Jepsen: Testing the Partition Tolerance of PostgreSQL, Redis, MongoDB and Riak

“Distributed systems are characterized by exchanging state over high-latency or unreliable links. The system must be robust to both node and network failure if it is to operate reliably–however, not all systems satisfy the safety invariants we’d like. In this article, we’ll explore some of the design considerations of distributed databases, and how they respond to network partitions.

IP networks may arbitrarily drop, delay, reorder, or duplicate messages send between nodes–so many distributed systems use TCP to prevent reordered and duplicate messages. However, TCP/IP is still fundamentally asynchronous: the network may arbitrarily delay messages, and connections may drop at any time. Moreover, failure detection is unreliable: it may be impossible to determine whether a node has died, the network connection has dropped, or things are just slower than expected…”

http://www.infoq.com/articles/jepsen