Oracle Wait Events:checkpoint completed

今天帮用户恢复数据库，在关闭数据库时发现如下一个显著的等待事件：

WAIT #1: nam='checkpoint completed' ela= 4892320 p1=0 p2=0 p3=0
WAIT #1: nam='checkpoint completed' ela= 4892538 p1=0 p2=0 p3=0
WAIT #1: nam='checkpoint completed' ela= 4892539 p1=0 p2=0 p3=0
WAIT #1: nam='checkpoint completed' ela= 4892555 p1=0 p2=0 p3=0
WAIT #1: nam='checkpoint completed' ela= 4892541 p1=0 p2=0 p3=0
WAIT #1: nam='checkpoint completed' ela= 4892546 p1=0 p2=0 p3=0
WAIT #1: nam='checkpoint completed' ela= 4892549 p1=0 p2=0 p3=0
WAIT #1: nam='checkpoint completed' ela= 4892495 p1=0 p2=0 p3=0
WAIT #1: nam='checkpoint completed' ela= 4892542 p1=0 p2=0 p3=0
WAIT #1: nam='checkpoint completed' ela= 4892535 p1=0 p2=0 p3=0
WAIT #1: nam='checkpoint completed' ela= 1429367 p1=0 p2=0 p3=0

数据库可能在这个事件上花费大量的等待时间，这个事件没有参数表达：

SQL> SELECT NAME, parameter1, parameter2, parameter3
  2    FROM v$event_name
  3  WHERE NAME = 'checkpoint completed';

NAME                PARAMETER1 PARAMETER2 PARAMETER3
-------------------- ---------- ---------- ----------
checkpoint completed

文档的解释如下：

checkpoint completed
A session waits for a checkpoint to complete.
This could happen, for example, during a close database or a local checkpoint.

Wait Time: 5 seconds
Parameters: None

也就是说，会话在等待检查点的完成，在数据库关闭、本地检查点发生时可能见到。