Syntax option:

    THRESHOLD IS number-pages PAGES

    This number represents the number of sequential buffer accesses
    that must be detected before prefetching is started. The default
    is four buffers.

    If you specify the THRESHOLD option, you must have also specified
    the DETECTED ASYNC PREFETCH clause. You receive an error if you
    attempt to specify the THRESHOLD option with the ASYNC PREFETCH
    clause.