Scaling consistency - the master-slave model
As distributed systems have become more commonplace, the need for higher capacity distributed databases has grown. Many distributed databases still attempt to maintain ACID guarantees (or in some cases only the consistency aspect, which is the most difficult in a distributed environment), leading to the master-slave architecture.
In this approach, there might be many servers handling requests, but only one server can actually perform writes so as to maintain data in a consistent state. This avoids the scenario where the same data can be modified via concurrent mutation requests to different nodes. The following diagram shows the most basic scenario:
However, we still have not solved the availability ...
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