Previously in Jepsen, we discussed Redis. In this post, we’ll see MongoDB drop a phenomenal amount of data. See also: followup analyses of 2.6.7 and 3.4.0-rc3.

MongoDB is a document-oriented database with a similar distribution design to Redis. In a replica set, there exists a single writable primary node which accepts writes, and asynchronously replicates those writes as an oplog to N secondaries. However, there are a few key differences.