Specifies one, two, or three default threshold values for logical
    areas that contain the index in storage areas with uniform
    page formats. By setting threshold values, you can make sure
    that Oracle Rdb does not overlook a page with sufficient space
    to store compressed data. The threshold values (val1, val2,
    and val3) represent a fullness percentage on a data page and
    establish three possible ranges of guaranteed free space on the
    data pages.

    If you use data compression, you should use logical area
    thresholds to obtain optimum storage performance.

    You cannot specify the thresholds for the storage map attribute
    for any area that is a mixed page format. If you have a mixed
    page format, set the thresholds for the storage area using the
    ADD STORAGE AREA or CREATE STORAGE AREA clause of the ALTER
    DATABASE, CREATE DATABASE, or IMPORT statement.

    For more information about SPAM pages, see the Oracle Rdb Guide
    to Database Design and Definition.