UNDO_RETENTION

Parameter type	Integer
Default value	900
Parameter class	Dynamic: ALTER SYSTEM
Range of values	0 to 232-1 (max value represented by 32 bits)
Real Application Clusters	Multiple instances must have the same value.

UNDO_RETENTION specifies (in seconds) the amount of committed undo information to retain in the database. You can use UNDO_RETENTION to satisfy queries that require old undo information to rollback changes to produce older images of data blocks. You can set the value at instance startup.

The UNDO_RETENTION parameter works best if the current undo tablespace has enough space for the active transactions. If an active transaction needs undo space and the undo tablespace does not have any free space, then the system will start reusing undo space that would have been retained. This may cause long queries to fail. Be sure to allocate enough space in the undo tablespace to satisfy the space requirement for the current setting of this parameter.

See Also: Oracle9i SQL Reference for more information about creating undo tablespaces