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https://issues.apache.org/jira/browse/FLINK-3332?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15148370#comment-15148370
]
ASF GitHub Bot commented on FLINK-3332:
---------------------------------------
Github user tillrohrmann commented on a diff in the pull request:
https://github.com/apache/flink/pull/1640#discussion_r52988789
--- Diff:
flink-streaming-java/src/main/java/org/apache/flink/streaming/runtime/operators/GenericExactlyOnceSink.java
---
@@ -0,0 +1,195 @@
+/**
+ * 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.typeinfo.TypeInformation;
+import org.apache.flink.api.common.typeutils.TypeSerializer;
+import org.apache.flink.api.java.typeutils.TypeExtractor;
+import org.apache.flink.core.memory.DataInputView;
+import org.apache.flink.runtime.io.disk.InputViewIterator;
+import org.apache.flink.runtime.state.AbstractStateBackend;
+import org.apache.flink.runtime.state.StateHandle;
+import
org.apache.flink.runtime.util.NonReusingMutableToRegularIteratorWrapper;
+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.HashSet;
+import java.util.Set;
+import java.util.TreeMap;
+import java.util.UUID;
+
+/**
+ * Generic Sink that emits its input elements into an arbitrary backend.
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 abstract class GenericExactlyOnceSink<IN> extends
AbstractStreamOperator<IN> implements OneInputStreamOperator<IN, IN> {
+ private transient AbstractStateBackend.CheckpointStateOutputView out;
+ private TypeSerializer<IN> serializer;
+ protected transient TypeInformation<IN> typeInfo;
+ protected final CheckpointCommitter committer;
+ protected final String id;
+
+ private ExactlyOnceState state = new ExactlyOnceState();
+
+ public GenericExactlyOnceSink(CheckpointCommitter committer) {
+ if (committer == null) {
+ throw new IllegalArgumentException("CheckpointCommitter
argument must not be null.");
+ }
+ this.committer = committer;
+ this.id = UUID.randomUUID().toString();
+ }
+
+ @Override
+ public void open() throws Exception {
+ committer.setOperatorId(id);
+
committer.setOperatorSubtaskId(getRuntimeContext().getIndexOfThisSubtask());
+ committer.open();
+ }
+
+ public void close() throws Exception {
+ committer.close();
+ }
+
+ /**
+ * 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
+ if (out != null) {
+ StateHandle<DataInputView> handle =
out.closeAndGetHandle();
+ state.pendingHandles.put(checkpointId, handle);
+ 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);
+
+ synchronized (state.pendingHandles) {
+ Set<Long> pastCheckpointIds =
state.pendingHandles.keySet();
+ Set<Long> checkpointsToRemove = new HashSet<>();
+ for (Long pastCheckpointId : pastCheckpointIds) {
+ if (pastCheckpointId <= checkpointId) {
+ if
(!committer.isCheckpointCommitted(pastCheckpointId)) {
+ StateHandle<DataInputView>
handle = state.pendingHandles.get(pastCheckpointId);
+ DataInputView in =
handle.getState(getUserCodeClassloader());
+ sendValue(new
NonReusingMutableToRegularIteratorWrapper<>(new InputViewIterator<>(in,
serializer), serializer));
+
committer.commitCheckpoint(pastCheckpointId);
+ }
+
checkpointsToRemove.add(pastCheckpointId);
+ }
+ }
+ for (Long toRemove : checkpointsToRemove) {
+ StateHandle<DataInputView> handle =
state.pendingHandles.get(toRemove);
+ state.pendingHandles.remove(toRemove);
+ handle.discardState();
+ }
+ }
+ }
+
+
+ /**
+ * Write the given element into the backend.
+ *
+ * @param value value to be written
+ * @throws Exception
+ */
+ protected abstract void sendValue(Iterable<IN> value) throws Exception;
+
+ @Override
+ public void processElement(StreamRecord<IN> element) throws Exception {
+ IN value = element.getValue();
+ if (serializer == null) {
+ typeInfo = TypeExtractor.getForObject(value);
--- End diff --
This won't work here. Assume that you have a stream of some super class
`S`. The first element you see is a sub class `A` so you will instantiate a
serializer of this type. But when you see next another sub class `B`, then it
will fail.
I think you should pass the serializer to the operator when it is
instantiated on the client side.
> Provide an exactly-once Cassandra connector
> -------------------------------------------
>
> Key: FLINK-3332
> URL: https://issues.apache.org/jira/browse/FLINK-3332
> Project: Flink
> Issue Type: Improvement
> Components: Streaming Connectors
> Reporter: Robert Metzger
> Assignee: Chesnay Schepler
>
> With FLINK-3311, we are adding a Cassandra connector to Flink.
> It would be good to also provide an "exactly-once" C* connector.
> I would like to first discuss how we are going to implement this in Flink.
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