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by genneth
2116 days ago
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In reality the application running on top of the database wants C-kinda-A. https://research.google/pubs/pub45855/ > Despite being a global distributed system, Spanner claims to be consistent and highly available, which implies there are no partitions and thus many are skeptical. Does this mean that Spanner is a CA system as defined by CAP? The short answer is “no” technically, but “yes” in effect and its users can and do assume CA. The point is that if my application will actually go down anyway if the WAN craps out, then really, I don't actually need P. The application would also be significantly simpler if it assumes that if the application can work, then the DB is also up. And one seems that realistic systems built on Spanner simply assume CA and then get on with life... |
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Can you guarantee no further modification to the data in the database occurs when the WAN craps out? What happens to in flight requests, batch/scheduled jobs, etc.? There's no situation where your application continues modifying the contents of the database even when there's no WAN link?
I've seen very few real world services where there is a 0% chance of data changing just because the application servers can no longer talk with clients but can still talk with the database. What happens when those databases try to rejoin the cluster and their data is now inconsistent, if you did not take into account partition tolerance?