应用环境：
操作系统： RedHat EL55
Oracle： Oracle 10gR2
案例场景：
SCOTT用户做事务处理，事务已经完成！
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16
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42
:
14
SYS@ prod>conn scott/tiger
Connected.
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42
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SCOTT@ prod>begin
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2
for
i in
1
..
1000000
loop
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3
execute immediate
'insert into t1 values ('
||i||
')'
;
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end loop;
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end;
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6
/
PL/SQL procedure successfully completed.
Elapsed:
00
:
08
:
35.77
16
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51
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14
SCOTT@ prod>commit;
Commit complete.
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生成ASH报告：
16:55:43 SYS@ prod>@?/rdbms/admin/ashrpt
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Current Instance
~~~~~~~~~~~~~~~~
DB Id DB Name Inst Num Instance
----------- ------------ -------- ------------
199802235
PROD
1
prod
Elapsed:
00
:
00
:
00.07
Specify the Report Type
~~~~~~~~~~~~~~~~~~~~~~~
Enter
'html'
for
an HTML report,
or
'text'
for
plain text
Defaults to
'html'
Enter value
for
report_type: html
Type Specified: html
Instances
in
this
Workload Repository schema
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
DB Id Inst Num DB Name Instance Host
------------ -------- ------------ ------------ ------------
*
199802235
1
PROD prod rh55
Defaults to current database
Using database id:
199802235
Defaults to current instance
Using instance number:
1
ASH Samples
in
this
Workload Repository schema
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Oldest ASH sample available:
15
-Aug
-14
11
:
55
:
37
[
4625
mins
in
the past]
Latest ASH sample available:
18
-Aug
-14
17
:
00
:
17
[
1
mins
in
the past]
Specify the timeframe to generate the ASH report
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Enter begin time
for
report:
-- Valid input formats:
-- To specify absolute begin time:
-- [MM/DD[/YY]] HH24:MI[:SS]
-- Examples:
02
/
23
/
03
14
:
30
:
15
--
02
/
23
14
:
30
:
15
--
14
:
30
:
15
--
14
:
30
-- To specify relative begin time: (start
with
'-'
sign)
-- -[HH24:]MI
-- Examples:
-1
:
15
(SYSDATE -
1
Hr
15
Mins)
--
-25
(SYSDATE -
25
Mins)
Defaults to
-15
mins
Enter value
for
begin_time:
-10
Enter duration
in
minutes starting
from
begin time:
Defaults to SYSDATE - begin_time
Press Enter to analyze till current time
Enter value
for
duration:
Report duration specified:
Using
18
-Aug
-14
16
:
51
:
39
as
report begin time
Using
18
-Aug
-14
17
:
01
:
40
as
report end time
Specify Slot Width (using ashrpti.sql)
for
'Activity Over Time'
section
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-- Explanation:
-- In the
'Activity Over Time'
section of the ASH report,
-- the analysis period is divided
into
smaller slots
--
and
top wait events are reported
in
each of those slots.
-- Default:
-- The analysis period will be automatically split upto
10
slots
-- complying to a minimum slot width of
--
1
minute,
if
the source is V$ACTIVE_SESSION_HISTORY
or
--
5
minutes,
if
the source is DBA_HIST_ACTIVE_SESS_HISTORY.
Specify Slot Width
in
seconds to use
in
the
'Activity Over Time'
section:
Defaults to a value
as
explained above:
Slot Width specified:
Specify Report Targets (using ashrpti.sql) to generate the ASH report
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-- Explanation:
-- ASH Report can accept
"Report Targets"
,
-- like a particular SQL statement,
or
a particular SESSION,
-- to generate the report
on
. If one
or
more report targets are
-- specified,
then
the data used to generate the report will only be
-- the ASH samples that pertain to ALL the specified report targets.
-- Default:
-- If none of the report targets are specified,
--
then
the target defaults to all activity
in
the database instance.
Specify SESSION_ID (eg:
from
V$SESSION.SID) report target:
Defaults to NULL:
SESSION report target specified:
Specify SQL_ID (eg:
from
V$SQL.SQL_ID) report target:
Defaults to NULL: (%
and
_ wildcards allowed)
SQL report target specified:
Specify WATI_CLASS name (eg:
from
V$EVENT_NAME.WAIT_CLASS) report target:
[Enter
'CPU'
to investigate CPU usage]
Defaults to NULL: (%
and
_ wildcards allowed)
WAIT_CLASS report target specified:
Specify SERVICE_HASH (eg:
from
V$ACTIVE_SERVICES.NAME_HASH) report target:
Defaults to NULL:
SERVICE report target specified:
Specify MODULE name (eg:
from
V$SESSION.MODULE) report target:
Defaults to NULL: (%
and
_ wildcards allowed)
MODULE report target specified:
Specify ACTION name (eg:
from
V$SESSION.ACTION) report target:
Defaults to NULL: (%
and
_ wildcards allowed)
ACTION report target specified:
Specify CLIENT_ID (eg:
from
V$SESSION.CLIENT_IDENTIFIER) report target:
Defaults to NULL: (%
and
_ wildcards allowed)
CLIENT_ID report target specified:
Specify the Report Name
~~~~~~~~~~~~~~~~~~~~~~~
The default report file name is ashrpt_1_0818_1704.html. To use
this
name,
press <
return
> to
continue
, otherwise enter an alternative.
Enter value
for
report_name: ash3.html
|
查看生成报告
通过html方式查看ASH报告：
基本信息
TOP事件：User TOP EVENTS
TOP SQL
TOP SESSION
TOP OBJECTS
ASH 说明
ASH以V$SESSION为基础，每秒采样一次，记录活动会话等待的事件。不活动的会话不会采样，采样工作由新引入的后台进程MMNL来完成。
ASH buffers 的最小值为1MB,最大值不超过30MB。内存中记录数据。期望值是记录一小时的内容。
ASH内存分配：
SQL> select * from v$sgastat where name like '%ASH%';
POOL NAME BYTES
------------ -------------------------- ----------
shared pool ASH buffers 8388608
ASH报告生成脚本：@?/rdbms/admin/ashrpt.sql
ASH内存记录数据始终是有限的，为了保存历史数据，引入了自动负载信息库(Automatic Workload Repository ,AWR) 由后台进程MMON完成。ASH信息同样被采集写出到AWR负载库中。由于内存不是足够的，所以MMNL进程在ASH写满后会将信息写出到AWR负载库中。ASH全部写出是不可接受的，所以一般只写入收集的10%的数据量，而且使用direct-path insert完成，尽量减少日志的生成，从而最小化数据库性能影响。
内存中的ASH 信息可以通过V$ACTIVE_SESSION_HISTORY查询，而写出到AWR负载库的ASH信息，可以通过AWR的基础表wrh$_active_session_history查询，wrh$_active_session_history是一个分区表，Oracle会自动进行数据清理。
一般来说，我们在监控数据库时，如果是当前正在发生的问题，我们可以通过v$session+v$sqlarea来找出性能最差的SQL语句。如果在一个小时以内发生的我们可以通过生成ASH报告来找出SQL。如果是1小时以上或几天我们可以通过AWR报告来找出几小时，几天以来最影响系统的SQL语句。ADDM报告基于AWR库，默认可以保存30天的ADDM报告。
相关查询试图：
v$session (当前正在发生)
v$session_wait (当前正在发生)
v$session_wait_history (会话最近的10次等待事件)
v$active_session_history (内存中的ASH采集信息，理论为1小时)
wrh$_active_session_history (写入AWR库中的ASH信息，理论为1小时以上)
dba_hist_active_sess_history (根据wrh$_active_session_history生成的视图)
三. ASH 报告生成示例
ASH组件以v$active_session_history视图为基础，生成ASH报表，ASH报表与statspack类似，可以提供以下信息：
Top User Events
Top Background Events
Top Event P1/P2/P3 Values
Top Service/Module
Top Client IDs
Top SQL Command Types
Top SQL using literals
Top Blocking Sessions
Top DB Objects
Top DB Files
Top Latches
Activity Over Time
报表间隔时间可以精确到分钟，因而ASH可以提供比STATSPACK或AWR更详细的关于历史会话的信息，可以作为statspack或awr的补充。ASH报告通过@$ORACLE_HOME/rdbms/admin/ashrpt.sql脚本生成，包括hmtl和text两种格式。
