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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