DB Wiki

By default when a database is created using DBCA, the database auditing parameter will be turned on.

SQL> show parameter audit_trail

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
audit_trail                          string      DB

This means whenever a connection is made to the database, an entry is logged in the Audit Trail. Therefore the table sys.aud$ can grow very quickly and on web applications will affect performance

You can turn this off by entering the following as SYS user …

SYS> NOAUDIT CREATE SESSION WHENEVER SUCCESSFUL;

Noaudit succeeded.

This still means that failed logins are audited.