org.apache.beam.sdk.util.Reshuffle.java Source code

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Here is the source code for org.apache.beam.sdk.util.Reshuffle.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.
 */
package org.apache.beam.sdk.util;

import org.apache.beam.sdk.transforms.DoFn;
import org.apache.beam.sdk.transforms.GroupByKey;
import org.apache.beam.sdk.transforms.PTransform;
import org.apache.beam.sdk.transforms.ParDo;
import org.apache.beam.sdk.transforms.windowing.BoundedWindow;
import org.apache.beam.sdk.transforms.windowing.OutputTimeFns;
import org.apache.beam.sdk.transforms.windowing.Window;
import org.apache.beam.sdk.values.KV;
import org.apache.beam.sdk.values.PCollection;
import org.apache.beam.sdk.values.TimestampedValue;
import org.joda.time.Duration;

/**
 * A {@link PTransform} that returns a {@link PCollection} equivalent to its input but operationally
 * provides some of the side effects of a {@link GroupByKey}, in particular preventing fusion of
 * the surrounding transforms, checkpointing and deduplication by id (see
 * {@link ValueWithRecordId}).
 *
 * <p>Performs a {@link GroupByKey} so that the data is key-partitioned. Configures the
 * {@link WindowingStrategy} so that no data is dropped, but doesn't affect the need for
 * the user to specify allowed lateness and accumulation mode before a user-inserted GroupByKey.
 *
 * @param <K> The type of key being reshuffled on.
 * @param <V> The type of value being reshuffled.
 */
public class Reshuffle<K, V> extends PTransform<PCollection<KV<K, V>>, PCollection<KV<K, V>>> {

    private Reshuffle() {
    }

    public static <K, V> Reshuffle<K, V> of() {
        return new Reshuffle<K, V>();
    }

    @Override
    public PCollection<KV<K, V>> expand(PCollection<KV<K, V>> input) {
        WindowingStrategy<?, ?> originalStrategy = input.getWindowingStrategy();
        // If the input has already had its windows merged, then the GBK that performed the merge
        // will have set originalStrategy.getWindowFn() to InvalidWindows, causing the GBK contained
        // here to fail. Instead, we install a valid WindowFn that leaves all windows unchanged.
        // The OutputTimeFn is set to ensure the GroupByKey does not shift elements forwards in time.
        // Because this outputs as fast as possible, this should not hold the watermark.
        Window<KV<K, V>> rewindow = Window
                .<KV<K, V>>into(new IdentityWindowFn<>(originalStrategy.getWindowFn().windowCoder()))
                .triggering(new ReshuffleTrigger<>()).discardingFiredPanes()
                .withOutputTimeFn(OutputTimeFns.outputAtEarliestInputTimestamp())
                .withAllowedLateness(Duration.millis(BoundedWindow.TIMESTAMP_MAX_VALUE.getMillis()));

        return input.apply(rewindow).apply("ReifyOriginalTimestamps", ReifyTimestamps.<K, V>inValues())
                .apply(GroupByKey.<K, TimestampedValue<V>>create())
                // Set the windowing strategy directly, so that it doesn't get counted as the user having
                // set allowed lateness.
                .setWindowingStrategyInternal(originalStrategy).apply("ExpandIterable",
                        ParDo.of(new DoFn<KV<K, Iterable<TimestampedValue<V>>>, KV<K, TimestampedValue<V>>>() {
                            @ProcessElement
                            public void processElement(ProcessContext c) {
                                K key = c.element().getKey();
                                for (TimestampedValue<V> value : c.element().getValue()) {
                                    c.output(KV.of(key, value));
                                }
                            }
                        }))
                .apply("RestoreOriginalTimestamps", ReifyTimestamps.<K, V>extractFromValues());
    }
}