Chanel [K]

面朝大海，春暖花开

How to Use DBMS_ADVANCED_REWRITE in Oracle 10g

with 4 comments

在Oracle10g之后，提供了DBMS_ADVANCED_REWRITE包，具有强大的查询重写功能，可以让我们在数据库层面实现很多微妙的调整。假设我们有一个应用，但是现在无法直接修改应用程序的编码，但是又想能够让应用程序的某些SQL产生我们想要的变化，那么就可以使用DBMS_ADVANCED_REWRITE包。

drop table t;
create table t as select object_id,object_name from dba_objects;
drop table t1;
create table t1 as select object_id,object_name from dba_objects where 1=0;
SQL> select count(*) from t;

  COUNT(*)
----------
     16636

SQL> select count(*) from t1;

  COUNT(*)
----------
         0

现在我们有表T和T1，表结构相同，但是表T中有1.6万记录，而表T1中没有记录，如果说我们的应用中有一个SQL多次地查询表T的总记录数，占用了大量的CPU和逻辑读，而这样的count记录数又是完全没有用处的，但是我们无法修改应用程序去掉这个SQL，那么我们就可以通过DBMS_ADVANCED_REWRITE包来讲查询表T的SQL转变为查询表T1，这样就大大减少了这条SQL的逻辑读。

首先DBMS_ADVANCED_REWRITE包的执行权限必须显式赋给需要的用户。

CONN sys/password AS SYSDBA

GRANT EXECUTE ON DBMS_ADVANCED_REWRITE TO kamus;

CONN kamus/password

BEGIN
  SYS.DBMS_ADVANCED_REWRITE.declare_rewrite_equivalence (
     name             => 't_rewrite',
     source_stmt      => 'SELECT count(*) FROM t',
     destination_stmt => 'SELECT count(*) FROM t1',
     validate         => FALSE,
     rewrite_mode     => 'TEXT_MATCH');
END;
/

然后需要设置会话层面的QUERY_REWRITE_INTEGRITY参数，该参数默认值为ENFORCED，表示只有重写后的SQL输出结果跟原结果完全一样时，查询才会被真正重写，在这里需要修改为TRUSTED。

SQL> ALTER SESSION SET QUERY_REWRITE_INTEGRITY = TRUSTED;
SQL> set autot on
SQL> select count(*) from t;

  COUNT(*)
----------
         0

Execution Plan
----------------------------------------------------------
Plan hash value: 238181912

----------------------------------------------------------------------------
| Id  | Operation           | Name | Rows  | Bytes | Cost (%CPU)| Time     |
----------------------------------------------------------------------------
|   0 | SELECT STATEMENT    |      |     1 |    13 |     2   (0)| 00:00:01 |
|   1 |  VIEW               |      |     1 |    13 |     2   (0)| 00:00:01 |
|   2 |   SORT AGGREGATE    |      |     1 |       |            |          |
|   3 |    TABLE ACCESS FULL| T1   |     1 |       |     2   (0)| 00:00:01 |
----------------------------------------------------------------------------

Note
-----
   - dynamic sampling used for this statement

Statistics
----------------------------------------------------------
          0  recursive calls
          0  db block gets
          3  consistent gets
          0  physical reads
          0  redo size
        417  bytes sent via SQL*Net to client
        416  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          1  rows processed

SQL> ALTER SESSION SET QUERY_REWRITE_INTEGRITY = ENFORCED;
SQL> select count(*) from t;

  COUNT(*)
----------
     16636

Execution Plan
----------------------------------------------------------
Plan hash value: 2966233522

-------------------------------------------------------------------
| Id  | Operation          | Name | Rows  | Cost (%CPU)| Time     |
-------------------------------------------------------------------
|   0 | SELECT STATEMENT   |      |     1 |    22   (0)| 00:00:01 |
|   1 |  SORT AGGREGATE    |      |     1 |            |          |
|   2 |   TABLE ACCESS FULL| T    | 16639 |    22   (0)| 00:00:01 |
-------------------------------------------------------------------

Note
-----
   - dynamic sampling used for this statement

Statistics
----------------------------------------------------------
          0  recursive calls
          0  db block gets
         69  consistent gets
          0  physical reads
          0  redo size
        420  bytes sent via SQL*Net to client
        416  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          1  rows processed

SQL>

可以看到在重写之后，执行计划中显示直接去查询表T1，而consistent gets也从查询表T需要的69减少为3。

可以从[USER|ALL|DBA]_REWRITE_EQUIVALENCES视图中获得查询重写的信息。

SQL> select * from user_rewrite_equivalences;

OWNER  NAME       SOURCE_STMT               DESTINATION_STMT          REWRITE_MO
------ ---------- ------------------------- ------------------------- ----------
KAMUS  T_REWRITE  SELECT count(*) FROM t    SELECT count(*) FROM t1   TEXT_MATCH

DBMS_ADVANCED_REWRITE包也有限制，不可以重写牵涉到SYS用户对象的SQL。

drop table t1;
create table t1 as select * from all_tables where 1=0;

SQL> BEGIN
  2    SYS.DBMS_ADVANCED_REWRITE.declare_rewrite_equivalence (
  3       name             => 't_rewrite',
  4       source_stmt      => 'SELECT count(*) FROM all_tables',
  5       destination_stmt => 'SELECT count(*) FROM t1',
  6       validate         => FALSE,
  7       rewrite_mode     => 'TEXT_MATCH');
  8  END;
  9  /
BEGIN
*
ERROR at line 1:
ORA-30354: Query rewrite not allowed on SYS relations
ORA-06512: at "SYS.DBMS_ADVANCED_REWRITE", line 29
ORA-06512: at "SYS.DBMS_ADVANCED_REWRITE", line 185
ORA-06512: at line 2

在测试中，如果destination_stmt中包含SYS用户对象，是可以成功创建查询重写的，但是在执行SQL的时候却会报ORA-03113错误，后台出现ORA-07445错误，无法正常执行。

SQL> BEGIN
  2    SYS.DBMS_ADVANCED_REWRITE.declare_rewrite_equivalence (
  3       name             => 't_rewrite',
  4       source_stmt      => 'SELECT count(*) FROM t1',
  5       destination_stmt => 'SELECT count(*) FROM all_tables',
  6       validate         => FALSE,
  7       rewrite_mode     => 'TEXT_MATCH');
  8  END;
  9  /

PL/SQL procedure successfully completed.

SQL> select * from user_rewrite_equivalences;

OWNER  NAME       SOURCE_STMT               DESTINATION_STMT          REWRITE_MO
------ ---------- ------------------------- ------------------------- ----------
KAMUS  T_REWRITE  SELECT count(*) FROM t1   SELECT count(*) FROM all_ TEXT_MATCH
                                            tables

SQL> ALTER SESSION SET QUERY_REWRITE_INTEGRITY = TRUSTED;

Session altered.

SQL> select count(*) from t1;
select count(*) from t1
*
ERROR at line 1:
ORA-03113: end-of-file on communication channel
Process ID: 8360
Session ID: 135 Serial number: 22

Written by kamus

March 12th, 2010 at 2:11 pm

Posted in Feeling

ORA-01017 When Connect SYSDBA by SQL Developer

without comments

在尝试使用SQL Developer用SYSDBA连接数据库时总是报ORA-01017错误。

ORA-01017: invalid username/password; logon denied

实际上用户名密码是正确的，并且在数据库服务器上使用SQL*Plus通过监听连接也是正常的。

C:\Users\Kamus>sqlplus "sys/oracle@orcl11g as sysdba"

SQL*Plus: Release 11.1.0.7.0 - Production on Fri Mar 12 12:17:01 2010

Copyright (c) 1982, 2008, Oracle.  All rights reserved.

Connected to:
Oracle Database 11g Enterprise Edition Release 11.1.0.7.0 - Production
With the Partitioning, OLAP and Real Application Testing options

SQL>

真正的问题是因为数据库密码文件缺失了。在windows下，Oracle数据库密码文件是储存在%ORACLE_HOME%\database目录下，命名为PWD%SID%.ora。

密码文件不存在，数据库实例完全可以正常启动，只是在尝试通过监听登陆SYSDBA的时候就会报ORA-01017错误。

那么为什么在本地使用SQL*Plus是正常的，这实际上是一个错觉，因为在Windows中Oracle默认安装以后会在sqlnet.ora文件中设置SQLNET.AUTHENTICATION_SERVICES = (NTS)，这表示支持“Windows NT native authentication”方式登陆数据库，也就是属于OSDBA组的Windows用户不用提供密码也可以通过SYSDBA登陆数据库。sqlnet.ora文件位于%ORACLE_HOME%\network\admin目录下。

我们随便使用一个不存在的用户名密码都是可以登录数据库的。

C:\Users\Kamus>sqlplus "NotExist/nopassword@orcl11g as sysdba"

SQL*Plus: Release 11.1.0.7.0 - Production on Fri Mar 12 13:10:49 2010

Copyright (c) 1982, 2008, Oracle.  All rights reserved.

Connected to:
Oracle Database 11g Enterprise Edition Release 11.1.0.7.0 - Production
With the Partitioning, OLAP and Real Application Testing options

SQL>

修改SQLNET.AUTHENTICATION_SERVICES参数为NONE之后。

SQLNET.AUTHENTICATION_SERVICES = (NONE)

再次测试用SQL*Plus登陆，报ORA-01031错误，即使提供正确的SYS用户密码也会报同样的错误，因为此时密码文件不存在，不能通过密码文件校验SYS用户密码是否正确，而又不允许通过NTS方式登陆数据库。

C:\Users\Kamus>sqlplus "NotExist/nopassword@orcl11g as sysdba"

SQL*Plus: Release 11.1.0.7.0 - Production on Fri Mar 12 13:14:07 2010

Copyright (c) 1982, 2008, Oracle.  All rights reserved.

ERROR:
ORA-01031: insufficient privileges

Enter user-name:

重新创建密码文件，保持sqlnet.ora文件中SQLNET.AUTHENTICATION_SERVICES = (NONE)。

orapwd file=D:\oracle\product\11.1.0\db_1\database\PWDorcl11g.ora password=oracle

这样就只能通过正确的SYS用户和密码才可以用SYSDBA登陆数据库了。

C:\Users\Kamus>sqlplus / as sysdba

SQL*Plus: Release 11.1.0.7.0 - Production on Fri Mar 12 13:18:32 2010

Copyright (c) 1982, 2008, Oracle.  All rights reserved.

ERROR:
ORA-01031: insufficient privileges

Enter user-name:
C:\Users\Kamus>
C:\Users\Kamus>sqlplus sys/oracle as sysdba

SQL*Plus: Release 11.1.0.7.0 - Production on Fri Mar 12 13:18:44 2010

Copyright (c) 1982, 2008, Oracle.  All rights reserved.

Connected to:
Oracle Database 11g Enterprise Edition Release 11.1.0.7.0 - Production
With the Partitioning, OLAP and Real Application Testing options

SQL>

同样在这种配置下，SQL Developer也可以正常用SYSDBA登陆数据库了。

Written by kamus

March 12th, 2010 at 1:19 pm

Posted in Oracle RDBMS

Tagged with ,

ACOUG！

with 12 comments

有感于国外Oracle用户组的发达，我跟eygle从今年开始尝试组建中国的Oracle用户组，All China Oracle User Group。我们的站点是acoug.org。

我们希望能够为全中国的Oracle技术爱好者提供一个交流与活动的平台，我们希望能够激发更多人对于Oracle技术以及相关知识的兴趣，我们希望沉浸在这些技术中的人员获得更多的乐趣。这是我跟eygle一直以来的一个理想，但愿我们能为此付出并且有所回报。

我们认识到中国目前掌握Oracle技术的人员广度和深度都跟美国、欧洲甚或是印度存在着较大差距，这需要我们更有热情的去付出，但愿在不久的将来ACOUG在全球Oracle用户组中占据一席之地。

ACOUG计划定期举行线下活动，而线下活动也将是ACOUG未来工作的重点，邀请著名的业内人士（不仅限于国内）来进行主题演讲，并围绕相关主题进行广泛的讨论从而使更多人获益。

eygle的文章有关于ACOUG更多的阐述，请猛击这里。

预计在这个月的3月20日（周六）开展ACOUG第一次线下活动，详细的地点、场地以及演讲主题还未确定，但是请有兴趣的朋友时刻关注ACOUG网站，欢迎参加。

Written by kamus

March 6th, 2010 at 10:25 pm

Posted in Oracle RDBMS