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I think the definition of availability is due to Brewer. The weird part of the 'theorem' due to Lynch and Gilbert is the definition ood consistency: in I recall correctly, it's linearizability, which is somewhat stronger than any guarantee that and DB actuality makes.



> it's linearizability, which is somewhat stronger than any guarantee that and DB actuality makes.

Isn't that equivalent to serializability, which is a guarantee that lots of DBs offer (though you can choose weaker ones instead.)


Spanner offers "external consistency", which is similar to linearizability.

CockroachDB offers serializability (as the default isolation level). Most other SQL databases offer serializability as their highest isolation level, but default to something weaker.

Serializability and linearizability are not equivalent, although it's not always easy to devise a scenario in which the differences are apparent. The "comments" tests in Aphyr's Jepsen analysis of CockroachDB is one such scenario: http://jepsen.io/analyses/cockroachdb-beta-20160829#comments


Linearizability is stronger; see the 'definition of linearizability' in https://en.wikipedia.org/wiki/Linearizability

Note: its been so long since I dealt with these things that I can't remember what the difference means in practice. :-)




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