The number of times a DAPF-initiated buffer fetch attempt was
    successful in fetching the buffer. This is possible only if an
    EX lock can be obtained for the whole buffer. A successful DAPF
    fetch may actually issue an asynchronous read or simply ensure
    that a buffer that was already in the buffer pool now moves to
    the front of the LRU queue. In the latter case, the buffer then
    becomes least likely to be removed from the buffer pool.