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While I'm not familiar with Spanner's inner workings, I would guess that they recommend 3 instances for quorum establishment in case a region becomes unreachabl

by edaemon 10y ago

While I'm not familiar with Spanner's inner workings, I would guess that they recommend 3 instances for quorum establishment in case a region becomes unreachable. If that's the case, using fewer than 3 instances could cause major problems.

dragonwriter 10y ago
Since Spanner currently only supports single-region deployments, it clearly isn't recommended as protection against a region becoming unavailable. It may be recommended as protection against an availability issue on an instance, though, which is, after all, a big reason why you'd want a distributed DB in production.
- inlined 10y ago
  Even within a single region you can put three nodes in different zones.
- edaemon 10y ago
  I suppose the loss of a region doesn't apply (yet), but yes, the quorum requirement would still apply even if you only had instances in a single region.