Github user tillrohrmann commented on a diff in the pull request: https://github.com/apache/flink/pull/1620#discussion_r52627131 --- Diff: flink-streaming-java/src/main/java/org/apache/flink/streaming/runtime/operators/GenericExactlyOnceSink.java --- @@ -0,0 +1,173 @@ +/** + * 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 + * <p/> + * http://www.apache.org/licenses/LICENSE-2.0 + * <p/> + * 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.streaming.runtime.operators; + +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.tuple.Tuple; +import org.apache.flink.api.java.typeutils.TypeExtractor; +import org.apache.flink.core.memory.DataInputView; +import org.apache.flink.runtime.state.AbstractStateBackend; +import org.apache.flink.runtime.state.StateHandle; +import org.apache.flink.streaming.api.operators.AbstractStreamOperator; +import org.apache.flink.streaming.api.operators.OneInputStreamOperator; +import org.apache.flink.streaming.api.watermark.Watermark; +import org.apache.flink.streaming.runtime.streamrecord.StreamRecord; +import org.apache.flink.streaming.runtime.tasks.StreamTaskState; + +import java.io.IOException; +import java.io.Serializable; +import java.util.ArrayList; +import java.util.HashMap; +import java.util.HashSet; +import java.util.List; +import java.util.Set; + +/** + * Generic Sink that emits its input elements into an arbitrary backend. This sink is integrated with the checkpointing + * mechanism to provide exactly once semantics. + * + * Incoming records are stored within a {@link org.apache.flink.runtime.state.AbstractStateBackend}, and only committed if a + * checkpoint is completed. Should a job fail while the data is being committed, no exactly once guarantee can be made. + * @param <IN> + */ +public abstract class GenericExactlyOnceSink<IN extends Tuple> extends AbstractStreamOperator<IN> implements OneInputStreamOperator<IN, IN> { + private AbstractStateBackend.CheckpointStateOutputView out; + private TypeSerializer<IN> serializer; + protected TypeInformation<IN> typeInfo; + + private ExactlyOnceState state = new ExactlyOnceState(); + + /** + * Saves a handle in the state. + * @param checkpointId + * @throws IOException + */ + private void saveHandleInState(final long checkpointId) throws IOException { + //only add handle if a new OperatorState was created since the last snapshot/notify + if (out != null) { + out.writeByte(0); //EOF-byte + StateHandle<DataInputView> handle = out.closeAndGetHandle(); + if (state.pendingHandles.containsKey(checkpointId)) { + state.pendingHandles.get(checkpointId).add(handle); + } else { + ArrayList<StateHandle<DataInputView>> list = new ArrayList<>(); + list.add(handle); + state.pendingHandles.put(checkpointId, list); + } + out = null; + } + } + + @Override + public StreamTaskState snapshotOperatorState(final long checkpointId, final long timestamp) throws Exception { + StreamTaskState taskState = super.snapshotOperatorState(checkpointId, timestamp); + saveHandleInState(checkpointId); + taskState.setFunctionState(state); + return taskState; + } + + @Override + public void restoreState(StreamTaskState state, long recoveryTimestamp) throws Exception { + super.restoreState(state, recoveryTimestamp); + this.state = (ExactlyOnceState) state.getFunctionState(); + out = null; + } + + @Override + public void notifyOfCompletedCheckpoint(long checkpointId) throws Exception { + super.notifyOfCompletedCheckpoint(checkpointId); + saveHandleInState(checkpointId); + + synchronized (state.pendingHandles) { + Set<Long> pastCheckpointIds = state.pendingHandles.keySet(); + Set<Long> checkpointsToRemove = new HashSet<>(); + for (Long pastCheckpointId : pastCheckpointIds) { + if (pastCheckpointId <= checkpointId) { + List<StateHandle<DataInputView>> handles = state.pendingHandles.get(pastCheckpointId); + for (StateHandle<DataInputView> handle : handles) { + DataInputView in = handle.getState(getUserCodeClassloader()); + while (in.readByte() == 1) { + IN value = serializer.deserialize(in); + sendValue(value); + } + checkpointsToRemove.add(pastCheckpointId); + } + } + } + for (Long toRemove : checkpointsToRemove) { + state.pendingHandles.remove(toRemove); + } + } + } + + /** + * Write the given element into the backend. + * @param value value to be written + * @throws Exception + */ + protected abstract void sendValue(IN value) throws Exception; + + @Override + public void processElement(StreamRecord<IN> element) throws Exception { + IN value = element.getValue(); + if (serializer == null) { + typeInfo = TypeExtractor.getForObject(value); + serializer = typeInfo.createSerializer(new ExecutionConfig()); + } + //generate initial operator state + if (out == null) { + out = getStateBackend().createCheckpointStateOutputView(0, 0); + } + out.writeByte(1); + serializer.serialize(value, out); + } + + @Override + public void processWatermark(Watermark mark) throws Exception { + //don't do anything, since no are a sink + } + + /** + * This state is used to keep a list of all StateHandles (essentially references to past OperatorStates) that were + * used since the last completed checkpoint. + **/ + public class ExactlyOnceState implements StateHandle<Serializable> { + protected HashMap<Long, ArrayList<StateHandle<DataInputView>>> pendingHandles; + + public ExactlyOnceState() { + pendingHandles = new HashMap<>(); + } + + @Override + public HashMap<Long, ArrayList<StateHandle<DataInputView>>> getState(ClassLoader userCodeClassLoader) throws Exception { + return pendingHandles; + } + + @Override + public void discardState() throws Exception { + pendingHandles = new HashMap<>(); + } + + @Override + public long getStateSize() throws Exception { + return 0; --- End diff -- We should be able to calculate the state as the sum of the state handles stored in `pendingHandles`, shouldn't we?
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