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Chapter 5 - Automatic Storage Management

Automatic Undo Management

Oracle Database 10g remembers optimal undo settings to avoid repeated ramp ups and performance problems during instance restart, database migration, and switching the undo tablespace. After a system restart or an undo tablespace switch, Oracle Database 10g decides how many undo segments to place online based on existing data stored in the AWR.

The Undo Advisor analyzes the undo usage. In AUM mode, the advisor suggests optimal undo tablespace size to support the longest running queries. If AUM is not used, it suggests undo tablespace size for a given retention period and the retention period for a given undo tablespace size.

Resumable space allocation, introduced in Oracle 9i, is for all tablespaces at the session level. Database operations are suspended when an out-of-space condition is encountered. These suspended operations automatically resume when the error condition disappears. In Oracle Database 10g, this can be enabled at the instance level. Besides this improvement, automatic alert notification is sent when an operation is suspended.

This feature can be enabled by the SQL command.

ALTER SYSTEM SET RESUMABLE_TIMEOUT = <value in seconds>;
(Substitute 3600 for 1 hour)

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