If the keyword DEFAULT is used, the user-specific default
    transaction is started. This default is defined in the profile
    for the current session user. If none is specified, a READ ONLY
    transaction will be started.

    SQL> CREATE PROFILE READ_USERS
    cont>   DEFAULT TRANSACTION READ ONLY WAIT 10;
    SQL> ALTER USER JONES PROFILE READ_USERS;

    A START DEFAULT TRANSACTION statement executed by JONES will
    start a READ ONLY WAIT 10 transaction.

    For information on profiles see the ALTER and CREATE PROFILE
    statements.