When the group of redo log files is filled, it begins to write redo entries to the next group.
Figure 1-4 shows how a set of four redo log files can be multiplexed with four groups, each
group containing three members.
Chapter 1: Getting Started with the Oracle Architecture 31
Adding a member to a redo log group is very straightforward. In the alter database command,
we specify the name of the new file and the group to add it to. The new file is created with the
same size as the other members in the group:
alter database
add logfile member '/u05/oracle/dc2/log_3d.dbf'
to group 3;
If the redo log files are filling up faster than they can be archived, one possible solution is to
add another redo log group. Here is an example of how to add a fifth redo log group to the set of
redo log groups in Figure 1-4:
alter database
add logfile group 5
('/u02/oracle/dc2/log_3a.dbf',
'/u03/oracle/dc2/log_3b.dbf',
'/u04/oracle/dc2/log_3c.dbf') size 250m;
All members of a redo log group must be the same size. However, the log file sizes between
groups may be different. In addition, redo log groups may have a different number of members. In
the preceding example, we started with four redo log groups, added an extra member to redo log
group 3 (for a total of four members), and added a fifth redo log group with three members.
As of Oracle 10g, you can use the Redo Logfile Sizing Advisor to assist in determining the
optimal size for redo log files to avoid excessive I/O activity or bottlenecks.
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