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1. The polling thread send a commit event.  The commit event has a completable future.
2. Wait for the completable future to finish, so that we can make this a blocking API

Assign

1. If we are assigning nothing, trigger unsubscribe()
2. clear the fetcher buffer
3. send a commit event if autocommit is enabled
4. send metadata update

Subscribe

1. If subscribing to nothing, trigger unsubscribe()
2. clear the fetcher buffer
3. subscribes 
4. send metadata update

Major Changes

Consumer Poll Changes

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