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Oracle9i introduced automatic management of rollback segments. In previous
versions of the Oracle database, DBAs had to explicitly create and manage
rollback segments. In Oracle9i, youhad the option of specifying automatic management
of all rollback segments through the use of an undo tablespace. With
automatic undo management, you can also specify the length of time that you
want to keep undo information; this feature is very helpful if you plan on using
flashback queries, discussed in the following section. Oracle Database 10g added
an undo management retention time advisor.
Oracle at Work | 79
Fast commits
Because redo logs are written whenever a user commits an Oracle transaction, they
can be used to speed up database operations. When a user commits a transaction,
Oracle can do one of two things to get the changes into the database on the disk:
??? Write all the database blocks the transaction changed to their respective
datafiles.
??? Write only the redo information, which typically involves much less I/O
than writing the database blocks.


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