Package org.apache.hadoop.mapred.lib

Class NLineInputFormat

java.lang.Object

org.apache.hadoop.mapred.FileInputFormat<LongWritable,Text>

org.apache.hadoop.mapred.lib.NLineInputFormat

All Implemented Interfaces:

InputFormat<LongWritable,Text>, JobConfigurable

@Public
@Stable
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.

Nested Class Summary

Nested classes/interfaces inherited from class org.apache.hadoop.mapred.FileInputFormat

FileInputFormat.Counter

Field Summary

Fields inherited from class org.apache.hadoop.mapred.FileInputFormat

INPUT_DIR_NONRECURSIVE_IGNORE_SUBDIRS, INPUT_DIR_RECURSIVE, LOG, NUM_INPUT_FILES

Constructor Summary

Constructors

Constructor	Description
NLineInputFormat()

Method Summary

Modifier and Type	Method	Description
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 Details

NLineInputFormat

public NLineInputFormat()

Method Details

getRecordReader

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>

Parameters:

genericSplit - the InputSplit

job - the job that this split belongs to

Returns:

a RecordReader

Throws:

IOException

getSplits

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>

Overrides:

getSplits in class FileInputFormat<LongWritable,Text>

Parameters:

job - job configuration.

numSplits - the desired number of splits, a hint.

Returns:

an array of InputSplits for the job.

Throws:

IOException

See Also:

• FileInputFormat.getSplits(JobConf, int)

configure

public void configure(JobConf conf)

Description copied from interface: JobConfigurable

Initializes a new instance from a JobConf.

Specified by:

configure in interface JobConfigurable

Parameters:

conf - the configuration

createFileSplit

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.

Parameters:

fileName - Path of file

begin - the position of the first byte in the file to process

length - number of bytes in InputSplit

Returns:

FileSplit