查看历史会话等待事件对应的session信息

Posted 2020-10-14 ClarkYu

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