问题:
您想找出数据库中最近的重要等待以及负责大多数等待的用户,SQL语句和对象。
解
Oracle为我们提供了V $ACTIVE_SESSION_HISTORY,以获取有关最常见的等待事件以及SQL语句,数据库对象和负责这些等待的用户的信息。
SQL查找等待事件
SELECT event, SUM(wait_time + time_waited) total_wait_time FROM v$active_session_history GROUP BY event ORDER BY total_wait_time DESC;
要找出等待时间最多的用户,我们可以在SQL下面使用。
SELECT s.sid, s.username, SUM(a.wait_time + a.time_waited) total_wait_time FROM v$active_session_history a, v$session s WHERE a.session_id=s.sid GROUP BY s.sid, s.username ORDER BY total_wait_time DESC;
为了找出等待时间最多的对象,我们可以在SQL下面使用。
SELECT a.current_obj#, d.object_name, d.object_type, a.event, SUM(a.wait_time + a.time_waited) total_wait_time FROM v$active_session_history a, dba_objects d WHERE a.current_obj# = d.object_id GROUP BY a.current_obj#, d.object_name, d.object_type, a.event ORDER BY total_wait_time;
最后,我们可以使用以下查询来确定等待最长时间的SQL语句。
SELECT a.user_id, u.username, s.sql_text, SUM(a.wait_time + a.time_waited) total_wait_time FROM v$active_session_history a, v$sqlarea s, dba_users u WHERE a.sql_id = s.sql_id AND a.user_id = u.user_id GROUP BY a.user_id, s.sql_text, u.username;