Page History

...

'Distinct' operation is common in data processing, e. g.

• SQL DISTINCT keyword,
• In standard libraries for programming languages
  • .NET LINQ Distinct method,
  • Java
  java.util.stream.
  • Stream distinct()
  method
  • ,
  .NET LINQ Distinct method,
  • Scala Seq distinct(),
• In data processing frameworks:

  • Apache Spark's distinct(),

  • Apache Flink's distinct(),
  • Apache Beam's Distinct(),
  • Hazelcast Jet's distinct(), etc.

Hence it is natural to expect the similar functionality from Kafka Streams.

Although Kafka Streams Tutorials contains an example of how distinct can be emulated, but this example is complicated: it involves low-level coding with local state store and a custom transformer. It might be much more convenient to have distinct as a first-class DSL operation.

Due to 'infinite' nature of KStream, distinct operation should be windowed, similar to windowed joins and aggregations for KStreams.

...