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https://issues.apache.org/jira/browse/BEAM-1573?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15897824#comment-15897824
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Raghu Angadi commented on BEAM-1573:
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New API ({{withKeySerializer() & withValueSerializer()}}) sounds good. We can
mark the old API deprecated and also provide Coder based Kafka Serializer and
Deserializer for if users still want to use the coders (say for transition).
Implementation wise, note that Kafka deserializer would run on Kafka consumer
thread, which is outside normal 'advance()' (invoked by the runner on the
reader). That implies we need to propagate serialization errors appropriately
and throw them in advance(). Alternately we could invoke deserializer
explicitly inside advance() rather than 'consumer poll thread', not sure if
there are any drawbacks to that.
[~peay] PR will be useful.
> KafkaIO does not allow using Kafka serializers and deserializers
> ----------------------------------------------------------------
>
> Key: BEAM-1573
> URL: https://issues.apache.org/jira/browse/BEAM-1573
> Project: Beam
> Issue Type: Improvement
> Components: sdk-java-extensions
> Affects Versions: 0.4.0, 0.5.0
> Reporter: peay
> Assignee: Raghu Angadi
> Priority: Minor
>
> KafkaIO does not allow to override the serializer and deserializer settings
> of the Kafka consumer and producers it uses internally. Instead, it allows to
> set a `Coder`, and has a simple Kafka serializer/deserializer wrapper class
> that calls the coder.
> I appreciate that allowing to use Beam coders is good and consistent with the
> rest of the system. However, is there a reason to completely disallow to use
> custom Kafka serializers instead?
> This is a limitation when working with an Avro schema registry for instance,
> which requires custom serializers. One can write a `Coder` that wraps a
> custom Kafka serializer, but that means two levels of un-necessary wrapping.
> In addition, the `Coder` abstraction is not equivalent to Kafka's
> `Serializer` which gets the topic name as input. Using a `Coder` wrapper
> would require duplicating the output topic setting in the argument to
> `KafkaIO` and when building the wrapper, which is not elegant and error prone.
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