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Oracle Core: Essential Internals for DBAs and Developers by Jonathan Lewis

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Redo Simplicity

The way we handle redo is quite simple: we just keep generating a continuous stream of redo records and pumping them as fast as we can into the redo log, initially into an area of shared memory known as the redo log buffer. Eventually, of course, Oracle has to deal with writing the buffer to disk and, for operational reasons, actually writes the “continuous” stream to a small set of predefined files—the online redo log files. The number of online redo log files is limited, so we have to reuse them constantly in a round-robin fashion.

To protect the information stored in the online redo log files over a longer time period, most systems are configured to make a copy, or possibly many copies, of each file as it becomes full before ...

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