| /* |
| * 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.pig.classification.InterfaceAudience; |
| import org.apache.pig.classification.InterfaceStability; |
| import org.apache.pig.data.Tuple; |
| |
| /** |
| * An interface that allows UDFs that take a bag to accumulate tuples in chunks rather than take |
| * the whole set at once. This is intended for UDFs that do not need to see all of the tuples |
| * together but cannot be used with the combiner. This lowers the memory needs, avoiding the need |
| * to spill large bags, and thus speeds up the query. An example is something like session analysis. |
| * It cannot be used with the combiner because all it's inputs must first be ordered. But it does |
| * not need to see all the tuples at once. UDF implementors might also choose to implement this |
| * interface so that if other UDFs in the FOREACH implement it it can be used. |
| * @since Pig 0.6 |
| */ |
| @InterfaceAudience.Public |
| @InterfaceStability.Stable |
| public interface Accumulator <T> { |
| /** |
| * Pass tuples to the UDF. |
| * @param b A tuple containing a single field, which is a bag. The bag will contain the set |
| * of tuples being passed to the UDF in this iteration. |
| */ |
| public void accumulate(Tuple b) throws IOException; |
| |
| /** |
| * Called when all tuples from current key have been passed to accumulate. |
| * @return the value for the UDF for this key. |
| */ |
| public T getValue(); |
| |
| /** |
| * Called after getValue() to prepare processing for next key. |
| */ |
| public void cleanup(); |
| } |