Subject:            Redo Log Guidelines
Last Revision Date: 11 September 1994
Author:Lan Nguyen                                                         



CREATE DATABASE COMMAND
-----------------------

    o   Two Redo Logs are created at database creation time.  Redo
        Logs are specified in the CREATE DATABASE statement, two
        small Redo Logs are created in order to open the database.

    o   At least two Redo Logs are required to start the database.

INIT.ORA PARAMETERS
-------------------

    o   MAXLOGFILES in the CREATE DATABASE statement sets the
        absolute maximum number of Redo Log files.

    o   The ORACLE limit for MAXLOGFILES is 255.

    o   The INIT.ORA parameter LOG_FILES sets the current maximum
        number of Redo Logs.  LOG_FILES can temporarily reduce
        the limit set by MAXLOGFILES, but it cannot raise
        MAXLOGFILES.  If neither MAXLOGFILES or LOG_FILES is used,
        the default number of Redo Logs is 255.

SIZING
------

    o   There are no benefits to having different sized Redo Logs.

    o   The minimum size of a Redo Log is 50K.  There is no
        maximum size.

    o   In general larger Redo Logs

        -   Will take longer to fill
        -   Fewer Checkpoints will occur
        -   Archiving will be done less often
        -   Instance recovery may take longer depending on the
            Log_Checkpoint_Interval

LOCATION
--------

    o   Log files should be placed on different storage devices
        from those containing the database files for two reasons:

        1)  To reduce the risk of losing all Database and Redo Logs
            files in the event of media failure.

        2)  To reduce disk contention (during time of high database
            activity the log file is frequently accessed.)

    o   All Redo Log files may remain on the same storage device
        since the RDBMS only writes to one file at a time.

ARCHIVILOG MODE
---------------

    o   The database should run in ARCHIVELOG mode to maximize
        protection from media failure.

    o   The Redo Logs operatate in a circular fashion.  If running
        in ARCHIVELOG mode, additional Redo Logs may be needed
        to prevent Redo Log wrapping before the Redo Logs are
        archived.

                                                                          c