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When the user polls() for new offsets, if consumer2 has not finished, then only offsets from buffer2 will be sent to the user. After each poll(), buffer2 will be emptied of its contents after its records have been returned to the user to free up memory. (Note that if some offsets in buffer2 has not been committed yet, then those offsets will still be kept.) However, if consumer2 has terminated, then all offsets that has accumulated in buffer1 will also be sent (with both buffer2 and buffer1 being discarded, now that both are no longer used).   In this manner, we could also guarantee ordering for the user.

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