Waiting Out the Doubt

Spanner's TrueTime returns an interval rather than a single instant, because the true time lies somewhere inside a bounded uncertainty window. To get externally consistent commit ordering, what does a read-write transaction do with that uncertainty before it is reported as committed?

It relies on the Paxos leader's log position alone, since replicated log order already gives a global ordering of transactions

It waits out the uncertainty window around its commit timestamp, so any later transaction gets a larger one

It picks the earliest instant in the interval, which makes the timestamp conservative and removes the need to wait

It blocks until the local time daemon reports a fresh sync, which shrinks the interval to a single point