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Can someone elaborate on this Witness system OP talks about?

I'm picturing a replicated, in-memory KV store where the value is some sort of version or timestamp representing the last time the object was modified. Cached reads can verify they are fresh by checking against this version/timestamp, which is acceptable because it's a network+RAM read. Is this somewhat accurate?

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I'm picturing the same, but my guess is that it's using a time-synced serializability graph or MVCC in some way.

However, even a "basic" distributed lock system (like a consistently-hashed in-memory DB, sharded across reliable servers) might provide both the scale and single source of truth that's needed. The difficulty arises when one of those servers has a hiccup.

It'd be a delicious irony if it was based on hardware like an old-school mainframe or something like that.

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