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https://issues.apache.org/jira/browse/KAFKA-4691?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15838245#comment-15838245
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Matthias J. Sax commented on KAFKA-4691:
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I am not sure, if we can fix this soon. The problem is, that Streams uses a
single `KafkaProducer` for all output topics. All those output topics might
have different types for keys and values while `KafkaProducer` can only be
configures to use a single serializer; one for the key and one for the value.
Thus, Kafka Streams configures the producer to use {{byte[]}} as key and value
type and use the appropriate serializers per output topic before handing the
record to the producer. Right now, I would rather close this as "won't fix".
\cc [~guozhang]
> ProducerInterceptor.onSend() is called after key and value are serialized
> -------------------------------------------------------------------------
>
> Key: KAFKA-4691
> URL: https://issues.apache.org/jira/browse/KAFKA-4691
> Project: Kafka
> Issue Type: Bug
> Components: clients, streams
> Affects Versions: 0.10.1.1
> Reporter: Francesco Lemma
> Labels: easyfix
> Attachments: 2017-01-24 00_50_55-SDG_CR33_DevStudio - Java EE -
> org.apache.kafka.streams.processor.internals.Reco.png
>
>
> According to the JavaDoc
> (https://kafka.apache.org/0101/javadoc/org/apache/kafka/clients/producer/ProducerInterceptor.html)
> " This is called from KafkaProducer.send(ProducerRecord) and
> KafkaProducer.send(ProducerRecord, Callback) methods, before key and value
> get serialized and partition is assigned (if partition is not specified in
> ProducerRecord)".
> Although when using this with Kafka Streams
> (StreamsConfig.producerPrefix(ProducerConfig.INTERCEPTOR_CLASSES_CONFIG)) the
> key and value contained in the record object are already serialized.
> As you can see from the screenshot, the serialization is performed inside
> RecordCollectionImpl.send(ProducerRecord<K, V> record, Serializer<K>
> keySerializer, Serializer<V> valueSerializer,
> StreamPartitioner<K, V> partitioner), effectively
> before calling the send method of the producer which will trigger the
> interceptor.
> This makes it unable to perform any kind of operation involving the key or
> value of the message, unless at least performing an additional
> deserialization.
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