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我们知道，Oracle中的10203事件可以用来跟踪数据库的块清除（cleanout）操作，我们从事件列表中，可以知道该时间的含义为：“block cleanout”。
10203事件需要在系统级设置，重启后即可生效：
SQL> alter system set event="10203 trace name context forever" scope=spfile;
System altered.
SQL> shutdown immediate;
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup
ORACLE instance started.Total System Global Area 126948772 bytes
Fixed Size 452004 bytes
Variable Size 92274688 bytes
Database Buffers 33554432 bytes
Redo Buffers 667648 bytes
Database mounted.
Database opened.SQL> show parameter event
NAME TYPE VALUE
------------------------------------ ----------- --------------------------------
event string 10203 trace name context forever
注释：在跟踪文件中，你现在即可以发现以下的block cleanout信息：
Begin cleaning out block ...
Found all committed transactions
Block cleanout record, scn: 0xffff.ffffffff ver: 0x01 opt: 0x02, entries follow...
itli: 1 flg: 2 scn: 0x0819.0045cd54
Block cleanout under the cache...
Block cleanout record, scn: 0x0819.0045cea1 ver: 0x01 opt: 0x02, entries follow...
itli: 1 flg: 2 scn: 0x0819.0045cd54
... clean out dump complete.
