Oracle7 Server Administrator's Guide

Creating Online Redo Log Groups and Members

You can create groups and members of online redo log files during or after database creation. If you can, plan the online redo log of a database and create all required groups and members of online redo log files during database creation. To create new online redo log groups and members, you must have the ALTER DATABASE system privilege.

In some cases, you might need to create additional groups or members of online redo log files. For example, adding groups to an online redo log can correct redo log group availability problems. A database can have up to MAXLOGFILES groups.

Creating Online Redo Log Groups

To create a new group of online redo log files, use either the Add Logfile Group property sheet of Server Manager, or the SQL command ALTER DATABASE with the ADD LOGFILE parameter.

The following statement adds a new group of redo logs to the database:

ALTER DATABASE

   ADD LOGFILE ('log1c', 'log2c') SIZE 500K;

Note: Fully specify filenames of new log members to indicate where the operating system file should be created; otherwise, the file is created in the default directory of the database server, which is operating system-dependent. If you want to reuse an existing operating system file, you do not have to indicate the file size.

Using the ALTER DATABASE statement with the ADD LOGFILE option, you can specify the number that identifies the group with the GROUP option:

ALTER DATABASE

   ADD LOGFILE GROUP 10 ('log1c', 'log2c') SIZE 500K;

Using group numbers can make administering redo log groups easier. However, the group number must be between 1 and MAXLOGFILES; do not skip redo log file group numbers (that is, do not number your groups 10, 20, 30, and so on), or you will consume unnecessary space in the control files of the database.

Creating Online Redo Log Members

In some cases, you might not need to create a complete group of online redo log files; the group may already exist, but not be complete because one or more members of the group were dropped (for example, because of a disk failure). In this case, you can add new members to an existing group.

To create new online redo log members for an existing group, use the Add Logfile Member property sheet of Server Manager, or the SQL command ALTER DATABASE with the ADD LOG MEMBER parameter.

The following statement adds a new redo log member to redo log group number 2:

ALTER DATABASE

   ADD LOGFILE MEMBER 'log2b' TO GROUP 2;

Notice that filenames must be specified, but sizes need not be; the size of the new members is determined from the size of the existing members of the group.

When using the ALTER DATABASE command, you can alternatively identify the target group by specifying all of the other members of the group in the TO parameter, as shown in the following example:

ALTER DATABASE

   ADD LOGFILE MEMBER 'log2c' TO ('log2a', 'log2b');

Note: Fully specify the filenames of new log members to indicate where the operating system files should be created; otherwise, the files will be created in the default directory of the database server.