Syntax option:

    NUMBER OF USERS IS number-users

    Limits the maximum number of users allowed to access the database
    at one time. Specify this clause only if the database named in
    the ALTER DATABASE statement refers to a multifile database.

    The default is 50 users. After the maximum is reached, the next
    user who tries to invoke the database receives an error message
    and must wait. The maximum number of users you can specify is
    16368 and the minimum is 1 user.

    Note that number of users is defined as the number of active
    attachments to the database. Therefore, if a single process
    is running one program but that program performs 12 attach
    operations, the process is responsible for 12 active users.

    If you use the ALTER DATABASE statement to change the current
    number of users, the change is not journaled. Therefore, back up
    your database before making such a change.