Threshold=disk-blocks
    Nothreshold

    This qualifier can be used only when extensible journaling is
    enabled. It cannot be used with fixed-size journaling.

    The Threshold qualifier sets an approximate limit on the size
    of the active .aij file. When the size of the active .aij file
    exceeds the threshold, you cannot initiate new transactions
    until the backup process finishes backing up and truncating
    (resetting) the active .aij file. During the backup operation,
    existing transactions can continue to write to the .aij file.
    Before new transactions can start, all activity issuing from
    existing transactions (including activity occurring after the
    threshold is exceeded) must be moved from the active .aij disk
    file to the .aij backup file. At that time, the active .aij file
    will be completely truncated.

    If you use the default, the Nothreshold qualifier, each backup
    cycle will completely back up the active .aij file. Oracle
    Corporation recommends using the Nothreshold qualifier.

    An appropriate value for the Threshold qualifier depends on the
    activity of your database, how much disk space you want to use,
    whether backup operations will be continuous, and how long you
    are willing to wait for a backup operation to complete.

    See the Oracle Rdb7 Guide to Database Performance and Tuning for
    more information on setting SPAM thresholds.