引數FAST_START_PARALLEL_ROLLBACK(ZT)

oracle手冊解釋

FAST_START_PARALLEL_ROLLBACK determines the maximum number of processes that can exist for performing parallel rollback. This parameter is useful on systems in which some or all of the transactions are long running.

Values:

FALSE indicates that parallel rollback is disabled

LOW limits the number of rollback processes to 2 * CPU_COUNT

HIGH limits the number of rollback processes to 4 * CPU_COUNT
系統預設：SQL> show parameter fast_start_parallel_rollback;

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
fast_start_parallel_rollback         string      LOW
今天突然出現很多並行程式，搞得系統IDLE急劇下降。手冊上指出當這個值是LOW,rollback的程式數就是2*cpu個數，而我的系統中正好是LOW，CPU正好是32個，那麼就是64個程式了。
可是又是什麼引起rollback呢，並且還要rollback這麼多這麼久？應該是有人做了批次DML，然後rollback了。