[jira] [Resolved] (KAFKA-7079) ValueTransformerWithKeySupplier is not mentioned in the documentation

["Matthias J. Sax (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/KAFKA-7079?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Matthias J. Sax resolved KAFKA-7079.
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    Resolution: Won't Fix

> ValueTransformerWithKeySupplier is not mentioned in the documentation
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>                 Key: KAFKA-7079
>                 URL: https://issues.apache.org/jira/browse/KAFKA-7079
>             Project: Kafka
>          Issue Type: Bug
>          Components: streams
>    Affects Versions: 1.1.0
>         Environment: Fedora 27
>            Reporter: Hashan Gayasri Udugahapattuwa
>            Priority: Major
>
> ValueTransformer#transform does not pass the key
> KStream#transformValues(ValueTransformerWithKeySupplier ..... method is not documented. It might lead to people to use workarounds or fall back to using Transformer. This is very likely if the user is using a wrapper API (i.e: for Scala) as the user would be checking the documentation more than the available API functions in code.
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> *Original issue (as it might be useful as a business requirement)*
> ValueTransformers' transform method doesn't pass the key to user-code. Reporting this as a bug since it currently requires workarounds.
> Context:
> I'm currently in the process of converting two stateful "*aggregate*" DSL operations to the Processor API since the state of those operations are relatively large and takes 99% + of CPU time (when profiled) for serializing and deserializing them via Kryo. 
> Since DSL aggregations use state stores of [Bytes, Array[Byte]]] even when using the in-memory state store, it seems like the only way to reduce the serialization/deserialization overhead is to convert heavy aggregates to *transform*s.
> In my case, *ValueTransformer* seems to be the option. However, since ValueTransformers' _transform_ method only exposes the _value_, I'd either have to pre-process and add the key to the value or use *Transformer* instead (which is not my intent).
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> As internal _*InternalValueTransformerWithKey*_ already has the readOnlyKey, it seems like a good idea to pass the key to the transform method as well, esp since in a stateful transformation, generally the state store has to be queried by the key.



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