Guaranteeing Undo Availability
We discussed the option to guarantee undo retention in the section titled “The Significance of the UNDO_RETENTION Parameter” earlier in this chapter. You can enable the guarantee option by specifying the RETENTION GUARANTEE clause for the undo tablespace when it is created or at a later period using the ALTER TABLESPACE statement. The UNDO_RETENTION parameter is valid only if the current undo tablespace has sufficient space.
If you have more than one undo tablespace, you can switch from one tablespace to another for running longer batch jobs or for maintenance purposes. This is analogous to using larger rollback segments in Oracle 8i for long-running queries. Because the UNDO_TABLESPACE initialization parameter ...
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