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通过案例学习调优之--Oracle ASH

发表于：2024-11-23 作者：千家信息网编辑

千家信息网最后更新 2024年11月23日，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

千家信息网最后更新 2024年11月23日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 EL55

Oracle： 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/tigerConnected.16:42:20 SCOTT@ prod>begin16:42:23   2  for i in 1..1000000 loop16:42:27   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: 00:08:35.7716:51:14 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 prodElapsed: 00:00:00.07Specify the Report Type~~~~~~~~~~~~~~~~~~~~~~~Enter 'html' for an HTML report, or 'text' for plain textDefaults to 'html'Enter value for report_type: htmlType Specified:  htmlInstances in this Workload Repository schema~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~   DB Id     Inst Num DB Name      Instance     Host------------ -------- ------------ ------------ ------------* 199802235         1 PROD         prod         rh65Defaults to current databaseUsing database id: 199802235Defaults to current instanceUsing instance number: 1ASH 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 minsEnter value for begin_time: -10Enter duration in minutes starting from begin time:Defaults to SYSDATE - begin_timePress Enter to analyze till current timeEnter value for duration: Report duration specified:Using 18-Aug-14 16:51:39 as report begin timeUsing 18-Aug-14 17:01:40 as report end timeSpecify 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  to continue, otherwise enter an alternative.Enter value for report_name: ash4.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