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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (FLINK-1293) Add support for out-of-place aggregations
Date Mon, 01 Dec 2014 13:05:13 GMT

    [ https://issues.apache.org/jira/browse/FLINK-1293?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14229761#comment-14229761
] 

ASF GitHub Bot commented on FLINK-1293:
---------------------------------------

Github user fhueske commented on a diff in the pull request:

    https://github.com/apache/incubator-flink/pull/243#discussion_r21087064
  
    --- Diff: flink-java/src/main/java/org/apache/flink/api/java/aggregation/AggregationMapIntermediateUdf.java
---
    @@ -0,0 +1,65 @@
    +/*
    + * 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.flink.api.java.aggregation;
    +
    +import org.apache.flink.api.common.functions.MapFunction;
    +import org.apache.flink.api.java.tuple.Tuple;
    +
    +/**
    + * Map UDF that maps input tuples to an intermediate tuple on which the
    + * aggregation is performed.
    + * 
    + * <p>
    + * For each aggregation function {@code initializeIntermediate}
    + * is called with the value of the input tuple at the input
    + * position of the aggregation function.
    + * 
    + * @param <IN> Type of the intermediate tuple.
    + * @param <OUT> Aggregation output type.
    + */
    +public class AggregationMapIntermediateUdf<IN extends Tuple, OUT extends Tuple>
extends AggregationUdfBase<OUT> implements MapFunction<IN, OUT>{
    +	private static final long serialVersionUID = 3326127349510588787L;
    +
    +	private AggregationFunction<?, ?>[] functions;
    +	
    +	public AggregationMapIntermediateUdf(AggregationFunction<?, ?>[] functions) {
    +		super(functions.length);
    +		this.functions = functions;
    +	}
    +	
    +	@Override
    +	public OUT map(IN value) throws Exception {
    +		OUT result = createResultTuple();
    --- End diff --
    
    Create the result tuple only once (in the constructor) and reuse it in all map() invocations
to reduce instantiation and GC overhead.


> Add support for out-of-place aggregations
> -----------------------------------------
>
>                 Key: FLINK-1293
>                 URL: https://issues.apache.org/jira/browse/FLINK-1293
>             Project: Flink
>          Issue Type: Improvement
>          Components: Java API, Scala API
>    Affects Versions: 0.7.0-incubating
>            Reporter: Viktor Rosenfeld
>            Assignee: Viktor Rosenfeld
>            Priority: Minor
>
> Currently, the output of an aggregation is of the same type as the input. This restriction
has to major drawbacks:
> 1. Every tuple field can only be used in one aggregation because the aggregations result
is stored in the field.
> 2. Aggregations having a return type that is different from the input type, e.g., count
or average, cannot be implemented.
> It would be nice to have the aggregation return any kind of tuple as a result, so the
restrictions above no longer apply.
> See also:
> - https://github.com/stratosphere/stratosphere/wiki/Design-of-Aggregate-Operator
> - http://apache-flink-incubator-mailing-list-archive.1008284.n3.nabble.com/Hi-Aggregation-support-td2311.html



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