantee to work: The RawLocalFileSystem, for example, currectly will close the underlying file stream once it is consumed, and the currentStream will thus throw a NullPointerException when trying to access the null stream.

This is only seen when running this in the context where the MapTask class, which is only relevant in mapred.* API, calls getPos() twice in tandem, before and after reading a record.

This custom record reader should be gaurded, or else eliminated, since it assumes something which is not in the FileSystem contract:  That a getPos will always return a integral value.



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