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org.apache.crunch.lib.join
Class MapsideJoinStrategy<K,U,V>

java.lang.Object
  org.apache.crunch.lib.join.MapsideJoinStrategy<K,U,V>

All Implemented Interfaces:

Serializable, JoinStrategy<K,U,V>

public class MapsideJoinStrategy<K,U,V>
extends Object
implements JoinStrategy<K,U,V>

Utility for doing map side joins on a common key between two PTables.

A map side join is an optimized join which doesn't use a reducer; instead, the right side of the join is loaded into memory and the join is performed in a mapper. This style of join has the important implication that the output of the join is not sorted, which is the case with a conventional (reducer-based) join.

See Also:

Serialized Form

Constructor Summary

MapsideJoinStrategy()
Constructs a new instance of the MapsideJoinStratey, materializing the right-side join table to disk before the join is performed.

MapsideJoinStrategy(boolean materialize)
Constructs a new instance of the MapsideJoinStrategy.

Method Summary

PTable<K,Pair<U,V>>

join(PTable<K,U> left, PTable<K,V> right, JoinType joinType) Join two tables with the given join type.

Methods inherited from class java.lang.Object

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

Constructor Detail

MapsideJoinStrategy

public MapsideJoinStrategy()

Constructs a new instance of the MapsideJoinStratey, materializing the right-side join table to disk before the join is performed.

MapsideJoinStrategy

public MapsideJoinStrategy(boolean materialize)

Constructs a new instance of the MapsideJoinStrategy. If the materialize} argument is true, then the right-side join PTable will be materialized to disk before the in-memory join is performed. If it is false, then Crunch can optionally read and process the data from the right-side table without having to run a job to materialize the data to disk first.

Parameters:

materialize - Whether or not to materialize the right-side table before the join

Method Detail

join

public PTable<K,Pair<U,V>> join(PTable<K,U> left,
                                PTable<K,V> right,
                                JoinType joinType)

Description copied from interface: JoinStrategy

Join two tables with the given join type.

Specified by:

join in interface JoinStrategy<K,U,V>

Parameters:

left - left table to be joined

right - right table to be joined

joinType - type of join to perform

Returns:

joined tables