Setting the Minimum Undo Retention Period

You specify the minimum undo retention period (in seconds) by setting the UNDO_RETENTION initialization parameter. As described in "About the Undo Retention Period", the current undo retention period may be automatically tuned to be greater than UNDO_RETENTION, or, unless retention guarantee is enabled, less than UNDO_RETENTION if space in the undo tablespace is low.

To set the minimum undo retention period:

• Do one of the following:

  • Set UNDO_RETENTION in the initialization parameter file.

    UNDO_RETENTION = 1800
    

  • Change UNDO_RETENTION at any time using the ALTER SYSTEM statement:

    ALTER SYSTEM SET UNDO_RETENTION = 2400;
    

The effect of an UNDO_RETENTION parameter change is immediate, but it can only be honored if the current undo tablespace has enough space.