westphal-jan commented on a change in pull request #15140: URL: https://github.com/apache/flink/pull/15140#discussion_r594983899
########## File path: flink-connectors/flink-connector-rabbitmq2/src/main/java/org/apache/flink/connector/rabbitmq2/sink/writer/specalized/RabbitMQSinkWriterExactlyOnce.java ########## @@ -0,0 +1,135 @@ +/* + * 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.connector.rabbitmq2.sink.writer.specalized; + +import org.apache.flink.api.common.serialization.SerializationSchema; +import org.apache.flink.api.connector.sink.SinkWriter; +import org.apache.flink.connector.rabbitmq2.RabbitMQConnectionConfig; +import org.apache.flink.connector.rabbitmq2.sink.RabbitMQSink; +import org.apache.flink.connector.rabbitmq2.sink.RabbitMQSinkPublishOptions; +import org.apache.flink.connector.rabbitmq2.sink.SerializableReturnListener; +import org.apache.flink.connector.rabbitmq2.sink.SinkMessage; +import org.apache.flink.connector.rabbitmq2.sink.state.RabbitMQSinkWriterState; +import org.apache.flink.connector.rabbitmq2.sink.writer.RabbitMQSinkWriterBase; + +import com.rabbitmq.client.Channel; +import com.rabbitmq.client.Connection; + +import java.io.IOException; +import java.util.ArrayList; +import java.util.Collections; +import java.util.List; + +/** + * A {@link SinkWriter} implementation for {@link RabbitMQSink} that provides exactly-once delivery + * guarantees, which means incoming stream elements will be delivered to RabbitMQ exactly once. For + * this, checkpointing needs to be enabled. + * + * <p>Exactly-once behaviour is implemented using a transactional RabbitMQ channel. All incoming + * stream elements are buffered in the state of this writer until the next checkpoint is triggered. + * All buffered {@code messages} are then send to RabbitMQ in a single transaction. When successful, + * all messages committed get removed from the state. If the transaction is aborted, all messages + * are put back into the state and send on the next checkpoint. + * + * <p>The transactional channel is heavyweight and will decrease throughput. If the system is under + * heavy load, consecutive checkpoints can be delayed if commits take longer than the checkpointing + * interval specified. Only use exactly-once if necessary (no duplicated messages in RabbitMQ + * allowed), otherwise consider using at-least-once. + * + * @param <T> Type of the elements in this sink + */ +public class RabbitMQSinkWriterExactlyOnce<T> extends RabbitMQSinkWriterBase<T> { + + /** All messages that arrived and could not be committed this far. */ + private List<SinkMessage<T>> messages; + + /** + * Create a new RabbitMQSinkWriterExactlyOnce. + * + * @param connectionConfig configuration parameters used to connect to RabbitMQ + * @param queueName name of the queue to publish to + * @param serializationSchema serialization schema to turn elements into byte representation + * @param publishOptions optionally used to compute routing/exchange for messages + * @param maxRetry number of retries for each message + * @param returnListener return listener + * @param states a list of states to initialize this reader with + */ + public RabbitMQSinkWriterExactlyOnce( + RabbitMQConnectionConfig connectionConfig, + String queueName, + SerializationSchema<T> serializationSchema, + RabbitMQSinkPublishOptions<T> publishOptions, + int maxRetry, + SerializableReturnListener returnListener, + List<RabbitMQSinkWriterState<T>> states) { + super( + connectionConfig, + queueName, + serializationSchema, + publishOptions, + maxRetry, + returnListener); + messages = new ArrayList<>(); + initWithState(states); + } + + private void initWithState(List<RabbitMQSinkWriterState<T>> states) { + List<SinkMessage<T>> messages = new ArrayList<>(); + for (RabbitMQSinkWriterState<T> state : states) { + messages.addAll(state.getOutstandingMessages()); + } + this.messages = messages; + } + + protected Channel setupChannel(Connection rmqConnection) throws IOException { + Channel rmqChannel = super.setupChannel(rmqConnection); + // puts channel in commit mode + rmqChannel.txSelect(); + return rmqChannel; + } + + @Override + public void write(T element, Context context) { + messages.add(new SinkMessage<>(element, serializationSchema.serialize(element))); + } + + @Override + public List<RabbitMQSinkWriterState<T>> snapshotState() { + commitMessages(); + return Collections.singletonList(new RabbitMQSinkWriterState<>(messages)); + } + + private void commitMessages() { + List<SinkMessage<T>> messagesToSend = new ArrayList<>(messages); + messages.subList(0, messagesToSend.size()).clear(); + try { + for (SinkMessage<T> msg : messagesToSend) { + super.send(msg); + } + rmqChannel.txCommit(); + LOG.info("Successfully committed {} messages.", messagesToSend.size()); + } catch (IOException e) { + LOG.error( Review comment: In the new architecture we commit a list of committables and return those that failed to the system. ---------------------------------------------------------------- This is an automated message from the Apache Git Service. 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