Oracle10g数据库自动诊断监视工具(ADDM)使用指南（一）--作者：fuyuncat

在炸老子就跑

第一章 ADDM简介
                 在Oracle9i及之前，DBA们已经拥有了很多很好用的性能分析工具，比如，tkprof、sql_trace、statspack、set event 10046&10053等等。这些工具能够帮助DBA很快的定位性能问题。但这些工具都只给出一些统计数据，然后再由DBA们根据自己的经验进行优化。
            那能不能由机器自动在统计数据的基础上给出优化建议呢？Oracle10g中就推出了新的优化诊断工具：数据库自动诊断监视工具（Automatic Database Diagnostic Monitor ADDM）和SQL优化建议工具（SQL Tuning Advisor STA）。这两个工具的结合使用，能使DBA节省大量优化时间，也大大减少了系统宕机的危险。简单点说，ADDM就是收集相关的统计数据到自动工作量知识库(Automatic Workload Repository AWR)中，而STA则根据这些数据，给出优化建议。例如，一个系统资源紧张，出现了明显的性能问题，由以往的办法，做个一个statspack快照，等30分钟，再做一次。查看报告，发现’ db file scattered read’事件在top 5 events里面。根据经验，这个事件一般可能是因为缺少索引、统计分析信息不够新、热表都放在一个数据文件上导致IO争用等原因引起的。根据这些经验，我们需要逐个来定位排除，比如查看语句的查询计划、查看user_tables的last_analysed子段，检查热块等等步骤来最后定位出原因，并给出优化建议。但是，有了STA以后，它就可以根据ADDM采集到的数据直接给出优化建议，甚至给出优化后的语句（抢了DBA的饭碗喽）。
ADDM能发现定位的问题包括：
         操作系统内存页入页出问题
         由于Oracle负载和非Oracle负载导致的CPU瓶颈问题
         导致不同资源负载的Top SQL语句和对象——CPU消耗、IO带宽占用、潜在IO问题、RAC内部通讯繁忙
         按照PLSQL和JAVA执行时间排的Top SQL语句.
         过多地连接 (login/logoff).
         过多硬解析问题——由于shared pool过小、书写问题、绑定大小不适应、解析失败原因引起的。
         过多软解析问题
         索引查询过多导致资源争用.
         由于用户锁导致的过多的等待时间 (通过包dbms_lock加的锁)
         由于DML锁导致的过多等待时间(例如锁住表了)
         由于管道输出导致的过多等待时间(如通过包dbms_pipe.put进行管道输出)
         由于并发更新同一个记录导致的过多等待时间(行级锁等待)
         由于ITL不够导致的过多等待时间（大量的事务操作同一个数据块）
         系统中过多的commit和rollback(logfile sync事件).
         由于磁盘带宽太小和其他潜在问题（如由于logfile太小导致过多的checkpoint，MTTR设置问题，过多的undo操作等等）导致的IO性能问题I
         对于DBWR进程写数据块，磁盘IO吞吐量不足
         由于归档进程无法跟上redo日至产生的速度，导致系统变慢
         redo数据文件太小导致的问题
         由于扩展磁盘分配导致的争用
         由于移动一个对象的高水位导致的争用问题
         内存太小问题——SGA Target, PGA, Buffer Cache, Shared Pool
         在一个实例或者一个机群环境中存在频繁读写争用的热块
         在一个实例或者一个机群环境中存在频繁读写争用的热对象
         RAC环境中内部通讯问题
         LMS进程无法跟上导致锁请求阻塞
         在RAC环境中由于阻塞和争用导致的实例倾斜
         RMAN导致的IO和CPU问题
         Streams和AQ问题
         资源管理等待事件

有一点要记住：AWR收集的数据时放到内存中（share pool），通过一个新的后台进程MMON定期写到磁盘中。所以10g的share pool要求比以前版本更大，一般推荐比以前大15-20%。另外，还要求系统参数STATISTICS_LEVEL设置为TYPICAL（推荐）或ALL;
ALTER SESSION SET STATISTICS_LEVEL= TYPICAL;

第二章 工作采集、诊断过程
Oracle10g提供了一个图形化的界面（通过OEM），使这个工具使用起来非常简单。下面这里介绍一下如何通过sqlplus使用这个工具。这个工具的使用非常简单，它是不需要安装的。
第一步：创建测试用的表
SQL> CREATE TABLE bigtab AS SELECT rownum as "id", a.* FROM dba_objects a;

Table created.

SQL> create table smalltab as select rownum as "id", a.* FROM dba_tables a;

Table created.

SQL> ALTER TABLE bigtab MODIFY (empno NUMBER);

Table altered.

SQL> DECLARE

2       n NUMBER;

3    BEGIN

4       FOR n IN 1..100

5       LOOP

6           INSERT INTO bigtab SELECT rownum as "id", a.* FROM dba_objects a;

7           COMMIT;

8       END LOOP;

9   END;
/

PL/SQL procedure successfully completed.

第二步：采集一次工作量快照
SQL> begin
  2   dbms_workload_repository.create_snapshot('TYPICAL');
  3  end;
  4  /

PL/SQL procedure successfully completed.

第三步：进行一些高负荷操作
DECLARE

    v_var number;

BEGIN

    FOR n IN 1..6

    LOOP

        select count(*) into v_var from bigtab b, smalltab a;

    END LOOP;

END;

/


PL/SQL procedure successfully completed.

第四步：再次采集一次工作量快照
要注意的是：两次快照之间的间隔时间必须足够（一般推荐30分钟左右），否则得到的ADDM报告中就会提示：THERE WAS NOT ENOUGH DATABASE TIME FOR ADDM ANALYSIS.
SQL> begin
  2   dbms_workload_repository.create_snapshot('TYPICAL');
  3  end;
  4  /

PL/SQL procedure successfully completed.

第五步：创建一个优化诊断任务并执行
先获取到两次快照的ID:
SQL> select snap_id from
  2  (SELECT * FROM dba_hist_snapshot
  3  ORDER BY snap_id desc)
  4  where rownum

SNAP_ID
--------
      66
      65

然后创建优化任务，并执行。

DECLARE

    task_name VARCHAR2(30) := 'DEMO_ADDM01';

    task_desc VARCHAR2(30) := 'ADDM Feature Test';

    task_id NUMBER;

BEGIN

    dbms_advisor.create_task('ADDM', task_id, task_name, task_desc, null);

    dbms_advisor.set_task_parameter(task_name, 'START_SNAPSHOT', 65);

    dbms_advisor.set_task_parameter(task_name, 'END_SNAPSHOT', 66);

    dbms_advisor.set_task_parameter(task_name, 'INSTANCE', 1);

    dbms_advisor.set_task_parameter(task_name, 'DB_ID', 1712582900);

    dbms_advisor.execute_task(task_name);

END;

/

PL/SQL procedure successfully completed.

其中，set_task_parameter是用来设置任务参数的。START_SNAPSHOT是起始快照ID，END_SNAPSHOT是结束快照ID，INSTANCE是实例号，对于单实例，一般是1，在RAC环境下，可以通过查询视图v$instance得到，DB_ID是数据库的唯一识别号，可以通过查询v$database查到。


第六步：查看优化建议结果
通知函数dbms_advisor.get_task_report可以得到优化建议结果。

SQL> SET LONG 1000000 PAGESIZE 0 LONGCHUNKSIZE 1000
SQL> COLUMN get_clob FORMAT a80
SQL> SELECT dbms_advisor.get_task_report('DEMO_ADDM01', 'TEXT', 'ALL') FROM DUAL;

DBMS_ADVISOR.GET_TASK_REPORT('
--------------------------------------------------------------------------------
          DETAILED ADDM REPORT FOR TASK 'DEMO_ADDM01' WITH ID 243
          -------------------------------------------------------

              Analysis Period: 23-NOV-2005 from 15:02:27 to 16:06:42
         Database ID/Instance: 1712582900/1
      Database/Instance Names: EDGAR/edgar
                    Host Name: HUANGED
             Database Version: 10.2.0.1.0
               Snapshot Range: from 65 to 66
                Database Time: 1463 seconds
        Average Database Load: .4 active sessions

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


FINDING 1: 100% impact (1463 seconds)
-------------------------------------
Significant virtual memory paging was detected on the host operating system.

   RECOMMENDATION 1: Host Configuration, 100% benefit (1463 seconds)
      ACTION: Host operating system was experiencing significant paging but no
         particular root cause could be detected. Investigate processes that
         do not belong to this instance running on the host that are consuming
         significant amount of virtual memory. Also consider adding more
         physical memory to the host.

FINDING 2: 100% impact (1463 seconds)
-------------------------------------
SQL statements consuming significant database time were found.

   RECOMMENDATION 1: SQL Tuning, 68% benefit (998 seconds)
      ACTION: Tune the PL/SQL block with SQL_ID "064wqx7c5b81z". Refer to the
         "Tuning PL/SQL Applications" chapter of Oracle's "PL/SQL User's Guide
         and Reference"
         RELEVANT OBJECT: SQL statement with SQL_ID 064wqx7c5b81z
         DECLARE
         v_var number;
         BEGIN
         FOR n IN 1..10000
         LOOP
         select count(*) into v_var from bigtab b, smalltab a;
         END LOOP;
         END;

   RECOMMENDATION 2: SQL Tuning, 67% benefit (986 seconds)
      ACTION: Run SQL Tuning Advisor on the SQL statement with SQL_ID
         "fvqfghq71cqns".
         RELEVANT OBJECT: SQL statement with SQL_ID fvqfghq71cqns and
         PLAN_HASH 3281046854
         SELECT COUNT(*) FROM BIGTAB B, SMALLTAB A
      RATIONALE: SQL statement with SQL_ID "fvqfghq71cqns" was executed 6
         times and had an average elapsed time of 166 seconds.

FINDING 3: 69% impact (1002 seconds)
------------------------------------
Time spent on the CPU by the instance was responsible for a substantial part
of database time.

   RECOMMENDATION 1: SQL Tuning, 67% benefit (986 seconds)
      ACTION: Run SQL Tuning Advisor on the SQL statement with SQL_ID
         "fvqfghq71cqns".
         RELEVANT OBJECT: SQL statement with SQL_ID fvqfghq71cqns and
         PLAN_HASH 3281046854
         SELECT COUNT(*) FROM BIGTAB B, SMALLTAB A
      RATIONALE: SQL statement with SQL_ID "fvqfghq71cqns" was executed 6
         times and had an average elapsed time of 166 seconds.
      RATIONALE: Average CPU used per execution was 162 seconds.

   RECOMMENDATION 2: SQL Tuning, 2.1% benefit (30 seconds)
      ACTION: Tune the PL/SQL block with SQL_ID "2b064ybzkwf1y". Refer to the
         "Tuning PL/SQL Applications" chapter of Oracle's "PL/SQL User's Guide
         and Reference"
         RELEVANT OBJECT: SQL statement with SQL_ID 2b064ybzkwf1y
         BEGIN EMD_NOTIFICATION.QUEUE_READY(:1, :2, :3); END;
      RATIONALE: SQL statement with SQL_ID "2b064ybzkwf1y" was executed 125
         times and had an average elapsed time of 0.26 seconds.
      RATIONALE: Average CPU used per execution was 0.24 seconds.

FINDING 4: 2.2% impact (33 seconds)
-----------------------------------
PL/SQL execution consumed significant database time.

   RECOMMENDATION 1: SQL Tuning, 2.2% benefit (33 seconds)
      ACTION: Tune the PL/SQL block with SQL_ID "2b064ybzkwf1y". Refer to the
         "Tuning PL/SQL Applications" chapter of Oracle's "PL/SQL User's Guide
         and Reference"
         RELEVANT OBJECT: SQL statement with SQL_ID 2b064ybzkwf1y
         BEGIN EMD_NOTIFICATION.QUEUE_READY(:1, :2, :3); END;
      RATIONALE: SQL statement with SQL_ID "2b064ybzkwf1y" was executed 125
         times and had an average elapsed time of 0.26 seconds.
      RATIONALE: Average time spent in PL/SQL execution was 0.26 seconds.


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

          ADDITIONAL INFORMATION
          ----------------------

Wait class "Application" was not consuming significant database time.
Wait class "Commit" was not consuming significant database time.
Wait class "Concurrency" was not consuming significant database time.
Wait class "Configuration" was not consuming significant database time.
Wait class "Network" was not consuming significant database time.
Wait class "User I/O" was not consuming significant database time.
Session connect and disconnect calls were not consuming significant database
time.
Hard parsing of SQL statements was not consuming significant database time.

The analysis of I/O performance is based on the default assumption that the
average read time for one database block is 10000 micro-seconds.


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

          TERMINOLOGY
          -----------

DATABASE TIME: This is the ADDM's measurement of throughput. From the user's
   point of view: this is the total amount of time spent by users waiting for
   a response from the database after issuing a call (not including
   networking). From the database instance point of view: this is the total
   time spent by forground processes waiting for a database resource (e.g.,
   read I/O), running on the CPU and waiting for a free CPU (run-queue). The
   target of ADDM analysis is to reduce this metric as much as possible,
   thereby reducing the instance's response time.

AVERAGE DATABASE LOAD: At any given time we can count how many users (also
   called 'Active Sessions') are waiting for an answer from the instance. This
   is the ADDM's measurement for instance load. The 'Average Database Load' is
   the average of the the load measurement taken over the entire analysis
   period. We get this number by dividing the 'Database Time' by the analysis
   period. For example, if the analysis period is 30 minutes and the 'Database
   Time' is 90 minutes, we have an average of 3 users waiting for a response.

IMPACT: Each finding has an 'Impact' associated with it. The impact is the
   portion of the 'Database Time' the finding deals with. If we assume that
   the problem described by the finding is completely solved, then the
   'Database Time' will be reduced by the amount of the 'Impact'.

BENEFIT: Each recommendation has a 'benefit' associated with it. The ADDM
   analysis estimates that the 'Database Time' can be reduced by the 'benefit'
   amount if all the actions of the recommendation are performed.

说明：
其中第五步到第六步可以直接执行$ORACLE_HOME/rdbms/admin/addmrpt.sql来得到，这个脚本的执行过程和statspack脚本执行过程类似：
SQL> @addmrpt

Current Instance
~~~~~~~~~~~~~~~~

   DB Id    DB Name      Inst Num Instance
----------- ------------ -------- ------------
1712582900 EDGAR               1 edgar


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

   DB Id     Inst Num DB Name      Instance     Host
------------ -------- ------------ ------------ ------------
* 1712582900        1 EDGAR        edgar        HUANGED

Using 1712582900 for database Id
Using          1 for instance number


Specify the number of days of snapshots to choose from
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Entering the number of days (n) will result in the most recent
(n) days of snapshots being listed.  Pressing  without
specifying a number lists all completed snapshots.



Listing the last 3 days of Completed Snapshots

                                                        Snap
Instance     DB Name        Snap Id    Snap Started    Level
------------ ------------ --------- ------------------ -----
edgar        EDGAR                7 22 Nov 2005 00:00      1
... ...
                                 64 23 Nov 2005 15:02      1
                                 65 23 Nov 2005 16:00      1
                                 66 23 Nov 2005 16:06      1


Specify the Begin and End Snapshot Ids
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Enter value for begin_snap: 65
Begin Snapshot Id specified: 66

Enter value for end_snap: 66
End   Snapshot Id specified: 66



Specify the Report Name
~~~~~~~~~~~~~~~~~~~~~~~
The default report file name is addmrpt_1_65_66.txt.  To use this name,
press  to continue, otherwise enter an alternative.

Enter value for report_name:

Using the report name addmrpt_1_65_66.txt


Running the ADDM analysis on the specified pair of snapshots ...


Generating the ADDM report for this analysis ...

... ...

此外，如果是RAC环境下，可以执行$ORACLE_HOME/rdbms/admin/addmrpti.sql，这脚本的执行，会多出要求输入DB ID和instance ID的要求。

     




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