But you don't have to keep redundant copies around forever. Immutability means nothing in the past can change, which means it's perfectly fine for future entrie

But you don't have to keep redundant copies around forever. Immutability means nothing in the past can change, which means it's perfectly fine for future entries to reference old values. New rows can essentially be deltas, much like version control systems. I disagree that Datomic necessarily grows huge. I'm just saying don't use it if you know you're going to be storing terabytes and you don't have enough disk space to handle it without needing to truncate data with regular intervals.