[jira] Created: (MAPREDUCE-1176) Contribution: FixedLengthInputFormat and FixedLengthRecordReader

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

Contribution: FixedLengthInputFormat and FixedLengthRecordReader
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                 Key: MAPREDUCE-1176
                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-1176
             Project: Hadoop Map/Reduce
          Issue Type: New Feature
    Affects Versions: 0.20.1
         Environment: Any
            Reporter: BitsOfInfo
            Priority: Minor


Hello,
I would like to contribute the following two classes for incorporation into the mapreduce.lib.input package. These two classes can be used when you need to read data from files containing fixed length (fixed width) records. Such files have no CR/LF (or any combination thereof), no delimiters etc, but each record is a fixed length, and extra data is padded with spaces. The data is one gigantic line within a file.

Provided are two classes first is the FixedLengthInputFormat and its corresponding FixedLengthRecordReader. When creating a job that specifies this input format, the job must have the "mapreduce.input.fixedlengthinputformat.record.length" property set as follows

myJobConf.setInt("mapreduce.input.fixedlengthinputformat.record.length",[myFixedRecordLength]);

OR

myJobConf.setInt(FixedLengthInputFormat.FIXED_RECORD_LENGTH, [myFixedRecordLength]);

This input format overrides computeSplitSize() in order to ensure that InputSplits do not contain any partial records since with fixed records there is no way to determine where a record begins if that were to occur. Each InputSplit passed to the FixedLengthRecordReader will start at the beginning of a record, and the last byte in the InputSplit will be the last byte of a record. The override of computeSplitSize() delegates to FileInputFormat's compute method, and then adjusts the returned split size by doing the following: (Math.floor(fileInputFormatsComputedSplitSize / fixedRecordLength) * fixedRecordLength)

This suite of fixed length input format classes, does not support compressed files. 

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