我寫的SQL調優專欄：https://blog.csdn.net/u014427391/article/category/8679315
對於局部的，比如某個頁面列表sql，我們可以使用Oracle的執行計划進行sql調優，但是對於整個系統來說，你可以知道哪些sql比較耗時？當然可以通過查Oracle的共享池得到，不過Oracle系統本身就提供了幾種性能分析報告，比如AWR、ASH、ADDM等等報告，本博客介紹一下ASH性能分析報告
ASH即活動會話歷史，Active Session History，ASH以V$SESSION為基礎，每秒采樣一次，記錄活動會話等待的事件。不活動的會話不會采樣， 采樣工作由新引入的后台進程MMNL完成。
v$active_session_history視圖提供了在實例級別抽取會話活動信息。活動會話每分鍾會被抽樣一次且被存儲在sga中的循環緩沖區中。任何被連接到數據庫且正等待一個不屬於空閑等待時間的會話會被考慮是一個活動的會話。每個會話抽樣都是一組行數據且通過v$active_session_history視圖來返回每個被抽樣活動會話的行數據，返回最新被抽樣會話的第一行數據。
一、ASH報告生成
繼上一篇AWR方面的博客之后，https://smilenicky.blog.csdn.net/article/details/89414432，我再寫一篇ASH方面的博客：
1.1 工具選擇
對於Oracle數據庫可以使用sqlplus或者plsql developer客戶端軟件
sqlplus 使用
可以使用sqlplus工具登錄
進入數據庫
sqlplus / as sysdba
查看用戶
show parameter db_name
用登錄之后才可以使用
plsql developer使用
plsql developer也可以使用，登錄之后，選擇文件(File)->新建(New)->命令窗口(Command Window)
1.2 自動創建快照
開始壓測后執行
exec DBMS_WORKLOAD_REPOSITORY.CREATE_SNAPSHOT ();
可以通過dba_hist_wr_control查看當前的配置情況，當前awr為每1小時做一次數據快照，保留時間為8天。
select * from dba_hist_wr_control;
修改配置，每隔30分鍾收集一次，保存1天
execute dbms_workload_repository.modify_snapshot_settings(interval=>30,retention=>14000);
關閉自動收集
SQL>exec dbms_workload_repository.modify_snapshot_settings (interval=>0,retention=>24*60);
1.3 手工創建快照
除了自動創建快照，也可以手工創建快照
select dbms_workload_repository.create_snapshot() from dual;
1.4 ASH報告生成
對於sqlplus客戶端的可以使用
@?/rdbms/admin/ashrpt.sql
對於plsql客戶端，我用絕對路徑去執行，@?的命令找不到文件
這個要根據自己的Oracle安裝路徑去修改，例如：
@D:/oracle/product/11.1.0/db_1/RDBMS/ADMIN/ashrpt.sql
（1）日志報告類型
Enter value for report_type: text
選擇生成的ASH 報告類型，是text 還是html，一般選擇html
（2）日志報告起始時間
Enter value for begin_time: 04/18/1920:00:00
輸入ASH 開始的時間，時間格式上面的示例有說明，比如我這里是2019年4月18日晚上20:00:00開始。
（3）日志報告結束時間
Enter value for duration:15
輸入ASH 結束時間，默認是SYSDATE - begin_time，一般輸入，一般默認是秒或者分組，拿出15分組的ash分析日志來。
(4) ASH報告名稱
Enter value of report name:ash20190420
輸入ASH報告名稱，可以隨意填，非生產，報告名稱，打印的日志后面可以找到報告存放路徑，比如：
D:\oracle\product\11.2.0\dbhome_1\RDBMS\ADMIN\ash.html
SQL> @D:/oracle/product/11.1.0/db_1/RDBMS/ADMIN/ashrpt.sql
Current Instance
~~~~~~~~~~~~~~~~
DBID DB_NAME INST_ INST_NAME
---------- ------------ ----- ------------
1525762377 ORCL 1 orcl
Specify the Report Type
~~~~~~~~~~~~~~~~~~~~~~~
Enter 'html' for an HTML report, or 'text' for plain text
Defaults to 'html'
Type Specified: html
Instances in this Workload Repository schema
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
DBBID INSTT DBB_NAME INSTT_NAME HOST
------------ ----- ------------ ------------ ------------
* 1525762377 1 ORCL orcl PC-201508171
906
Defaults to current database
Using database id: 1525762377
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.
Using instance number(s): 1
PL/SQL procedure successfully completed
...
0
PL/SQL procedure successfully completed
...
18-Apr-19 22:05:54
ASH Samples in this Workload Repository schema
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Oldest ASH sample available: 09-Apr-19 22:00:36 [ 12968 mins in the past] Latest ASH sample available: 18-Apr-19 22:05:54 [ 3 mins in the past]
...
18-Apr-19 22:05:54
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
Report begin time specified: 04/18/1920:00:00
PL/SQL procedure successfully completed
18-Apr-20 00:00:00
Enter duration in minutes starting from begin time:
Defaults to SYSDATE - begin_time
Press Enter to analyze till current time
Report duration specified: 7200
PL/SQL procedure successfully completed
...
23-Apr-20 00:00:00
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 WAIT_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 PLSQL_ENTRY name (eg: "SYS.DBMS_LOB.*") report target:
Defaults to NULL: (% and _ wildcards allowed)
PLSQL_ENTRY report target specified:
Specify the Report Name
~~~~~~~~~~~~~~~~~~~~~~~
The default report file name is ashrpt_1_0423_0000.html. To use this name,
press <return> to continue, otherwise enter an alternative.
Using the report name ash.html
Summary of All User Input ------------------------- Format : HTML DB Id : 1525762377 Inst num : 1 Begin time : 18-Apr-20 00:00:00 End time : 23-Apr-20 00:00:00 Slot width : Default Report targets : 0 Report name : ash.html
...
23-Apr-20 00:00:00
Started spooling to D:\oracle\product\11.2.0\dbhome_1\RDBMS\ADMIN\ash.html
二、ASH報告指標分析
ASH報告就非常直接了，直接給出等待事件和哪些SQL關聯，然后我們就可以拿SQL去調優了
圖來自《收獲，不止SQL優化》一書
