The dominance of the commodity machine model for data centers is so complete that one forgets that there was ever any other viable choice. But IBM, for one, is still selling lots of mainframes. Nevertheless the world I live in is built on top of data centers that contain a lot of commodity class machines. These machines have a nasty habit of failing on a fairly regular basis. So when I think about the CAP theorem I think about it in the context of a data center filled with a bunch of not completely reliable boxes.

In that case partition tolerance (which, as I explain below, ends up meaning tolerance of machine failure) is a requirement. So in designing frameworks for the data centers I work with the CAP theorem makes me choose between exactly two choices - do I want consistency or availability?

My belief is that for the vast majority of developers, at least for the immediate future, they need to choose consistency.

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