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A log switch occurs when the log writer (LGWR) finishes writing redo entries to the current online redo log file group and starts writing to the next online redo log file group. By default, a log switch occurs automatically when the current online redo log file group is full. A log switch can also be forced by executing the ALTER SYSTEM SWITCH LOGFILE; statement, regardless of whether or not the current online redo log file group is full.

The log writer (LGWR) is an Oracle background process. It is responsible for writing all the new entries that have been copied in the redo log buffer since the LGWR last wrote the entries to a redo log file. The log writer should write the entries of the redo log buffer fast enough, so that buffers are immediately available for new entries.

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Oracle’s password aging and expiration feature ensures that the password of a user account expires after a specified number of days. The user or the database administrator must change the password once it has expired. The PASSWORD_LIFE_TIME parameter is used to specify the number of days after which a user account’s password expires.

Oracle’s password complexity verification feature ensures that a password is too complex to be guessed easily. The complexity of a password can be verified before a user can set the password for his account. The PASSWORD_VERIFY_FUNCTION parameter specifies a PL/SQL script that is used to verify the complexity of a password. Oracle provides a default PL/SQL script for this purpose. However, users can also create their own scripts. For example, a script can be created to verify that a password has a minimum length of four characters, the password is not the same as the account’s name, the password has at least one alphabetical, one numeric, and one punctuation mark character, the password is not a simple or obvious word, and the password differs from the previous password by at least three characters.