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 composed of two different
    types of blocking ASTs: those generated externally and those
    generated internally.

    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. This algorithm
    serves as an optimistic code optimization; the process, assuming
    it would eventually receive a blocking AST for the particular
    lock, executes the blocking AST routine. The Performance Monitor
    does not differentiate between these two types of blocking ASTs.