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In this FLIP, we propose to optimize performance for the above use-cases by allowing an operator to effectively switch its execution mode from batch to stream based on the "backlog" status of the records emitted by the source operators.

NOTE: This FLIP focuses only on the capability to switch from batch to stream mode. If there is any extra API needed to support switching from stream to batch mode, we will discuss them in a follow-up FLIP.

Behavior changes when switching from batch mode to stream mode

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