Google Cloud Platform for Developers

TrueTime and linearization

In order for a system to truly provide strong consistency guarantees, its operations must be linearizable, meaning all nodes can agree on the exact ordering of events. This becomes extremely challenging in distributed systems, as the nodes must ensure their internal clocks are synchronized to a very small margin of error. To solve this, Google Cloud datacenters are equipped with specialized atomic clocks that are regularly synchronized with each other using GPS. These clocks are used to implement TrueTime, which allows Cloud Spanner nodes to determine the current time down to a very fine resolution.

Even with specialized hardware, system time will never be truly exact. TrueTime brings the margin of error down to ...