Unlike the mongo extension, pecl/mongodb is developed atop of » libmongoc and » libbson and provides a minimal API for core driver functionality: commands, queries, writes, connection management and BSON serialization.

Userland PHP libraries that depend on mongodb may provide higher level APIs, such as query builders, individual command helper methods, and GridFS. This separation of concerns will allow mongodb to focus on essential features for which an extension implementation is paramount for performance.