/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you 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 com.aliyun.odps.mapred;
import com.aliyun.odps.data.Record;
import com.aliyun.odps.mapred.conf.JobConf;
/**
* 分区类，决定 {@link Mapper} 写出的中间结果（键值对）输出给哪个 {@link Reducer} .
*
* 可以通过{@link JobConf#setPartitionerClass(Class)}方法自定义分区类，否则会使用分区列：
* {@link JobConf#setPartitionColumns(String[])}
*
* 注意：当用户同时指定{@link JobConf#setPartitionerClass(Class)}和{@link JobConf#setPartitionColumns(String[])}时，用户行为未定义。
*
* @see Mapper
* @see Reducer
*/
public abstract class Partitioner {
/**
* 此方法会在分区类对象被new出来后立即调用，传入运行时的{@link JobConf}对象
*
* @param job
* 运行时的JobConf对象
*/
public void configure(JobConf job) {
}
;
/**
* 给定Key/Value和分区数（numPartitions），计算该Key/Value输出到哪个分区（分区索引从0到numPartitions-1），
* 这里分区数（numPartitions）就是Reduce个数
*
* <p>
* 此方法通常实现为对key的某个哈希函数，可以参考
* {@link HashPartitioner#getPartition(Object, Object, int)}的实现
* </p>
*
* @param key
* 待分区的Key
* @param value
* 待分区的Value
* @param numPartitions
* 分区数，既Reduce个数
* @return 范围从0到numPartitions-1的分区索引
*/
public abstract int getPartition(Record key, Record value, int numPartitions);
}