Mongo 3.2 introduces new query option: readConcern. It allows to read only these changes that have been already committed to the majority of secondary instances.
It prevents stale reads - a situation in which a change has been committed on the primary (and read from it), but due to the network partition a new primary is elected and the change is rolled back.
We should use this new option (together with w:majority implemented in
OAK-3554) when running Oak on MongoDB replica set.