UNDO tablespace increasing and not release space

UNDO tablespace increasing/growing and not release space

Applies to: 

Oracle Database 10gR2

Description:

Undo tablespace start growing abnormally. UNDO_RETENTION parameter is set to 900 seconds, but undo data did not release the space. After doing some research work, I found the following solution:

Solution:

Set the following hidden parameter in init.ora file and check the free space in undo tablespace after 3-4 Hrs.

_smu_debug_mode=33554432

or

SQL> Alter system set "_smu_debug_mode" = 33554432;

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