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  • 查看历史会话等待事件对应的session信息

    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).

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  • 原文地址:https://www.cnblogs.com/kawashibara/p/10473867.html
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