?? partitioner.java
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/** * Copyright 2005 The Apache Software Foundation * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */package org.apache.hadoop.mapred;import org.apache.hadoop.io.Writable;import org.apache.hadoop.io.WritableComparable;/** Partitions the key space. A partition is created for each reduce task. */public interface Partitioner extends JobConfigurable { /** Returns the paritition number for a given entry given the total number of * partitions. Typically a hash function on a all or a subset of the key. * * @param key the entry key * @param value the entry value * @param numPartitions the number of partitions * @return the partition number */ int getPartition(WritableComparable key, Writable value, int numPartitions);}
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