CP database (in the CAP theorem sense), distributed transactions via Paxos. Most popular databases (Cassandra, Riak, et al) are AP* systems. CockroachDB is an interesting project in progress that aims to be a CP system from my understanding.
EDITED: seancribbs corrected my acronym spelling in the early morning;
*CA - DOES NOT EXIST, what I wrote initially was completely wrong
EDITED: seancribbs corrected my acronym spelling in the early morning; *CA - DOES NOT EXIST, what I wrote initially was completely wrong