Advantages of automatic revocation Management in Oracle9i

In Oracle9i, Oracle renamed the rollback segment and uses it as the log for revocation. In traditional operations, the rollback segment stores the revocation information of the exchange until the system sends a response or rollback statement.

Manual Revocation Management is still used in Oracle9i, but most Oracle DBAs have chosen a new automatic method, which allows them to be freed from conventional revocation management tasks and adjustments.

The most important thing is that automatic revocation management allows DBA to specify the time needed to retain the revocation information after submission to prevent "snapshot too old" errors during long queries. You can set the UNDO_RETENTION parameter to implement this process. The default value of this parameter is 900 seconds (15 minutes), but you can set this parameter to ensure that Oracle retains the UNDO log.

Without defining and managing rollback segments, you can simply specify an undo tablespace to relieve the burden on Oracle9i.

Automatic undo management requires a local undo tablespace, which is used to store undo segments. All you need is to create an undo tablespace, set UNDO_MANAGEMENT = AUTO, and connect to the database. When an example is started, Oracle automatically selects the first available undo tablespace.

CREATE UNDO TABLESPACE　 ts_undoDATAFILE　 '/u01/oradata/prod/ts_undo.dbf'SIZE 2M REUSE AUTOEXTEND ON;Alter system set undo_tablespace=ts_undo;Alter system set undo_management=auto;

Once an undo tablespace has been created, you can use the following new Oracle9i query to view the Undo information.

V$UNDOSTAT V$ROLLSTAT V$TRANSACTION DBA_UNDO_EXTENTS

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