What is the purpose of TrueTime in Spanner?

TrueTime is a globally synchronized clock API that Spanner uses to assign commit timestamps to transactions. Instead of returning a single instant, TrueTime returns an interval [earliest, latest] that is guaranteed to contain the actual current time, using GPS and atomic clock references distributed across Google's data centers.

Spanner uses this bounded uncertainty to enforce external consistency: before committing a write, it waits out the remaining uncertainty window ("commit wait") so that any transaction that starts after another one commits is guaranteed to see a later timestamp. This lets Spanner order transactions correctly across data centers without needing a central coordinator for every commit, which is what makes global strong consistency practical at low latency.

Invest now in Acorns!!! 🚀
Join Acorns and get your $5 bonus!

Acorns is a micro-investing app that automatically invests your "spare change" from daily purchases into diversified, expert-built portfolios of ETFs. It is designed for beginners, allowing you to start investing with as little as $5. The service automates saving and investing. Disclosure: I may receive a referral bonus.

Invest now!!! Get Free equity stock (US, UK only)!

Use Robinhood app to invest in stocks. It is safe and secure. Use the Referral link to claim your free stock when you sign up!.

The Robinhood app makes it easy to trade stocks, crypto and more.

Webull! Receive free stock by signing up using the link: Webull signup.