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丸趣 TV 小编给大家分享一下数据库中如何查看历史会话等待事件对应的 session 信息，希望大家阅读完这篇文章之后都有所收获，下面让我们一起去探讨吧！
此处以 enq: TX – row lock contention 等待时间为例。
如果在此回话发生在 awr 快照信息默认的保存天数以内。
可以通过如下 sql 查询到相关的 session 信息。
select * from DBA_HIST_ACTIVE_SESS_HISTORY where event like %enq: TX – row lock contention%
DBA_HIST_ACTIVE_SESS_HISTORY 中的 blocking_session 字段关联 DBA_HIST_ACTIVE_SESS_HISTORY 中的 session_id 找到对应的 sql_id 从而得到回话信息。
可以通过如下查询直接获取信息：
select t.instance_number,
t.sample_time,
lpad(– , 2 * (level – 1), – ) || t.client_id,
t.session_id,
t.blocking_session,
t.session_serial#,
t.sql_id,
t.event,
t.session_state,
level,
connect_by_isleaf,
connect_by_iscycle
from dba_hist_active_sess_history t
where snap_id between 36878 and 36879
start with blocking_session is not null
and event like enq: TX – row lock contention%
connect by nocycle sample_time = prior sample_time
and session_id = prior blocking_session
and session_serial# = prior blocking_session_serial#
其中 blocking session 为正在阻塞该回话的 session
实战案例：
查看等待事件为行锁的 session
select a.snap_id,
a.sql_id,
a.session_id,
a.session_serial#,
a.blocking_session,
a.blocking_session_serial#,
a.blocking_session_status
from DBA_HIST_ACTIVE_SESS_HISTORY a
where event like %enq: TX – row lock contention%
and snap_id between 20399 and 20400
编写子查询，查看阻塞回话，并统计阻塞次数
select a.blocking_session,
a.blocking_session_serial#,
count(a.blocking_session)
from DBA_HIST_ACTIVE_SESS_HISTORY a
where event like %enq: TX – row lock contention%
and snap_id between 20399 and 20400
group by a.blocking_session, a.blocking_session_serial#
order by 3 desc
查看阻塞回话的 sql_id 和被阻塞的 sql_id，条件为阻塞大于 19 次的
select distinct b.sql_id,c.blocked_sql_id
from DBA_HIST_ACTIVE_SESS_HISTORY b,
(select a.sql_id as blocked_sql_id,
a.blocking_session,
a.blocking_session_serial#,
count(a.blocking_session)
from DBA_HIST_ACTIVE_SESS_HISTORY a
where event like %enq: TX – row lock contention%
and snap_id between 20399 and 20400
group by a.blocking_session, a.blocking_session_serial#,a.sql_id
having count(a.blocking_session) 19
order by 3 desc) c
where b.session_id = c.blocking_session
and b.session_serial# = c.blocking_session_serial#
and b.snap_id between 20399 and 20400
动态性能视图注释：
V$ACTIVE_SESSION_HISTORY displays sampled session activity in the database. It contains snapshots of active database sessions taken once a second. A database session is considered active if it was on the CPU or was waiting for an event that didn t belong to the Idle wait class. Refer to the V$EVENT_NAME view for more information on wait classes.
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