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To breakdown, the TopN operator is aiming at globally sort all the emitted key-value pairs from upstream operator, and only retain the top N values within its state as a KTable. We also see cases where the TopN query is partitioned, such as a salesperson wants to know the best sellers in different categories.      Considering the nature of ever updating streams, it is also necessary to support windowed TopN as well.

Compatibility, Deprecation, and Migration Plan

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