ASH分析

ASH分析常规流程和SQL语句

step1 验证导出的ASH时间范围

select 
 t.dbid, t.instance_number, min(sample_time), max(sample_time), count(*) session_count
  from DBA_HIST_ACTIVE_SESS_HISTORY t
 group by t.dbid, t.instance_number
 order by dbid, instance_number;

step2 确认问题发生的精确时间范围

select 
 dbid, instance_number, sample_id, sample_time, count(*) session_count
  from DBA_HIST_ACTIVE_SESS_HISTORY t
 group by dbid, instance_number, sample_id, sample_time
 order by dbid, instance_number, sample_time;

step3 确定每个采样点的top n event

select t.dbid,
       t.sample_id,
       t.sample_time,
       t.instance_number,
       t.event,
       t.session_state,
       t.c session_count
  from (select t.*,
               rank() over(partition by dbid, instance_number, sample_time order by c desc) r
          from (select 
                 t.*,
                 count(*) over(partition by dbid, instance_number, sample_time, event) c,
                 row_number() over(partition by dbid, instance_number, sample_time, event order by 1) r1
                  from DBA_HIST_ACTIVE_SESS_HISTORY t
                where sample_time >
                    to_timestamp('2022-09-27 07:00:00',
                                 'yyyy-mm-dd hh24:mi:ss')
                and sample_time <
                    to_timestamp('2022-09-27 08:00:00',
                                 'yyyy-mm-dd hh24:mi:ss')
                ) t
         where r1 = 1) t
 where r < 3
 order by dbid, instance_number, sample_time, r;

step4 观察每个采样点的等待链

`select 
 level                     lv,
 connect_by_isleaf         isleaf,
 connect_by_iscycle        iscycle,
 t.dbid,
 t.sample_id,
 t.sample_time,
 t.instance_number,
 t.session_id,
 t.sql_id,
 t.session_type,
 t.event,
 t.session_state,
 t.blocking_inst_id,
 t.blocking_session,
 t.blocking_session_status
  from DBA_HIST_ACTIVE_SESS_HISTORY t
where sample_time >
                    to_timestamp('2022-09-27 07:20:00',
                                 'yyyy-mm-dd hh24:mi:ss')
                and sample_time <
                    to_timestamp('2022-09-27 07:40:00',
                                 'yyyy-mm-dd hh24:mi:ss')
 start with blocking_session is not null
connect by nocycle
 prior dbid = dbid
       and prior sample_time = sample_time
       and prior blocking_inst_id = instance_number
       and prior blocking_session = session_id
       and prior blocking_session_serial# = session_serial#
 order siblings by dbid, sample_time;`

step5 基于第4步的原理来找出每个采样点的最终top holder

select t.lv,
       t.iscycle,
       t.dbid,
       t.sample_id,
       t.sample_time,
       t.instance_number,
       t.session_id,
       t.sql_id,
       t.session_type,
       t.event,
       t.seq#,
       t.session_state,
       t.blocking_inst_id,
       t.blocking_session,
       t.blocking_session_status,
       t.c blocking_session_count
  from (select t.*,
               row_number() over(partition by dbid, instance_number, sample_time order by c desc) r
          from (select t.*,
                       count(*) over(partition by dbid, instance_number, sample_time, session_id) c,
                       row_number() over(partition by dbid, instance_number, sample_time, session_id order by 1) r1
                  from (select 
                         level              lv,
                         connect_by_isleaf  isleaf,
                         connect_by_iscycle iscycle,
                         t.*
                          from DBA_HIST_ACTIVE_SESS_HISTORY t
                        where sample_time >
                    to_timestamp('2022-09-27 07:30:00',
                                 'yyyy-mm-dd hh24:mi:ss')
                and sample_time <
                    to_timestamp('2022-09-27 07:40:00',
                                 'yyyy-mm-dd hh24:mi:ss')
                         start with blocking_session is not null
                        connect by nocycle
                         prior dbid = dbid
                               and prior sample_time = sample_time
                               and prior blocking_inst_id = instance_number
                               and prior blocking_session = session_id
                               and prior
                                    blocking_session_serial# = session_serial#) t
                 where t.isleaf = 1) t
         where r1 = 1) t
 where r < 3
 order by dbid, sample_time, r;