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From rmetzger <...@git.apache.org>
Subject [GitHub] flink pull request: [FLINK-1297] Added OperatorStatsAccumulator fo...
Date Thu, 16 Apr 2015 16:59:07 GMT
Github user rmetzger commented on a diff in the pull request:

    https://github.com/apache/flink/pull/605#discussion_r28528360
  
    --- Diff: flink-core/src/main/java/org/apache/flink/api/common/accumulators/OperatorStatsAccumulator.java
---
    @@ -0,0 +1,98 @@
    +/*
    + * 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.common.accumulators;
    +
    +import org.apache.flink.statistics.OperatorStatistics;
    +import java.io.IOException;
    +import java.io.ObjectInputStream;
    +import java.io.ObjectOutputStream;
    +
    +/**
    + * This accumulator wraps the class {@link org.apache.flink.api.common.accumulators.OperatorStatisticsResult}
to track
    + * estimated values for count distinct and heavy hitters. It has lower memory requirements
than
    + * {@link org.apache.flink.api.common.accumulators.Histogram}.
    + * Our goal in accumulating stats per operator is to not only track global stats, but
also know the local stats of the
    + * subtasks of a task. For this purpose, {@link org.apache.flink.api.common.accumulators.OperatorStatisticsResult}
    + * encapsulates one global accumulator and an array of local accumulators.
    + *
    + * The constructor of the class receives a subTaskIndex, and the total number of subtasks.
    + * Both parameters are found in the
    + * {@link org.apache.flink.api.common.functions.RuntimeContext} from where the constructor
is called.
    + */
    +public class OperatorStatsAccumulator implements Accumulator<Object, OperatorStatisticsResult>
{
    +
    +
    +	private OperatorStatisticsResult localValue;
    +
    +	public OperatorStatsAccumulator(int subTaskIndex, int numSubtasks){
    +		localValue = new OperatorStatisticsResult(subTaskIndex, numSubtasks);
    +	}
    +
    +	@Override
    +	public void add(Object value) {
    +		localValue.add(value);
    +	}
    +
    +	@Override
    +	public OperatorStatisticsResult getLocalValue() {
    +		return localValue;
    +	}
    +
    +	@Override
    +	public void resetLocal() {
    +		localValue.resetLocal();
    +	}
    +
    +	@Override
    +	public void merge(Accumulator<Object, OperatorStatisticsResult> other) {
    +		localValue.merge(other.getLocalValue());
    +	}
    +
    +	//todo this has not been tested
    +	public void write(ObjectOutputStream out) throws IOException {
    +		out.writeObject(localValue.getLocal());
    +
    +	}
    +
    +	//todo this has not been tested
    +	public void read(ObjectInputStream in) throws IOException {
    +		try {
    +			localValue.setLocal((OperatorStatistics) in.readObject());
    +		} catch (ClassNotFoundException e) {
    +			e.printStackTrace();
    --- End diff --
    
    Just doing e.printStackTrace() will make it extremely hard to debug the error. You'll
find a stacktrace without any message in the stderr file ... The flink programm will continue
running in an erroneous state.
    I would recommend re-throwing the exception as a runtime exception.


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