Github user rmetzger commented on a diff in the pull request: https://github.com/apache/flink/pull/1640#discussion_r52994037 --- Diff: flink-streaming-connectors/flink-connector-cassandra/src/main/java/org/apache/flink/streaming/connectors/cassandra/CassandraExactlyOnceSink.java --- @@ -0,0 +1,113 @@ +/** + * 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.connectors.cassandra; + +import com.datastax.driver.core.Cluster; +import com.datastax.driver.core.PreparedStatement; +import com.datastax.driver.core.ResultSet; +import com.datastax.driver.core.ResultSetFuture; +import com.datastax.driver.core.Session; +import com.google.common.util.concurrent.FutureCallback; +import com.google.common.util.concurrent.Futures; +import org.apache.flink.api.java.tuple.Tuple; +import org.apache.flink.streaming.runtime.operators.CheckpointCommitter; +import org.apache.flink.streaming.runtime.operators.GenericExactlyOnceSink; + +/** + * Sink that emits its input elements into a Cassandra database. This sink is integrated with the checkpointing + * mechanism to provide near exactly-once semantics. + * <p/> + * 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> Type of the elements emitted by this sink + */ +public class CassandraExactlyOnceSink<IN extends Tuple> extends GenericExactlyOnceSink<IN> { + private final String host; + private final String createQuery; + private final String insertQuery; + + private transient Cluster cluster; + private transient Session session; + private transient PreparedStatement preparedStatement; + + private transient Throwable exception = null; + + public CassandraExactlyOnceSink(String host, String insertQuery, CheckpointCommitter committer) { + this(host, null, insertQuery, committer); + } + + public CassandraExactlyOnceSink(String host, String createQuery, String insertQuery, CheckpointCommitter committer) { + super(committer); + if (host == null) { + throw new IllegalArgumentException("Host argument must not be null."); + } + if (insertQuery == null) { + throw new IllegalArgumentException("Insert query argument must not be null."); + } + this.host = host; + this.createQuery = createQuery; + this.insertQuery = insertQuery; + } + + @Override + public void close() throws Exception { + super.close(); + session.close(); + cluster.close(); + } + + @Override + public void open() throws Exception { + super.open(); + cluster = Cluster.builder().addContactPoint(host).build(); + session = cluster.connect(); + if (createQuery != null) { + session.execute(createQuery); + } + preparedStatement = session.prepare(insertQuery); + } + + @Override + protected void sendValue(Iterable<IN> values) throws Exception { + //verify that no query failed until now + if (exception != null) { + throw new Exception(exception); --- End diff -- This will leave the cluster and session open.
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