Yeah looking at that is what prompted this question. Are the events in order? If so: the index for an event in the bitmap is constant, so if you realize you need to save an event that wasn't previously being saved, how do you insert it to keep order? Do you break all previously saved data by changing all the following indexes? Or are the events not in order, which could make it harder to find if an event is already in it (and just generally be confusing)? Managing a long list of events like this given that it is used for persistent state seems like an interesting process challenge.