使用ASH监控历史会话,找出坏SQL-优快云博客

本文介绍了一种使用Oracle数据库内置视图v$active_session_history来监控并诊断系统中等待事件的方法。通过SQL查询，可以获取历史会话的等待事件详情，包括事件类型、发生次数及总等待时间，并进一步定位到具体的SQL语句。

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使用如下脚本可以监控历史会话经历过哪些等待事件，并且按照等待次数降序排列

select session_id,event,count(*),sum(time_waited) from v$active_session_history where session_state='WAITING'
and time_waited>0 and sample_time>=(sysdate-&howlongago/(24*60))
group by session_id,event order by 3 desc;
例子:

SQL> select session_id,event,count(*),sum(time_waited) from v$active_session_history where session_state='WAITING'
2 and time_waited>0 and sample_time>=(sysdate-&howlongago/(24*60))
3 group by session_id,event order by 3 desc;
输入 howlongago 的值: 5
原值 2: and time_waited>0 and sample_time>=(sysdate-&howlongago/(24*60))
新值 2: and time_waited>0 and sample_time>=(sysdate-5/(24*60))

SESSION_ID EVENT COUNT(*) SUM(TIME_WAITED)
---------- ------------------------------ ---------- ----------------
150 direct path write temp 3 20825
165 control file sequential read 2 21520
150 direct path read temp 2 38545

然后通过如下语句查询出引起该等待事件的sql_id

select event, session_id,sql_id, p1,p2,p3 from v$active_session_history where sample_time>=(sysdate-&howlongago/(24*60)) and session_id=&sid;

SQL> select event, session_id,sql_id, p1,p2,p3 from v$active_session_history where sample_time>=(sysdate-&howlongago/(24*60)) and session_id=&sid;
输入 howlongago 的值: 8
输入 sid 的值: 150
原值 1: select event, session_id,sql_id, p1,p2,p3 from v$active_session_history where sample_time>=(sysdate-&howlongago/(24*60)) and session_id=&sid
新值 1: select event, session_id,sql_id, p1,p2,p3 from v$active_session_history where sample_time>=(sysdate-8/(24*60)) and session_id=150

EVENT SESSION_ID SQL_ID P1 P2
------------------------------ ---------- ------------- ---------- ----------
P3
----------
direct path read temp 150 fqu3bkz2q6j26 201 58665
1

150 fqu3bkz2q6j26 1111838976 1
0

direct path read temp 150 fqu3bkz2q6j26 201 45897
1

EVENT SESSION_ID SQL_ID P1 P2
------------------------------ ---------- ------------- ---------- ----------
P3
----------
direct path read temp 150 fqu3bkz2q6j26 201 47753
1

再通过如下语句找到引起该等待事件的SQL

select sql_text from v$sqlarea where sql_id='&sql_id';

SQL> select sql_text from v$sqlarea where sql_id='&sql_id';
输入 sql_id 的值: fqu3bkz2q6j26
原值 1: select sql_text from v$sqlarea where sql_id='&sql_id'
新值 1: select sql_text from v$sqlarea where sql_id='fqu3bkz2q6j26'

SQL_TEXT
--------------------------------------------------------------------------------
select a.* from dict a,dict b order by 1