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[streaming] Fast calculation of medians of windows
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124 changes: 124 additions & 0 deletions
124
...n/java/org/apache/flink/streaming/api/windowing/windowbuffer/MedianGroupedPreReducer.java
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| /* | ||
| * 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. | ||
| */ | ||
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| package org.apache.flink.streaming.api.windowing.windowbuffer; | ||
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| import org.apache.flink.api.common.ExecutionConfig; | ||
| import org.apache.flink.api.common.typeinfo.TypeInformation; | ||
| import org.apache.flink.api.common.typeutils.TypeSerializer; | ||
| import org.apache.flink.api.java.functions.KeySelector; | ||
| import org.apache.flink.streaming.api.windowing.StreamWindow; | ||
| import org.apache.flink.streaming.util.FieldAccessor; | ||
| import org.apache.flink.util.Collector; | ||
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| import java.io.Serializable; | ||
| import java.util.Map; | ||
| import java.util.TreeMap; | ||
| import java.util.Queue; | ||
| import java.util.ArrayDeque; | ||
| import java.util.Iterator; | ||
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| /** | ||
| * Grouped pre-reducer for calculating median with any eviction policy. | ||
| * | ||
| * It stores a MedianPreReducer for every group. | ||
| */ | ||
| public class MedianGroupedPreReducer<T> extends WindowBuffer<T> implements PreAggregator, Serializable { | ||
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| private static final long serialVersionUID = 1L; | ||
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| // This is for getting and setting the field specified in the parameters to the median call. | ||
| private FieldAccessor<T, Double> fieldAccessor; | ||
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| private TypeSerializer<T> serializer; | ||
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| private KeySelector<T, ?> keySelector; | ||
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| // PreReducers for the individual groups | ||
| private Map<Object, MedianPreReducer<T>> groupPreReducers = new TreeMap<Object, MedianPreReducer<T>>(); | ||
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| // Holds a reference for the groupPreReducer belonging to each element currently in the window. | ||
| // (This is used at evict, so that we have to index into groupPreReducers only on store.) | ||
| private Queue<MedianPreReducer<T>> groupPreReducerPerElement = new ArrayDeque<MedianPreReducer<T>>(); | ||
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| public MedianGroupedPreReducer(FieldAccessor<T, Double> fieldAccessor, TypeSerializer<T> serializer, | ||
| KeySelector<T, ?> keySelector) { | ||
| this.fieldAccessor = fieldAccessor; | ||
| this.serializer = serializer; | ||
| this.keySelector = keySelector; | ||
| } | ||
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| public MedianGroupedPreReducer(int pos, TypeInformation<T> typeInfo, ExecutionConfig config, | ||
| KeySelector<T, ?> keySelector) { | ||
| this.fieldAccessor = FieldAccessor.create(pos, typeInfo, config); | ||
| this.serializer = typeInfo.createSerializer(config); | ||
| this.keySelector = keySelector; | ||
| } | ||
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| public MedianGroupedPreReducer(String field, TypeInformation<T> typeInfo, ExecutionConfig config, | ||
| KeySelector<T, ?> keySelector) { | ||
| this.fieldAccessor = FieldAccessor.create(field, typeInfo, config); | ||
| this.serializer = typeInfo.createSerializer(config); | ||
| this.keySelector = keySelector; | ||
| } | ||
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| @Override | ||
| public void store(T elem) throws Exception { | ||
| Object key = keySelector.getKey(elem); | ||
| MedianPreReducer<T> groupPreReducer = groupPreReducers.get(key); | ||
| if(groupPreReducer == null) { // Group doesn't exist yet, create it. | ||
| groupPreReducer = new MedianPreReducer<T>(fieldAccessor, serializer); | ||
| groupPreReducers.put(key, groupPreReducer); | ||
| } | ||
| groupPreReducer.store(elem); | ||
| groupPreReducerPerElement.add(groupPreReducer); | ||
| } | ||
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| @Override | ||
| public void evict(int n) { | ||
| for (int i = 0; i < n; i++) { | ||
| MedianPreReducer<T> groupPreReducer = groupPreReducerPerElement.poll(); | ||
| if(groupPreReducer == null) { | ||
| break; | ||
| } | ||
| groupPreReducer.evict(1); | ||
| } | ||
| } | ||
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| @Override | ||
| public void emitWindow(Collector<StreamWindow<T>> collector) { | ||
| StreamWindow<T> currentWindow = createEmptyWindow(); | ||
| for(Iterator<MedianPreReducer<T>> it = groupPreReducers.values().iterator(); it.hasNext(); ) { | ||
| MedianPreReducer<T> groupPreReducer = it.next(); | ||
| T groupMedian = groupPreReducer.getMedian(); | ||
| if(groupMedian != null) { | ||
| currentWindow.add(groupMedian); | ||
| } else { | ||
| it.remove(); // Remove groups that don't contain elements, to not leak memory for long ago seen groups. | ||
| } | ||
| } | ||
| if(!currentWindow.isEmpty() || emitEmpty) { | ||
| collector.collect(currentWindow); | ||
| } | ||
| } | ||
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| @Override | ||
| public WindowBuffer<T> clone() { | ||
| return new MedianGroupedPreReducer<T>(fieldAccessor, serializer, keySelector); | ||
| } | ||
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| } |
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