> However, the number of shards that have possibilities of state-based aborts is known before the transaction begins, and since the same values are being sent everywhere, you can always use standard network broadcast techniques to bring the complexity back to O(n)

Ah, good point. That assumes the workers are within broadcast range, but you'll want that anyway for speed. This means a worker will have to push values to other workers, so they'll maintain a queue of these then?

Anyway, thanks for the responses. Like I said, not my field at all, but really fun stuff to ponder.