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https://issues.apache.org/jira/browse/FLINK-7210?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16100204#comment-16100204
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ASF GitHub Bot commented on FLINK-7210:
---------------------------------------
Github user aljoscha commented on a diff in the pull request:
https://github.com/apache/flink/pull/4368#discussion_r129339683
--- Diff:
flink-streaming-java/src/main/java/org/apache/flink/streaming/api/functions/sink/TwoPhaseCommitSinkFunction.java
---
@@ -0,0 +1,342 @@
+/*
+ * 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.streaming.api.functions.sink;
+
+import org.apache.flink.annotation.PublicEvolving;
+import org.apache.flink.api.common.state.ListState;
+import org.apache.flink.api.common.state.ListStateDescriptor;
+import org.apache.flink.api.common.typeinfo.TypeHint;
+import org.apache.flink.api.common.typeinfo.TypeInformation;
+import org.apache.flink.configuration.Configuration;
+import org.apache.flink.runtime.state.CheckpointListener;
+import org.apache.flink.runtime.state.FunctionInitializationContext;
+import org.apache.flink.runtime.state.FunctionSnapshotContext;
+import org.apache.flink.streaming.api.checkpoint.CheckpointedFunction;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import javax.annotation.Nullable;
+
+import java.io.Serializable;
+import java.util.ArrayList;
+import java.util.Iterator;
+import java.util.List;
+import java.util.Objects;
+
+import static java.util.Objects.requireNonNull;
+
+/**
+ * This is a recommended base class for all of the {@link SinkFunction}
that intend to implement exactly-once semantic.
+ * It does that by implementing two phase commit algorithm on top of the
{@link CheckpointedFunction} and
+ * {@link CheckpointListener}. User should provide custom TXN (transaction
handle) and implement abstract methods
+ * handling this transaction handle.
+ *
+ * @param <IN> Input type for {@link SinkFunction}
+ * @param <TXN> Transaction to store all of the information required to
handle a transaction (must be Serializable)
+ */
+@PublicEvolving
+public abstract class TwoPhaseCommitSinkFunction<IN, TXN extends
Serializable>
--- End diff --
Why does `TXN` need to be `Serializable`? It should always be serialised
using Flink mechanics (`TypeSerializer` and so on).
> Add TwoPhaseCommitSinkFunction (implementing exactly-once semantic in generic
> way)
> ----------------------------------------------------------------------------------
>
> Key: FLINK-7210
> URL: https://issues.apache.org/jira/browse/FLINK-7210
> Project: Flink
> Issue Type: Improvement
> Components: Streaming Connectors
> Reporter: Piotr Nowojski
> Assignee: Piotr Nowojski
>
> To implement exactly-once sink there is a re-occurring pattern for doing it -
> two phase commit algorithm. It is used both in `BucketingSink` and in
> `Pravega` sink and it will be used in `Kafka 0.11` connector. It would be
> good to extract this common logic into one class, both to improve existing
> implementation (for exampe `Pravega`'s sink doesn't abort interrupted
> transactions) and to make it easier for the users to implement their own
> custom exactly-once sinks.
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