This recording of the changes can be
replayed to reproduce all the transaction??™s changes later, if they are needed
due to a failure.
To provide maximum performance without risking transactional integrity, Oracle
writes out only the redo information. When a user commits a transaction,
Oracle guarantees that the redo for those changes writes to the redo logs on disk.
The actual changed database blocks will be written out to the datafiles later. If a
failure occurs before the changed blocks are flushed from the cache to the
datafiles, the redo logs will reproduce the changes in their entirety. Because the
slowest part of a computer system is the physical disk, Oracle??™s fast-commit
approach minimizes the cost of committing a transaction and provides maximum
risk-free performance.
Flashback
In Oracle9i, rollback segments were also used to implement a feature called Flashback
Query. Remember that rollback segments are used to provide a consistent
image of the data in your Oracle database at a previous point in time. With Flashback
Query, you can direct Oracle to return the results for a SQL query at a specific
point in time.
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