Oracle的10203事件可以用来跟踪数据库的块清除（cleanout）操作,从事件列表中，我们可以知道该时间的含义为：block cleanout 。

该事件需要在系统级设置，重启数据库后生效：

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
 
在跟踪文件中，我们可以发现类似如下的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.