Cassandra also does that without requiring the "magic" of a system you can only get from a single vendor and never buy. At the same time these walled gardens have come up free software has grown to fill the gaps
Spanner is unique in a lot of ways, but it still trades off consistency for speed.
The most unique thing about spanner is the use of globally synchronized clock timestamps to guarantee "comes before" consistency without the need to actually synchronize everything.
There is nothing stopping startups and open source developers from building the same thing in a few years. The missing ingredient is highly stable GPS and local time sources which will hopefully be available on cloud instances sometime soon. This is a new piece of hardware so it will be interesting to see if cloud providers make one available or use the opportunity to sell their own branded "service" version you can't buy. Unfortunately I think we'll see the latter far before the former, it it ever even exists. Without a highly stable timesource doing what spanner does will be completely impossible.
Yes spanner is special right now but that's even more reason to not go near it. Google has a complete monopoly on it, the strongest vendor lock in you can possibly have
Only "new" in the sense that it is currently not commonly offered, the devices themselves have been available for ages. (If you are a large enough customer you apparently can get at least some colo-facilities to provide you with the roof-access and cabling needed for the antennas). If cloud providers make precise time available I don't see much potential for locking you in with their specific way of providing it, as long as it ends up as precise system time in some way.
I'm saying I doubt they will ever offer it precisely because it will conflict with their paid offerings. The fact that it takes its hardware is a great excuse to not give your customers the option.
I know GPS time sources have been available forever but a fault tolent database needs a backup. The US GPS is incredibly reliable but there have been multiple issues with both Glonass and Galilio.
It sounds like Google has an additional time source making this possible, probably a highly miniaturized atomic clock, possibly on a single chip. There's no way they're running on GPS alone
Yes, they clearly say that they use atomic clocks in addition, but that's commercially available as well. Atomic clock for frequency stability short- to mid-term, GPS to keep it synced to global time. E.g. in many cases, mobile-phone base stations contain just such a setup, and the data-center versions should fit in a few HE.