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Oracle11gr2新增版本功能(二)

原创 Linux操作系统 作者:yangtingkun 时间:2009-09-12 23:46:16 0 删除 编辑

11.2中,Oracle数据库引入的版本的概念,这为应用程序的升级提供了极大的方便。

这篇简单描述版本的实现和查询方式。

Oracle11gr2新增版本功能(一):http://yangtingkun.itpub.net/post/468/491458

 

 

前一篇简单描述了版本,下面接着上面的例子看看Oracle是如何实现这个功能的:

SQL> select synonym_name, table_name                   
  2  from user_synonyms;

SYNONYM_NAME                   TABLE_NAME
------------------------------ ------------------------------
S_1                            T

SQL> select object_id, object_name, object_type, edition_name
  2  from user_objects
  3  where object_name = 'S_1';

 OBJECT_ID OBJECT_NAME                    OBJECT_TYPE         EDITION_NAME
---------- ------------------------------ ------------------- ------------------------------
     74125 S_1                            SYNONYM             ORA$BASE

SQL> select sys_context('USERENV', 'CURRENT_EDITION_NAME')
  2  from dual;

SYS_CONTEXT('USERENV','CURRENT_EDITION_NAME')
-------------------------------------------------------------------------------------
ORA$BASE

下面设置版本为MY_EDITION

SQL> alter session set edition = my_edition;

会话已更改。

SQL> select synonym_name, table_name  
  2  from user_synonyms;

SYNONYM_NAME                   TABLE_NAME
------------------------------ ------------------------------
S_1                            T1

SQL> select object_id, object_name, object_type, edition_name
  2  from user_objects
  3  where object_name = 'S_1';

 OBJECT_ID OBJECT_NAME                    OBJECT_TYPE         EDITION_NAME
---------- ------------------------------ ------------------- ------------------------------
     74128 S_1                            SYNONYM             MY_EDITION

可以看到在USER_SYNONYMS视图中可以只能看到当前版本的同义词定义。而在USER_OBJECTS中可以看到,两个同义词的名称相同,但是两个对象的版本名称不同,而且OBJECT_ID并不相同,也就是说,二者实际上不是同一个对象。

SQL> select obj#, owner#, name, type#
  2  from sys.obj$
  3  where name = 'S_1';

      OBJ#     OWNER# NAME                                TYPE#
---------- ---------- ------------------------------ ----------
     74125         84 S_1                                     5
     74128         86 S_1                                     5

检查SYS.OBJ$发现,两个对象不但OBJECT_ID不同,连OWNER也是不同的。

SQL> select user#, name, type#, ext_username
  2  from sys.user$
  3  where user# in (84, 86);

     USER# NAME                                TYPE# EXT_USERNAME
---------- ------------------------------ ---------- ------------------------------
        84 YANGTK                                  1
        86 SYS_LNLQ7CWEC5SUF_0IC_Q_ONI8GO          2 YANGTK

当切换到不同的版本时,Oracle实际上切换到了不同的用户。

而用户查询的是当前版本的对象,这时由于很多的静态数据字典都发生了变化:

SQL> select text
  2  from dba_views
  3  where view_name = 'DBA_SYNONYMS';

TEXT
--------------------------------------------------------------------------------
select u.name, o.name, s.owner, s.name, s.node
from sys.user$ u, sys.syn$ s, sys."_CURRENT_EDITION_OBJ" o
where o.obj# = s.obj#
  and o.type# = 5
  and o.owner# = u.user#

可以看到,这些支持版本对象的数据字典信息,访问的系统表不再是SYS.OBJ$,而是另外一个对象:SYS._CURRENT_EDITION_OBJ

SQL> select owner, object_name, object_id, object_type
  2  from dba_objects
  3  where object_name = '_CURRENT_EDITION_OBJ';

OWNER                          OBJECT_NAME                     OBJECT_ID OBJECT_TYPE
------------------------------ ------------------------------ ---------- -------------------
SYS                            _CURRENT_EDITION_OBJ                 3070 VIEW

这个对象是一个视图,查看视图的定义:

SQL> select text
  2  from dba_views
  3  where view_name = '_CURRENT_EDITION_OBJ';

TEXT
--------------------------------------------------------------------------------
select o."OBJ#",o."DATAOBJ#",o."OWNER#",o."NAME",o."NAMESPACE",o."SUBNAME",o."TY
PE#",o."CTIME",o."MTIME",o."STIME",o."STATUS",o."REMOTEOWNER",o."LINKNAME",o."FL
AGS",o."OID$",o."SPARE1",o."SPARE2",o."SPARE3",o."SPARE4",o."SPARE5",o."SPARE6",

       o.spare3,
       case when (o.type# not in (4,5,7,8,9,10,11,12,13,14,22,87) or
                  bitand(u.spare1, 16) = 0) then
         null
       when (u.type# = 2) then
        (select eo.name from obj$ eo where eo.obj# = u.spare2)
       else
        'ORA$BASE'
       end
from obj$ o, user$ u
where o.owner# = u.user#
  and (   /* non-versionable object */
          (   o.type# not in (4,5,7,8,9,10,11,12,13,14,22,87,88)
           or bitand(u.spare1, 16) = 0)
          /* versionable object visible in current edition */
       or (    o.type# in (4,5,7,8,9,10,11,12,13,14,22,87)
           and (   (u.type# <> 2 and
                    sys_context('userenv', 'current_edition_name') = 'ORA$BASE')

                or (u.type# = 2 and
                    u.spare2 = sys_context('userenv', 'current_edition_id'))
                or exists (select 1 from obj$ o2, user$ u2
                           where o2.type# = 88
                             and o2.dataobj# = o.obj#
                             and o2.owner# = u2.user#
                             and u2.type#  = 2
                             and u2.spare2 =
                                  sys_context('userenv', 'current_edition_id'))
               )
          )
      )

ORACLE就是通过将这个视图代替了数据字典中的OBJ$对象,从而使得用户可以查询当前的版本信息。

 

来自 “ ITPUB博客 ” ,链接:http://blog.itpub.net/4227/viewspace-614521/,如需转载,请注明出处,否则将追究法律责任。

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