This field gives the number of blocking ASTs, sometimes referred
    to as blasts, delivered to Oracle Rdb by the lock manager. A
    blocking AST is delivered to the holder of a lock when a lock
    conflict is detected, which is a good indication of contention
    problems. When Oracle Rdb receives a blocking AST, it often
    demotes or releases a lock in an attempt to avoid unnecessary
    deadlocks.

    The number of blocking ASTs reported is actually comprised of two
    different types of blocking ASTs, those blocking ASTs externally
    generated and those blocking ASTs internally generated.

    An externally generated blocking AST occurs when a blocking AST
    is actually received by the process from the operating system in
    response to some lock conflict with another process. A blocking
    AST routine is executed and the Performance Monitor records the
    blocking AST activity.

    An internally generated blocking AST occurs when a lock-blocking
    AST routine is executed by the process in anticipation that
    the same work would have to be performed anyway if a blocking
    AST were to be received from the operating system, even when
    no blocking AST from the operating system actually occurred.
    This algorithm serves as an optimistic code optimization; it is
    assumed that the process would eventually receive a blocking
    AST for the particular lock, so it optimistically executes
    the blocking AST routine. The Performance Monitor does not
    differentiate between these two types of blocking ASTs.