通过案例学习调优之--Oracle ASH

通过案例学习调优之--Oracle ASH
应用环境：操作系统： RedHat EL55Oracle： Oracle 10gR2
案例场景：
SCOTT用户做事务处理，事务已经完成！

16:42:14 SYS@ prod>conn scott/tiger
Connected.
16:42:20 SCOTT@ prod>begin
16:42:23   2  for i in 1..1000000 loop
16:42:27   3  execute immediate 'insert into t1 values ('||i||')';
16:42:32   4  end loop;
16:42:36   5  end;
16:42:38   6  /
PL/SQL procedure successfully completed.
Elapsed: 00:08:35.77
16:51:14 SCOTT@ prod>commit;
Commit complete.

生成ASH报告：

16:55:43 SYS@ prod>@?/rdbms/admin/ashrpt

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 EventsTop Background EventsTop Event P1/P2/P3 ValuesTop Service/ModuleTop Client IDsTop SQL Command TypesTop SQL using literalsTop Blocking SessionsTop DB ObjectsTop DB FilesTop LatchesActivity 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。

本文出自 “天涯客的blog” 博客，请务必保留此出处http://tiany.blog.51cto.com/513694/1541673