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The second option quite obviously is the recommended one. While it is uncertain if we will need to give the user the ability to choose between these two options, it would probably be necessary. In the latter option, it should be emphasized that the hash function must be chosen carefully. In many cases, Kafka already loads the prior result anyway. So for instances where we already load the previous result, we will just use that instead of the hash code (if we are to implement option 2). 

Discourse on other areas

The timestamps of the results processed would also present a serious design challenge for this KIP. The requirements of emit on change would entail the following behavior:

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