Github user zentol commented on a diff in the pull request:
https://github.com/apache/flink/pull/1771#discussion_r63678427
--- Diff:
flink-streaming-java/src/main/java/org/apache/flink/streaming/runtime/operators/GenericAtLeastOnceSink.java
---
@@ -0,0 +1,192 @@
+/**
+ * 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.typeutils.TypeSerializer;
+import org.apache.flink.api.java.tuple.Tuple2;
+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.ReusingMutableToRegularIteratorWrapper;
+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 org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+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 and can provide exactly-once guarantees; depending on the
storage backend and sink/committer implementation.
+ * <p/>
+ * Incoming records are stored within a {@link
org.apache.flink.runtime.state.AbstractStateBackend}, and only committed if a
+ * checkpoint is completed.
+ *
+ * @param <IN> Type of the elements emitted by this sink
+ */
+public abstract class GenericAtLeastOnceSink<IN> extends
AbstractStreamOperator<IN> implements OneInputStreamOperator<IN, IN> {
+ protected static final Logger LOG =
LoggerFactory.getLogger(GenericAtLeastOnceSink.class);
+ private final CheckpointCommitter committer;
+ private transient AbstractStateBackend.CheckpointStateOutputView out;
+ protected final TypeSerializer<IN> serializer;
+ private final String id;
+
+ private ExactlyOnceState state = new ExactlyOnceState();
+
+ public GenericAtLeastOnceSink(CheckpointCommitter committer,
TypeSerializer<IN> serializer, String jobID) throws Exception {
+ this.committer = committer;
+ this.serializer = serializer;
+ this.id = UUID.randomUUID().toString();
+ this.committer.setJobId(jobID);
+ this.committer.createResource();
+ }
+
+ @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, final long
timestamp) throws Exception {
+ //only add handle if a new OperatorState was created since the
last snapshot
+ if (out != null) {
+ StateHandle<DataInputView> handle =
out.closeAndGetHandle();
+ if (state.pendingHandles.containsKey(checkpointId)) {
+ //we already have a checkpoint stored for that
ID that may have been partially written,
+ //so we discard this "alternate version" and
use the stored checkpoint
+ handle.discardState();
+ } else {
+ state.pendingHandles.put(checkpointId, new
Tuple2<>(timestamp, handle));
+ }
+ out = null;
+ }
+ }
+
+ @Override
+ public StreamTaskState snapshotOperatorState(final long checkpointId,
final long timestamp) throws Exception {
+ StreamTaskState taskState =
super.snapshotOperatorState(checkpointId, timestamp);
+ saveHandleInState(checkpointId, timestamp);
+ 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)) {
--- End diff --
whether it triggers a lookup is up to the Committer implementation. You
could always keep a local version, and only lookup the value when the local
version is null.
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