102 - [Oracle 19C] Overview of Automatic Undo Management

 

 

Managing UNDO Data
Overview of Automatic Undo Management

 Oracle provides a fully automated mechanism for managing undo information and space.

 the database manages undo segments in an undo tablespace

 Automatic undo management is the default mode for a newly installed database. An auto extending undo tablespace named UNDOTBS1 is automatically created when you create the database with Database Configuration Assistant (DBCA).

 When the database instance starts, the database automatically selects the first available undo tablespace . If no undo tablespace is available, then the instance starts without an undo tablespace and stores undo records in the SYSTEM tablespace . This is not recommended, and an alert message is written to the alert log file to warn that the system is running without an undo tablespace

 

 

 

Space management for rollback segments is complex. Oracle strongly recommends leaving the database in automatic undo management mode.