Class NLineInputFormat

  extended by org.apache.hadoop.mapred.FileInputFormat<LongWritable,Text>
      extended by org.apache.hadoop.mapred.lib.NLineInputFormat
All Implemented Interfaces:
InputFormat<LongWritable,Text>, JobConfigurable

public class NLineInputFormat
extends FileInputFormat<LongWritable,Text>
implements JobConfigurable

NLineInputFormat which splits N lines of input as one split. In many "pleasantly" parallel applications, each process/mapper processes the same input file (s), but with computations are controlled by different parameters.(Referred to as "parameter sweeps"). One way to achieve this, is to specify a set of parameters (one set per line) as input in a control file (which is the input path to the map-reduce application, where as the input dataset is specified via a config variable in JobConf.). The NLineInputFormat can be used in such applications, that splits the input file such that by default, one line is fed as a value to one map task, and key is the offset. i.e. (k,v) is (LongWritable, Text). The location hints will span the whole mapred cluster.

Field Summary
Fields inherited from class org.apache.hadoop.mapred.FileInputFormat
Constructor Summary
Method Summary
 void configure(JobConf conf)
          Initializes a new instance from a JobConf.
protected static FileSplit createFileSplit(Path fileName, long begin, long length)
          NLineInputFormat uses LineRecordReader, which always reads (and consumes) at least one character out of its upper split boundary.
 RecordReader<LongWritable,Text> getRecordReader(InputSplit genericSplit, JobConf job, Reporter reporter)
          Get the RecordReader for the given InputSplit.
 InputSplit[] getSplits(JobConf job, int numSplits)
          Logically splits the set of input files for the job, splits N lines of the input as one split.
Methods inherited from class org.apache.hadoop.mapred.FileInputFormat
addInputPath, addInputPathRecursively, addInputPaths, computeSplitSize, getBlockIndex, getInputPathFilter, getInputPaths, getSplitHosts, isSplitable, listStatus, makeSplit, makeSplit, setInputPathFilter, setInputPaths, setInputPaths, setMinSplitSize
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail


public NLineInputFormat()
Method Detail


public RecordReader<LongWritable,Text> getRecordReader(InputSplit genericSplit,
                                                       JobConf job,
                                                       Reporter reporter)
                                                throws IOException
Description copied from interface: InputFormat
Get the RecordReader for the given InputSplit.

It is the responsibility of the RecordReader to respect record boundaries while processing the logical split to present a record-oriented view to the individual task.

Specified by:
getRecordReader in interface InputFormat<LongWritable,Text>
Specified by:
getRecordReader in class FileInputFormat<LongWritable,Text>
genericSplit - the InputSplit
job - the job that this split belongs to
a RecordReader


public InputSplit[] getSplits(JobConf job,
                              int numSplits)
                       throws IOException
Logically splits the set of input files for the job, splits N lines of the input as one split.

Specified by:
getSplits in interface InputFormat<LongWritable,Text>
getSplits in class FileInputFormat<LongWritable,Text>
job - job configuration.
numSplits - the desired number of splits, a hint.
an array of InputSplits for the job.
See Also:
FileInputFormat.getSplits(JobConf, int)


public void configure(JobConf conf)
Description copied from interface: JobConfigurable
Initializes a new instance from a JobConf.

Specified by:
configure in interface JobConfigurable
conf - the configuration


protected static FileSplit createFileSplit(Path fileName,
                                           long begin,
                                           long length)
NLineInputFormat uses LineRecordReader, which always reads (and consumes) at least one character out of its upper split boundary. So to make sure that each mapper gets N lines, we move back the upper split limits of each split by one character here.

fileName - Path of file
begin - the position of the first byte in the file to process
length - number of bytes in InputSplit

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