boyuanzz commented on a change in pull request #11715: URL: https://github.com/apache/beam/pull/11715#discussion_r425995961
########## File path: sdks/java/core/src/main/java/org/apache/beam/sdk/transforms/splittabledofn/GrowableOffsetRangeTracker.java ########## @@ -0,0 +1,103 @@ +/* + * 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.transforms.splittabledofn; + +import static org.apache.beam.vendor.guava.v26_0_jre.com.google.common.base.Preconditions.checkNotNull; + +import org.apache.beam.sdk.annotations.Experimental; +import org.apache.beam.sdk.annotations.Experimental.Kind; +import org.apache.beam.sdk.io.range.OffsetRange; + +/** + * A special {@link OffsetRangeTracker} for tracking a growable offset range. The Long.MAX_VALUE is + * used as end range to indicate the possibility of infinity. + * + * <p>A offset range is considered as growable when the end offset could grow(or change) during + * execution time(e.g., Kafka backlog, appended file). + */ +@Experimental(Kind.SPLITTABLE_DO_FN) +public class GrowableOffsetRangeTracker extends OffsetRangeTracker { + /** + * An interface that should be implemented to fetch estimated end offset of range. + * + * <p>{@code estimateRangeEnd} is called to give te end offset when {@code trySplit} or {@code + * getProgress} is invoked. The end offset is exclusive for the range. It's not necessary to + * increase monotonically but it's only taken into computation when it's larger than the current + * position. When returning Long.MAX_VALUE as estimate, it means the largest possible position for + * the range is Long.MAX_VALUE - 1. Having a good estimate is important for providing a good + * signal of progress and splitting at a proper position. + */ + public interface OffsetPoller { + long estimateRangeEnd(); + } + + private final OffsetPoller poller; + + public GrowableOffsetRangeTracker(long start, OffsetPoller offsetPoller) { + super(new OffsetRange(start, Long.MAX_VALUE)); + this.poller = checkNotNull(offsetPoller); + } + + @Override + public SplitResult<OffsetRange> trySplit(double fractionOfRemainder) { + // If current tracking range is no longer growable, split it as a normal range. + if (range.getTo() != Long.MAX_VALUE || range.getTo() == range.getFrom()) { + return super.trySplit(fractionOfRemainder); + } + long cur = (lastAttemptedOffset == null) ? range.getFrom() - 1 : lastAttemptedOffset; + + // If current range has been done, there is no more space to split. + if (cur == Long.MAX_VALUE) { + return null; + } + // Fetch the estimated end offset. If the estimated end is smaller than the next offset, use + // the next offset as end. + long estimateLatestOffset = Long.max(poller.estimateRangeEnd(), cur + 1); + long splitPos = + cur + + Math.max( + 1L, + (Double.valueOf((estimateLatestOffset - cur) * fractionOfRemainder)).longValue()); + + if (splitPos > estimateLatestOffset) { + return null; + } + OffsetRange res = new OffsetRange(splitPos, range.getTo()); + this.range = new OffsetRange(range.getFrom(), splitPos); + return SplitResult.of(range, res); Review comment: btw we will also loss `lastAttemptedOffset` by creating a new tracker. ---------------------------------------------------------------- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. For queries about this service, please contact Infrastructure at: [email protected]
