> Google faced the clock synchronization problem at an unprecedented scale with Spanner, its globally distributed database. They needed strong consistency guarantees across data centers spanning continents, which requires knowing the order of transactions.

> Here’s a video of me explaining this.

Do you need a video? Do we need a 42 minute video to explain this?

I generally agree with Feynman on this stuff. We let explanations be far more complex than they need to be for most things, and it makes the hunt for accidental complexity harder because everything looks almost as complex as the problems that need more study to divine what is actually going on there.

For Spanner to be useful they needed a high transaction rate and in a distributed system that requires very tight grace periods for First Writer Wins. Tighter than you can achieve with NTP or system clocks. That’s it. That’s why they invented a new clock.

Google puts it this way:

Under external consistency, the system behaves as if all transactions run sequentially, even though Spanner actually runs them across multiple servers (and possibly in multiple datacenters) for higher performance and availability.

But that’s a bit thick for people who don’t spend weeks or years thinking about distributed systems.