… but on a different account.
Exactly.
Now for the benchmarks I think my solution would be interesting only with heavy works inside the transaction. I am building games (hobby project) so we update a big game state. I bet having only one GenServer call (to get_and_update_mutli) is faster for many simple updates (especially for simple additions like bank account balances obvioulsy – that is just test stuff).
If I find time for that I will setup a scenario and calculate different pairs of concurrency/update-time where a mutex would be better.
. It is the result of running 
