| /* |
| * 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 org.apache.pig; |
| |
| import java.io.IOException; |
| |
| import org.apache.hadoop.io.WritableComparable; |
| import org.apache.hadoop.mapreduce.InputSplit; |
| |
| import org.apache.pig.classification.InterfaceAudience; |
| import org.apache.pig.classification.InterfaceStability; |
| |
| /** |
| * Implementing this interface indicates to Pig that a given loader |
| * can be used for MergeJoin. It does not mean the data itself is ordered, |
| * but rather that the splits returned by the underlying InputFormat |
| * can be ordered to match the order of the data they are loading. For |
| * example, files splits have a natural order (that of the file they are |
| * from) while splits of RDBMS does not (since tables have no inherent order). |
| * The position as represented by the |
| * WritableComparable object is stored in the index created by |
| * a MergeJoin sampling MapReduce job to get an ordered sequence of splits. |
| * It is necessary to read splits in order during a merge join to assure |
| * data is being read according to the sort order. |
| * @since Pig 0.7 |
| */ |
| @InterfaceAudience.Public |
| @InterfaceStability.Evolving // Since we haven't done outer join for merge join yet |
| public interface OrderedLoadFunc { |
| |
| /** |
| * The WritableComparable object returned will be used to compare |
| * the position of different splits in an ordered stream |
| * @param split An InputSplit from the InputFormat underlying this loader. |
| * @return WritableComparable representing the position of the split in input |
| * @throws IOException |
| */ |
| public WritableComparable<?> getSplitComparable(InputSplit split) |
| throws IOException; |
| |
| } |