org.apache.pig.Accumulator Maven / Gradle / Ivy
/*
* 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 {
/**
* 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();
}