[FLINK-17074] Deprecate DataStream.keyBy() that use tuple/expression keys

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Done
• Fix Version/s: 1.11.0
• Component/s: API / DataStream, API / Scala
• Labels: pull-request-available starter
• Assignee: Etienne Chauchot
• Reporter: Aljoscha Krettek
• Created: 09/Apr/20 15:27
• Updated: 13/Jan/21 23:00
• Resolved: 28/Apr/20 07:57

Description

Currently you can either specify a KeySelector, tuple positions, and expression keys? I think KeySelectors are strictly superior and with lambdas (or function references) quite easy to use. Tuple/expression keys use reflection underneath to do the field accesses, so performance is strictly worse. Also, when using a KeySelector you will have a meaningful key type KEY in your operations while for tuple/expression keys the key type is simply Tuple.

Tuple/expression keys were introduced before Java got support for lambdas in Java 8 and before we added the Table API. Nowadays, using a lambda is little more typing than using an expression key but is (possibly) faster and more type safe. The Table API should be used for these more expression-based/relational use cases.

Issue Links

• links to: GitHub Pull Request #11886