SQL> alter system set log_checkpoints_to_alert=true;

--启用在alert中开启检查点事件记录功能

System altered.

-bash-3.2$ tail -f alert_orcl.log --查看alert
Wed Aug 18 13:53:43 2010
Completed: alter tablespace users end backup
Wed Aug 18 15:52:26 2010
create tablespace test datafile '/oracle/oradata/orcl/test01.dbf' size 10m
Wed Aug 18 15:52:26 2010
Completed: create tablespace test datafile '/oracle/oradata/orcl/test01.dbf' size 10m
Wed Aug 18 16:27:59 2010
ALTER SYSTEM: Flushing buffer cache
Wed Aug 18 16:47:43 2010
ALTER SYSTEM SET log_checkpoints_to_alert=TRUE SCOPE=BOTH;

--这是执行alter system switch logfile发生的检查事件
Wed Aug 18 16:48:11 2010 --发生时间

--发生检查点的rba及scn
Beginning log switch checkpoint up to RBA [0xf.2.10], SCN: 753891
Thread 1 advanced to log sequence 15
  Current log# 2 seq# 15 mem# 0: /oracle/oradata/orcl/redo02.log

--又执行一次alter system switch logfile
Wed Aug 18 16:48:39 2010
Beginning log switch checkpoint up to RBA [0x10.2.10], SCN: 753901
Thread 1 advanced to log sequence 16
  Current log# 3 seq# 16 mem# 0: /oracle/oradata/orcl/redo03.log

--来了一次完全检查点

---alter system checkpoint
Wed Aug 18 16:49:30 2010
Beginning global checkpoint up to RBA [0x10.2.10], SCN: 753918

--这下同时把上面的检查点工作完成了
Completed checkpoint up to RBA [0x10.2.10], SCN: 753918
Completed checkpoint up to RBA [0x10.2.10], SCN: 753901
Completed checkpoint up to RBA [0xf.2.10], SCN: 753891

说明：

 检查点是一种事件，它的触发（发生）到完成检查点，不是同步的，是需要一定的时间

所以这个调优很重要了