kyotocabinet

Class MapReduce

Object

MapReduce

public abstract class MapReduce
extends Object

MapReduce framework.

Field Summary

Fields

Modifier and Type	Field and Description
static int	XNOCOMP execution option: avoid compression of temporary databases
static int	XNOLOCK execution option: avoid locking against update operations

Constructor Summary

Constructors

Constructor and Description
MapReduce()

Method Summary

Methods

Modifier and Type	Method and Description
protected boolean	emit(byte[] key, byte[] value) Emit a record from the mapper.
boolean	execute(DB db, String tmppath, int opts) Execute the MapReduce process about a database.
boolean	log(String name, String message) Process a log message.
abstract boolean	map(byte[] key, byte[] value) Map a record data.
boolean	midprocess() Mediate between the map and the reduce phases.
boolean	postprocess() Postprocess the reduce operations.
boolean	preprocess() Preprocess the map operations.
abstract boolean	reduce(byte[] key, ValueIterator iter) Reduce a record data.

Methods inherited from class Object

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

Field Detail

XNOCOMP

public static final int XNOCOMP

execution option: avoid compression of temporary databases

See Also:

Constant Field Values

XNOLOCK

public static final int XNOLOCK

execution option: avoid locking against update operations

See Also:

Constant Field Values

Constructor Detail

MapReduce

public MapReduce()

Method Detail

emit

protected boolean emit(byte[] key,
           byte[] value)

Emit a record from the mapper.

Parameters:

key - specifies the key.

value - specifies the value.

Returns:

true on success, or false on failure.

execute

public boolean execute(DB db,
              String tmppath,
              int opts)

Execute the MapReduce process about a database.

Parameters:

db - the source database.

tmppath - the path of a directory for the temporary data storage. If it is an empty string, temporary data are handled on memory.

opts - the optional features by bitwise-or: MapReduce::XNOLOCK to avoid locking against update operations by other threads, MapReduce::XNOCOMP to avoid compression of temporary databases.

Returns:

true on success, or false on failure.

log

public boolean log(String name,
          String message)

Process a log message.

Parameters:

name - the name of the event.

message - a supplement message.

Returns:

true on success, or false on failure.

map

public abstract boolean map(byte[] key,
          byte[] value)

Map a record data.

Parameters:

key - specifies the key.

value - specifies the value.

Returns:

true on success, or false on failure.

Note:

This method can call the MapReduce::emit method to emit a record. To avoid deadlock, any explicit database operation must not be performed in this method.

midprocess

public boolean midprocess()

Mediate between the map and the reduce phases.

Returns:

true on success, or false on failure.

Note:

This method can call the MapReduce::emit method to emit a record. To avoid deadlock, any explicit database operation must not be performed in this method.

postprocess

public boolean postprocess()

Postprocess the reduce operations.

Returns:

true on success, or false on failure.

Note:

To avoid deadlock, any explicit database operation must not be performed in this method.

preprocess

public boolean preprocess()

Preprocess the map operations.

Returns:

true on success, or false on failure.

Note:

This method can call the MapReduce::emit method to emit a record. To avoid deadlock, any explicit database operation must not be performed in this method.

reduce

public abstract boolean reduce(byte[] key,
             ValueIterator iter)

Reduce a record data.

Parameters:

key - specifies the key.

iter - the iterator to get the values.

Returns:

true on success, or false on failure.

Note:

To avoid deadlock, any explicit database operation must not be performed in this method.