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https://issues.apache.org/jira/browse/FLINK-3679?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15882264#comment-15882264
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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_r102896783
--- Diff:
flink-connectors/flink-connector-kafka-0.8/src/main/java/org/apache/flink/streaming/connectors/kafka/FlinkKafkaConsumer08.java
---
@@ -176,7 +177,7 @@ public FlinkKafkaConsumer08(List<String> topics,
DeserializationSchema<T> deseri
* @param props
* The properties that are used to configure both the fetcher
and the offset handler.
*/
- public FlinkKafkaConsumer08(List<String> topics,
KeyedDeserializationSchema<T> deserializer, Properties props) {
+ public FlinkKafkaConsumer08(List<String> topics,
RichKeyedDeserializationSchema<T> deserializer, Properties props) {
--- End diff --
This will break user-code. We'll need proper usage migration here.
We have a separate JIRA that aims at deprecating the current Kafka Consumer
constructors: https://issues.apache.org/jira/browse/FLINK-5704. The migration
to use the new flat-map deserialzer can be included there.
Perhaps for this PR, we should just use your
`RichKeyedDeserializationSchemaWrapper` as "behaviour bridges" for the original
deserialization schema to the new one, and don't change the original
constructor / include new constructors yet, so that we don't overlap and
complicate things for FLINK-5704.
> 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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