There’s a difference between causality ordering and global total ordering. Lamport timestamps and vectors help you get causality ordering. This is not enough f

There’s a difference between causality ordering and global total ordering. Lamport timestamps and vectors help you get causality ordering. This is not enough for Spanner. Spanner needs total global ordering. A perfect real time clock would let you achieve total ordering. As you’ve pointed out, Spanner relies on a clock. However, no clock is perfect, so Spanner has to account for that margin of error. And because of its clock (TrueTime) that margin of error is small enough to keep latency low.