org.apache.hadoop.mapreduce.lib.input

类 NLineInputFormat

java.lang.Object

org.apache.hadoop.mapreduce.InputFormat<K,V>

org.apache.hadoop.mapreduce.lib.input.FileInputFormat<LongWritable,Text>

org.apache.hadoop.mapreduce.lib.input.NLineInputFormat

@InterfaceAudience.Public
@InterfaceStability.Stable
public class NLineInputFormat
extends FileInputFormat<LongWritable,Text>

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.

嵌套类概要

从类继承的嵌套类/接口 org.apache.hadoop.mapreduce.lib.input.FileInputFormat

FileInputFormat.Counter

字段概要

字段

限定符和类型	字段和说明
static String	LINES_PER_MAP

构造器概要

构造器

构造器和说明
NLineInputFormat()

方法概要

方法

限定符和类型	方法和说明
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>	createRecordReader(InputSplit genericSplit, TaskAttemptContext context) Create a record reader for a given split.
static int	getNumLinesPerSplit(JobContext job) Get the number of lines per split
List<InputSplit>	getSplits(JobContext job) Logically splits the set of input files for the job, splits N lines of the input as one split.
static List<FileSplit>	getSplitsForFile(FileStatus status, Configuration conf, int numLinesPerSplit)
static void	setNumLinesPerSplit(Job job, int numLines) Set the number of lines per split

从类继承的方法 org.apache.hadoop.mapreduce.lib.input.FileInputFormat

addInputPath, addInputPaths, computeSplitSize, getBlockIndex, getFormatMinSplitSize, getInputPathFilter, getInputPaths, getMaxSplitSize, getMinSplitSize, isSplitable, listStatus, setInputPathFilter, setInputPaths, setInputPaths, setMaxInputSplitSize, setMinInputSplitSize

从类继承的方法 java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

字段详细资料

LINES_PER_MAP

public static final String LINES_PER_MAP

另请参阅:

常量字段值

构造器详细资料

NLineInputFormat

public NLineInputFormat()

方法详细资料

createRecordReader

public RecordReader<LongWritable,Text> createRecordReader(InputSplit genericSplit,
                                                 TaskAttemptContext context)
                                                   throws IOException

从类复制的说明: InputFormat

Create a record reader for a given split. The framework will call RecordReader.initialize(InputSplit, TaskAttemptContext) before the split is used.

指定者:

createRecordReader 在类中 InputFormat<LongWritable,Text>

参数:

genericSplit - the split to be read

context - the information about the task

返回:

a new record reader

抛出:

IOException

getSplits

public List<InputSplit> getSplits(JobContext job)
                           throws IOException

Logically splits the set of input files for the job, splits N lines of the input as one split.

覆盖:

getSplits 在类中 FileInputFormat<LongWritable,Text>

参数:

job - job configuration.

返回:

an array of InputSplits for the job.

抛出:

IOException

另请参阅:

FileInputFormat.getSplits(JobContext)

getSplitsForFile

public static List<FileSplit> getSplitsForFile(FileStatus status,
                               Configuration conf,
                               int numLinesPerSplit)
                                        throws IOException

抛出:

IOException

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.

参数:

fileName - Path of file

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

length - number of bytes in InputSplit

返回:

FileSplit

setNumLinesPerSplit

public static void setNumLinesPerSplit(Job job,
                       int numLines)

Set the number of lines per split

参数:

job - the job to modify

numLines - the number of lines per split

getNumLinesPerSplit

public static int getNumLinesPerSplit(JobContext job)

Get the number of lines per split

参数:

job - the job

返回:

the number of lines per split