8.1 How Cache Works
    Before tuning the server, you need to understand how the
    server uses cache.

    In general, increasing the cache size improves server
    performance. The server stores files temporarily in cache
    memory. A file in cache can be accessed quickly, because it
    does not have to be accessed from the disk.

    However, the performance of write operations improves
    until the volume of data written exceeds the write capacity
    of the current cache size. After the cache capacity is
    exceeded, the server has to reallocate cache buffers and
    performance declines.

    Because files for applications are stored on the VMS server,
    there is significant overhead in opening and closing files.
    To reduce this overhead, you can store open files in cache.
    Using cache for open files is called open file caching .
    Many personal computer applications open and close
    files repeatedly in rapid succession. If a file in the open
    file cache is opened soon after it is closed, the file can be
    reopened quickly, because the file's data structures have
    remained in the cache.