org.apache.hadoop.mapred.lib
Class NLineInputFormat

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

@InterfaceAudience.Public
@InterfaceStability.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.


Field Summary
 
Fields inherited from class org.apache.hadoop.mapred.FileInputFormat
LOG, NUM_INPUT_FILES
 
Constructor Summary
NLineInputFormat()
           
 
Method Summary
 void configure(JobConf conf)
          Initializes a new instance from a JobConf.
 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, setInputPathFilter, setInputPaths, setInputPaths, setMinSplitSize
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Constructor Detail

NLineInputFormat

public NLineInputFormat()
Method Detail

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


Copyright © 2012 Apache Software Foundation. All Rights Reserved.