1.查询以往的session历史信息

select * from v$active_session_history where session_id=12 and session_serial#=703;

2.查询ash使用的空间：

select * from v$sgastat where name like 'ASH%' ;

3.确认目前ash相关设置，如ash是否启用，间隔多久采样数据等

select a.ksppinm name, b.ksppstvl value, a.ksppdesc description

from x$ksppi a, x$ksppcv b

where a.indx = b.indx

and a.ksppinm like '_ash%' ;

4.查询确认目前ash最旧的采样时间：

select to_char(min(sample_time),'yyyy/mm/dd hh24:mi:ss') "Sample Time" from v$active_session_history ;

5.查询最近10分钟内最耗费cpu的sql语句：

select a.sql_id, a.sess_count, a.cpu_load, b.sql_text

from (select sql_id,

count(*) sess_count,

round(count(*) / sum(count(*)) over(), 2) cpu_load

from v$active_session_history

where sample_time > sysdate - 1 / (24 * 6)

and session_type <> 'BACKGROUND'

and session_state = 'ON CPU'

group by sql_id

order by count(*) desc) a,

v$sqlarea b

where a.sql_id = b.sql_id ;

6.查询最近10分钟内最耗费io的sql语句：

select a.sql_id, a.sess_count, a.sess_count, b.sql_text

from (select ash.sql_id, count(*) sess_count

from v$active_session_history ash, v$event_name evt

where ash.sample_time > sysdate - 1 / (24 * 6)

and ash.session_state = 'WAITING'

and ash.event_id = evt.event_id

and evt.wait_class = 'User I/O'

group by ash.sql_id

order by count(*) desc) a,

v$sqlarea b

where a.sql_id = b.sql_id;

7.查询最近10分钟内最耗费系统资源的sql语句：

select a.sql_id, a.cpu, a.wait, a.io, a.total, b.sql_text

from (select ash.sql_id,

sum(decode(ash.session_state, 'ON CPU', 1, 0)) "CPU",

sum(decode(ash.session_state, 'WAITING', 1, 0)) -

sum(decode(ash.session_state,'WAITING',decode(en.wait_class, 'USER I/O', 1, 0), 0)) "WAIT",

sum(decode(ash.session_state,'WAITING',decode(en.wait_class, 'USER I/O', 1, 0), 0)) "IO",

sum(decode(ash.session_state, 'ON CPU', 1, 1)) "TOTAL"

from v$active_session_history ash, v$event_name en

where sql_id is not null

and en.event# = ash.event#

and ash.sample_time > sysdate - 1 / (24 * 6)

group by ash.sql_id

order by sum(decode(ash.session_state, 'ON CPU', 1, 1)) desc) a,

v$sqlarea b

where a.sql_id = b.sql_id;

8.查询最近10分钟内最耗费系统资源的数据库会话：

select a.sid,a.serial#,b.username,a.user_id,a.program,a.cpu,a.waiting,a.io,a.total

from (select ash.session_id sid,

ash.session_serial# serial#,

ash.user_id,

ash.program,

sum(decode(ash.session_state, 'ON CPU', 1, 0)) "CPU",

sum(decode(ash.session_state, 'WAITING', 1, 0)) -

sum(decode(ash.session_state,'WAITING',decode(en.wait_class, 'USER I/O', 1, 0), 0)) "WAITING",

sum(decode(ash.session_state,'WAITING',decode(en.wait_class, 'USER I/O', 1, 0), 0)) "IO",

sum(decode(ash.session_state, 'ON CPU', 1, 1)) "TOTAL"

from v$active_session_history ash, v$event_name en

where sql_id is not null

and en.event# = ash.event#

and ash.sample_time > sysdate - 1 / (24 * 6)

group by ash.session_id,ash.user_id,ash.session_serial#,ash.program

order by sum(decode(ash.session_state, 'ON CPU', 1, 1)) desc) a,

v$session b

where a.sid = b.sid;

9.查询当前用户会话是在等待哪一个会话：

select distinct a.session_id,

a.session_serial#,

a.sql_id,

a.session_state,

a.session_type,

a.blocking_session,

a.blocking_session_serial#,

a.blocking_session_status,

a.event,

a.sql_id

from v$active_session_history a, v$session s

where a.blocking_session is not null

and a.blocking_session = s.sid

and a.blocking_session_serial# = s.serial#

and s.sql_id is not null;

10.

Oracle11g停用自动分析的方式：

exec dbms_auto_task_admin.disable(client_name=>'auto optimizer stats collection',operation=>null,window_name=>null) ;

Oracle11g启用自动分析的方式：

exec dbms_auto_task_admin.enable(client_name=>'auto optimizer stats collection',operation=>null,window_name=>null) ;

查询旧的统计数据保留的天数：

select dbms_stats.get_stats_history_retention from dual ;

修改统计数据保留的天数：

exec dbms_stats.alter_stats_history_retention(60) ;

查询目前最早的统计数据时间：

select dbms_stats.get_stats_history_availability from dual ;

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