此处以enq: TX - row lock contention等待时间为例。
查看snap_id对应时间
select to_char(s.startup_time,‘dd Mon "at" HH24:mi:ss‘) instart_fmt
, di.instance_name inst_name
, di.db_name db_name
, s.snap_id snap_id
, to_char(s.end_interval_time,‘dd Mon YYYY HH24:mi‘) snapdat
, s.snap_level lvl
from dba_hist_snapshot s
, dba_hist_database_instance di
where di.dbid = s.dbid
and di.instance_number = s.instance_number
and di.startup_time = s.startup_time
order by db_name, instance_name, snap_id;
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%‘
select * from dba_hist_active_sess_history WHERE event like ‘enq: TX - row lock contention%‘ order by SAMPLE_TIME DESC
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.
这个视图三思老师的博客里将的比较清楚：
http://blog.itpub.net/7607759/viewspace-617178
This view contains one row for each active session per sample and returns the latest session sample rows first. A majority of the columns describing the session in the active session history are present in the V$SESSION view.
DBA_HIST_ACTIVE_SESS_HISTORY displays the history of the contents of the in-memory active session history of recent system activity. This view contains snapshots of V$ACTIVE_SESSION_HISTORY. See "V$ACTIVE_SESSION_HISTORY" for further interpretation details for many of these columns (except SNAP_ID, DBID, and INSTANCE_NUMBER).
原文：https://www.cnblogs.com/kawashibara/p/10473867.html