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  • KIP-328: Ability to suppress updates for KTables

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Windowed computations in particular present a unique opportunity. The output of a windowed computation is a KTable in which the keys are annotated with window ids. Because the window has a defined end, we know that the keys belonging to that window can never be modified again once that end time has passed, except by lateout-of-arriving order events. If we bound the lateness "maximum allowed delay" of events, we can know the "final value" of the window. This is especially useful for taking irrevocable actions in response to window results, such as sending an email or alert when a windowed aggregation is below a certain threshold.