Managing the Redo Log

Multiplexing the Redo Log

Oracle recommends that you multiplex the redo log. Multiplexing provides better protection for data in the case of instance or media failure.

To multiplex your redo log, you must add members to each redo log group. It is not required that redo log groups be symmetrical, but Oracle recommends that your groups all have the same number of members. A database must have a minimum of two redo log groups.

To multiplex the redo log:

1. Go to the Database Home page.

   See "Accessing the Database Home Page".

2. At the top of the page, click the Server link to view the Server subpage.

3. In the Storage section, click Redo Log Groups.

   The Redo Log Groups page appears.

   For more information about a page, at any time, click Help.

4. Select a group and click Edit.

   The Edit Redo Log Group page appears.

5. Click Add.

   The Add Redo Log Member page appears.

6. In the File Name field, enter a file name for the new redo log member.

   For example, if your existing member file name is REDO01.log, then you might name this member REDO01a.log.

7. In the File Directory field, enter the file directory or accept the default.

   You can create this file in the same directory, but it is recommended that you store members on separate disk drives. That way, if there is a drive failure, you still have access to one member.

8. Click Continue, and then click Apply to accept your changes.

   A confirmation message appears.

9. At the top of the page, click the Redo Log Groups link to return to the Redo Log Groups page.

10. Repeat Step 4 through Step 9 for every existing log group.

Switching a Log File

When a log switch occurs, the log writer (LGWR) process stops writing to the current redo log group and starts writing to the next available redo log group. You can force a log switch to make the current redo group inactive and available for redo log maintenance operations. For example, you might want to drop the current redo group, but are not able to do so until the group is inactive. You may also want to force a log switch if the current redo group needs to be archived at a specific time before the members of the group are completely filled. This option is useful in configurations with large redo log files that take a long time to fill.

To switch a log file:

1. Go to the Database Home page.

   See "Accessing the Database Home Page".

2. At the top of the page, click the Server link to view the Server subpage.

3. In the Storage section, click Redo Log Groups.

   The Redo Log Groups page appears.

   For more information about a page, at any time, click Help.

4. In the Actions list, select Switch logfile, and then click Go.

   A confirmation message appears. The status of the group that had been Current changes to Active, and the status of the next group in the list changes from Inactive to Current.