這個特性將對於臨時表的UNDO信息分離出去，獨立存儲在臨時表空間中，這就減少了對於UNDO段的使用。這個特性完全無損Oracle的事務一致性，但是卻得到了空間縮減的好處。
下面用實驗測試下效果：
SQL> show parameter temp_undo_enabled;
temp_undo_enabled boolean FALSE
SQL> set autot traceonly statistics
SQL> create global temporary table test as select * from dba_tables where 1=0;
Table created.
SQL> insert into test select * from dba_tables;
2108 rows created.
Statistics
----------------------------------------------------------
782 recursive calls
521 db block gets
25061 consistent gets
9 physical reads
29384 redo size
865 bytes sent via SQL*Net to client
962 bytes received via SQL*Net from client
3 SQL*Net roundtrips to/from client
22 sorts (memory)
0 sorts (disk)
2108 rows processed
SQL> update test set table_name=lower(table_name);
2108 rows updated.
Statistics
----------------------------------------------------------
12 recursive calls
2742 db block gets
355 consistent gets
0 physical reads
299640 redo size
865 bytes sent via SQL*Net to client
965 bytes received via SQL*Net from client
3 SQL*Net roundtrips to/from client
1 sorts (memory)
0 sorts (disk)
2108 rows processed
SQL> conn / as sysdba
Connected.
SQL> alter session set temp_undo_enabled=true;
Session altered.
SQL> set autotrace traceonly statistics;
SQL> insert into test select * from dba_tables;
2108 rows created.
Statistics
----------------------------------------------------------
25 recursive calls
528 db block gets
11812 consistent gets
0 physical reads
272 redo size
850 bytes sent via SQL*Net to client
962 bytes received via SQL*Net from client
3 SQL*Net roundtrips to/from client
2 sorts (memory)
0 sorts (disk)
2108 rows processed
SQL> update test set table_name=lower(table_name);
2108 rows updated.
Statistics
----------------------------------------------------------
0 recursive calls
129 db block gets
97 consistent gets
0 physical reads
0 redo size
857 bytes sent via SQL*Net to client
965 bytes received via SQL*Net from client
3 SQL*Net roundtrips to/from client
1 sorts (memory)
0 sorts (disk)
2108 rows processed