CAP in the Wild
Some partition-tolerant databases can be tuned to be more or less consistent or available on a per-request basis. Riak works like this, allowing clients to decide at request time what level of consistency they require. The other databases in this book largely occupy one corner or another of the CAP trade-off triangle.
Redis, PostgreSQL, and Neo4J are consistent and available (CA); they don’t distribute data and so partitioning is not an issue (though arguably, CAP doesn’t make much sense in non-distributed systems). MongoDB and HBase are generally consistent and partition tolerant (CP). In the event of a network partition, they can become unable to respond to certain types of queries (for example, in a Mongo replica set you ...
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