THIS IS A TEST INSTANCE. ALL YOUR CHANGES WILL BE LOST!!!!
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For a map, sets of removed and updated keys need to be maintained. Again, if there were any clear() or “black-box” operations (such as entrySet() with potential replace/remove), then the full map is snapshotted.
As an optimization, map.clear() call can remove the entry completely.
Value, Aggregating and Reducing states
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