Concurrency Control
    Lock Modes
    Lock Granularity
            (Different storage engines can support different levels of granularity.)
        Lock Acquisition Order
            (discuss lock acquisition order)
            (mention risk of deadlocks motivation)
        Replication State Transition Lock (RSTL)
        Parallel Batch Writer Mode Lock (PBWM)
        Global Lock
        Database Lock
        Collection Lock
        Document Level Concurrency Control
            (Explain WT's optimistic concurrency control, and why we do not need document locks in the MongoDB layer)
        Mutexes
        FCV Lock
    Two-Phase Locking
        (We use this for transactions? Explain)
    Replica Set Transaction Locking
        (TBD: title of this section -- there is some confusion over what terminology will be best understood)
        (Stashing and unstashing locks for replica set level transactions across multiple statements.)
        (Read's IS locks are converted to IX locks in replica set transactions.)
    Locking Best Practices
        Network Calls
            (i.e., never hold a lock across a network call unless absolutely necessary)
        Long Running I/O
            (i.e., don't hold a lock across journal flushing)
        FCV Lock Usage