They handle uncertainty by delaying the transaction commit. Suppose you commit a transaction and at that moment, the error bar for time (on the server that hand

They handle uncertainty by delaying the transaction commit. Suppose you commit a transaction and at that moment, the error bar for time (on the server that handles your transaction) is 4 ms. The server will wait 4 ms to tell you the transaction completed. The result is that if two transactions commit near-simultaneously, it's random which will be assigned a lower timestamp, but guaranteed that no one will observe either transaction until after the timestamp at which that transaction is deemed to have committed. Basically, they handle the window of uncertainty by pausing access to the affected rows so that no one can peek into the window.