In version 9i ORACLE introduce automatic undo management along with manual management. So one can use either automatic or manual management but not both at a time. The new method freed DBA from periodical undo management and tuning. In also facilitate the DBA to specify how long undo information is stored after a commit occur. This feature eliminate the "snapshot too old" error of long running queries and also support ORACLE flashback queries.
Create Undo Tablespace
CREATE UNDO TABLESPACE UNDOTBS DATAFILE '/u01/undotbs01_01.dbf'
SIZE 1024M BLOCKSIZE 16K;
alter system set undo_tablespace='UNDOTBS' scope=both;
Enabling Automatic Undo Management
UNDO_MANAGEMENT = AUTO -- Default is MANUAL
UNDO_TABLESPACE = undotbs_01 -- The name of the undo tablespace.
UNDO_RETENTION = 900 -- The time undo is retained. Default is 900 seconds.
UNDO_SUPPRESS_ERRORS = TRUE -- Suppress errors when MANUAL undo admin SQL statements are issued.
Please set the following parameters
-- Dynamic Parameters.
ALTER SYSTEM SET UNDO_TABLESPACE=UNDOTBS_02;
ALTER SYSTEM SET UNDO_RETENTION=1800;
ALTER SYSTEM SET UNDO_SUPPRESS_ERRORS=FALSE;
-- Static Parameters.
ALTER SYSTEM SET UNDO_MANAGEMENT=AUTO SCOPE=SPFILE;
Maintenance of Undo Tablespace
-- Add a datafile.
ALTER TABLESPACE undotbs_01 ADD DATAFILE '/u0/undo0102.dbf'
AUTOEXTEND ON NEXT 1M MAXSIZE UNLIMITED;
-- Resize an undo datafile.
ALTER DATABASE DATAFILE '/u0/undo0102.dbf' RESIZE 10M;
-- Perform backup operations
ALTER TABLESPACE undotbs_01 BEGIN BACKUP;
ALTER TABLESPACE undotbs_01 END BACKUP;
-- Drop an undo tablespace.
DROP TABLESPACE undotbs_01;
Sometimes the undo tablespace become too big to manage. In such case you can resize the datafiles or create a new undo tablespace in another disk location
- Resize an undo datafile.
ALTER DATABASE DATAFILE '/u0/undo0102.dbf' RESIZE 10M;
-- create new undo tablespace and drop the old one
CREATE UNDO TABLESPACE UNDOTBS DATAFILE '/u0/undotbs01_01.dbf' SIZE 1024M BLOCKSIZE 16K;
ALTER SYSTEM SET undo_tablespace='UNDOTBS' scope=both;
DROP TABLESPACE UNDOTBS1 INCLUDING CONTENTS AND DATAFILES;
Monitoring Undo Tablespace
You may use the following dictionary viewers:
V$UNDOSTAT
V$ROLLSTAT
V$TRANSACTION
DBA_UNDO_EXTENTS
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