org.terrier.structures.indexing.singlepass.hadoop

Class HadoopRunsMerger

java.lang.Object

org.terrier.structures.indexing.singlepass.RunsMerger

org.terrier.structures.indexing.singlepass.hadoop.HadoopRunsMerger

public class HadoopRunsMerger
extends RunsMerger

This is the main merger class for Hadoop runs. It provides functionality for the merging of lexicons and inverted index shards from the map task indexers.

Since:

2.2

Author:

Richard McCreadie and Craig Macdonald

Nested Class Summary

Nested classes/interfaces inherited from class org.terrier.structures.indexing.singlepass.RunsMerger

RunsMerger.PostingComparator

Field Summary

Fields

Modifier and Type	Field and Description
protected LinkedList<MapData>	mapData The data loaded from side-effect files about each map task
protected int	numReducers Number of Reducers Used

Fields inherited from class org.terrier.structures.indexing.singlepass.RunsMerger

bos, currentTerm, lastDocFreq, lastDocument, lastFreq, lastTermWritten, myRun, numberOfPointers, queue, runsSource, startOffset, termStatistics

Constructor Summary

Constructors

Constructor and Description
HadoopRunsMerger(RunIteratorFactory _runsSource) Constructs an instance of HadoopRunsMerger.

Method Summary

Methods

Modifier and Type	Method and Description
void	beginMerge(LinkedList<MapData> _mapData) Alternate Merge operation for merging a linked list of runs of the form Hadoop_MapData.
void	endMerge(LexiconOutputStream<String> lexStream) Ends the merging phase, writes the last entry and closes the streams.
int	getDocumentOffset(int splitNo, int flushNumber) Get the offset for the document based on a split and flush.
int	getNumReducers() Gets the number of Reducers to Merge for: 1 for single Reducer, >1 for multi-Reducers
void	mergeOne(LexiconOutputStream<String> lexStream) Mergers one term in the runs.
void	setNumReducers(int _numReducers) Sets the number of Reducers to Merge for: 1 for single Reducer, >1 for multi-Reducers

Methods inherited from class org.terrier.structures.indexing.singlepass.RunsMerger

beginMerge, getBitOffset, getBos, getByteOffset, getLastDocFreq, getLastFreq, getLastTermWritten, getNumberOfPointers, getNumberOfTerms, init, init, isDone, setBos, setLastTermWritten

Methods inherited from class java.lang.Object

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

Field Detail

mapData

protected LinkedList<MapData> mapData

The data loaded from side-effect files about each map task

numReducers

protected int numReducers

Number of Reducers Used

Constructor Detail

HadoopRunsMerger

public HadoopRunsMerger(RunIteratorFactory _runsSource)

Constructs an instance of HadoopRunsMerger.

Parameters:

_runsSource -

Method Detail

beginMerge

public void beginMerge(LinkedList<MapData> _mapData)

Alternate Merge operation for merging a linked list of runs of the form Hadoop_MapData. This routine merges the multiple runs created during the map process of hadoop indexing as such it corrects for Document id 'shift' caused by random splitting of runs due to flushing and map splitting.

Parameters:

_mapData - - information about the number of documents per map and run. One element for every map.

Throws:

IOException

endMerge

public void endMerge(LexiconOutputStream<String> lexStream)

Ends the merging phase, writes the last entry and closes the streams.

Overrides:

endMerge in class RunsMerger

Parameters:

lexStream - LexiconOutputStream used to write the lexicon.

mergeOne

public void mergeOne(LexiconOutputStream<String> lexStream)
              throws Exception

Mergers one term in the runs. If a run is exhausted, it is closed and removed from the queue.

Overrides:

mergeOne in class RunsMerger

Parameters:

lexStream - LexiconOutputStream used to write the lexicon.

Throws:

Exception - if an I/O error occurs.

getNumReducers

public int getNumReducers()

Gets the number of Reducers to Merge for: 1 for single Reducer, >1 for multi-Reducers

Returns:

how many reducers are in use.

setNumReducers

public void setNumReducers(int _numReducers)

Sets the number of Reducers to Merge for: 1 for single Reducer, >1 for multi-Reducers

getDocumentOffset

public int getDocumentOffset(int splitNo,
                    int flushNumber)
                      throws IOException

Get the offset for the document based on a split and flush.

Throws:

IOException