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Please keep the discussion on the mailing list rather than commenting on the wiki (wiki discussions get unwieldy fast).

Motivation

Describe the problems you are trying to solveCurrently in the Stream-Stream window joining context, the joiner will take in two incoming data streams, for example A and B. Upon new record arrival from A/B,  joiner will apply exhaustive search on window store B/A to get the all the possible joining records. However, the joiner could not optimize the case where we only care about exactly one match, or say the first seen. We are proposing a new API which could enforce a joining called "FirstOrderJoin" which only returns the first seen key-value pair on the other side.

Public Interfaces

Briefly list any new interfaces that will be introduced as part of this proposal or any existing interfaces that will be removed or changed. The purpose of this section is to concisely call out the public contract that will come along with this feature.

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