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Multiplexing redo log files
Oracle defines specific terminology to describe how it manages redo logs. Each Oracle
instance uses a thread of redo to record the changes it makes to the database. A
thread of redo is composed of redo log groups, which are composed of one or more
redo log members.
Logically, youcan think of a redo log group as a single redo log file. However, Oracle
allows youto specify multiple copies of a redo log to protect the all-important
integrity of the redo log. By creating multiple copies of each redo log file, you protect
the redo log file from disk failure and other types of disasters.
Figure 2-5 illustrates a thread of redo with groups and members. The figure shows
two members per group, with each redo log mirrored.
Figure 2-5. A thread of redo
member 1 member 2
Group 1
member 1 member 2
Group 2
member 1 member 2
Group 3
Members in a group are identical
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44 | Chapter 2: Oracle Architecture
When multiple members are in a redo log group, Oracle maintains multiple copies of
the redo log files.


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