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https://issues.apache.org/jira/browse/FLINK-3679?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15882267#comment-15882267
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ASF GitHub Bot commented on FLINK-3679:
---------------------------------------
Github user tzulitai commented on a diff in the pull request:
https://github.com/apache/flink/pull/3314#discussion_r102900064
--- Diff:
flink-connectors/flink-connector-kafka-base/src/main/java/org/apache/flink/streaming/util/serialization/RichKeyedDeserializationSchema.java
---
@@ -0,0 +1,54 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
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+ * 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
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+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
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+ * distributed under the License is distributed on an "AS IS" BASIS,
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+ */
+package org.apache.flink.streaming.util.serialization;
--- End diff --
Since this is now a very Kafka-specific class, I think this is good timing
to change to the package path `org.apache.flink.streaming.kafka.serialization`
now.
The original `KeyedDeserializationSchema` was placed under
`o.a.f.s.util.serialization` because it was wrongly packaged in another module
before, and moved to `flink-connector-kafka-base` under the same package path
to avoid breaking user code.
> DeserializationSchema should handle zero or more outputs for every input
> ------------------------------------------------------------------------
>
> Key: FLINK-3679
> URL: https://issues.apache.org/jira/browse/FLINK-3679
> Project: Flink
> Issue Type: Bug
> Components: DataStream API, Kafka Connector
> Reporter: Jamie Grier
> Assignee: Haohui Mai
>
> There are a couple of issues with the DeserializationSchema API that I think
> should be improved. This request has come to me via an existing Flink user.
> The main issue is simply that the API assumes that there is a one-to-one
> mapping between input and outputs. In reality there are scenarios where one
> input message (say from Kafka) might actually map to zero or more logical
> elements in the pipeline.
> Particularly important here is the case where you receive a message from a
> source (such as Kafka) and say the raw bytes don't deserialize properly.
> Right now the only recourse is to throw IOException and therefore fail the
> job.
> This is definitely not good since bad data is a reality and failing the job
> is not the right option. If the job fails we'll just end up replaying the
> bad data and the whole thing will start again.
> Instead in this case it would be best if the user could just return the empty
> set.
> The other case is where one input message should logically be multiple output
> messages. This case is probably less important since there are other ways to
> do this but in general it might be good to make the
> DeserializationSchema.deserialize() method return a collection rather than a
> single element.
> Maybe we need to support a DeserializationSchema variant that has semantics
> more like that of FlatMap.
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