Oracle ASH(Active Session History) ——ashrpt

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。

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。
ASH内存记录数据始终是有限的，为了保存历史数据，ASH写满后会将信息写出到AWR负载库中。

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_hist查询。

ASH报告生成脚本：@?/rdbms/admin/ashrpt.sql


[code][oracle@localhost admin]$ sqlplus / as sysdba

SQL*Plus: Release 11.2.0.1.0 Production on Thu Mar 28 18:03:28 2013

Copyright (c) 1982, 2009, Oracle. All rights reserved.


Connected to:
Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options

SQL> @/oracle/product/database/rdbms/admin/ashrpti.sql

Specify the Report Type
~~~~~~~~~~~~~~~~~~~~~~~
Enter 'html' for an HTML report, or 'text' for plain text
Defaults to 'html'
Enter value for report_type:

Type Specified: html


Instances in this Workload Repository schema
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

DB Id Inst Num DB Name Instance Host
------------ -------- ------------ ------------ ------------
1972453558 1 ECARD ecard1 ecarddb1
* 2205835418 1 ORASQL orasql localhost.lo
caldomain

* 2205835418 1 ORASQL orasql localhost
1972453558 2 ECARD ecard2 ecarddb2

Defaults to current database
Enter value for dbid: 1972453558

Using database id: 1972453558

Enter instance numbers. Enter 'ALL' for all instances in a
RAC cluster or explicitly specify list of instances (e.g., 1,2,3).
Defaults to current instance.
Enter value for inst_num: 1

Using instance number(s): 1





ASH Samples in this Workload Repository schema
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Oldest ASH sample available: 13-Mar-13 22:59:36 [ 21304 mins in the past]
Latest ASH sample available: 21-Mar-13 10:29:38 [ 10534 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: 03/15/13 08:30:00
Report begin time specified: 03/15/13 08:30:00

Enter duration in minutes starting from begin time:
Defaults to SYSDATE - begin_time
Press Enter to analyze till current time
Enter value for duration: 180
Report duration specified: 180

Using 15-Mar-13 08:30:00 as report begin time
Using 15-Mar-13 11:30:00 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:
Enter value for slot_width:
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:
Enter value for target_session_id:
SESSION report target specified:


Specify SQL_ID (eg: from V$SQL.SQL_ID) report target:
Defaults to NULL: (% and _ wildcards allowed)
Enter value for target_sql_id:
SQL report target specified:


Specify WAIT_CLASS name (eg: from V$EVENT_NAME.WAIT_CLASS) report target:
[Enter 'CPU' to investigate CPU usage]
Defaults to NULL: (% and _ wildcards allowed)
Enter value for target_wait_class:
WAIT_CLASS report target specified:


Specify SERVICE_HASH (eg: from V$ACTIVE_SERVICES.NAME_HASH) report target:
Defaults to NULL:
Enter value for target_service_hash:
SERVICE report target specified:


Specify MODULE name (eg: from V$SESSION.MODULE) report target:
Defaults to NULL: (% and _ wildcards allowed)
Enter value for target_module_name:
MODULE report target specified:


Specify ACTION name (eg: from V$SESSION.ACTION) report target:
Defaults to NULL: (% and _ wildcards allowed)
Enter value for target_action_name:
ACTION report target specified:


Specify CLIENT_ID (eg: from V$SESSION.CLIENT_IDENTIFIER) report target:
Defaults to NULL: (% and _ wildcards allowed)
Enter value for target_client_id:
CLIENT_ID report target specified:


Specify PLSQL_ENTRY name (eg: "SYS.DBMS_LOB.*") report target:
Defaults to NULL: (% and _ wildcards allowed)
Enter value for target_plsql_entry:
PLSQL_ENTRY report target specified:

Specify the Report Name
~~~~~~~~~~~~~~~~~~~~~~~
The default report file name is ashrpt_1_0315_1130.html. To use this name,
press <return> to continue, otherwise enter an alternative.
Enter value for report_name: /oracle/ash_0315.html

Using the report name /oracle/ash_0315.html

Summary of All User Input
-------------------------
Format : HTML
DB Id : 1972453558
Inst num : 1
Begin time : 15-Mar-13 08:30:00
End time : 15-Mar-13 11:30:00
Slot width : Default
Report targets : 0
Report name : /oracle/ash_0315.html[/code]