google cloud dataflow - Remove duplicates across window triggers/firings

Question

Let's say I have an unbounded pcollection of sentences keyed by userid, and I want a constantly updated value for whether the user is annoying, we can calculate whether a user is annoying by passing all of the sentences they've ever said into the funcion isAnnoying(). Forever.

I set the window to global with a trigger afterElement(1), accumulatingFiredPanes(), do GroupByKey, then have a ParDo that emits userid,isAnnoying

That works forever, keeps accumulating the state for each user etc. Except it turns out the vast majority of the time a new sentence does not change whether a user isAnnoying, and so most of the times the window fires and emits a userid,isAnnoying tuple it's a redundant update and the io was unnecessary. How do I catch these duplicate updates and drop while still getting an update every time a sentence comes in that does change the isAnnoying value?

Answer 1

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