%*local*% and %*available*% are most permissive %*majority*% guarantees that the data has been acknowledged by a majority %*linearizable*% provides additional guarantees over majority to avoid returning stale data. Introduced in MongoDB 3.4 to satisfy the *Jepsen* test framework. %*snapshot*% may be used with majority-committed transactions to guarantee that reads within that transaction use a snapshot of majority-committed data “In plain English, under linearizability, writes should appear to be instantaneous. Imprecisely, once a write completes, all later reads (where “later” is defined by wall-clock start time) should return the value of that write or the value of a later write. Once a read returns a particular value, all later reads should return that value or the value of a later write.” https://docs.mongodb.com/manual/reference/read-concern-local/ https://docs.mongodb.com/manual/reference/read-concern-available/ https://docs.mongodb.com/manual/reference/read-concern-linearizable/ https://stackoverflow.com/a/44763501/162228 http://www.bailis.org/blog/linearizability-versus-serializability/ https://docs.mongodb.com/manual/reference/read-concern-snapshot/