当指定了db_domain的时候，在创建db link时会自动在db_link的后面加上db_domain（doc：
If you omit the domains from the name of a database link， Oracle expands the name by qualifying the database with the domain of your local database as it currently exists in the data dictionary， and then stores the link name in the data dictionary. The characters valid in a database domain name are： alphanumeric characters， underscore （_）， and number sign （#）。
），9i好像记得是这样的，但是10g我验证了一下不是：
SQL> create database link dbl_test using 'orcl'；
数据库链接已创建。
SQL> select db_link from dba_db_links；
DB_LINK
----------------------------------------------------------------------------
DBL
DBL_TEST
ORCL
还有一点需要主要的是：You must set this parameter for every instance， and multiple instances must have the same value in Real Application Clusters
6、global_name 全局数据库名
global_name 是由db_name.db_domain构成的，doc如下：
| 以下是引用片段： Understanding How Global Database Names Are Formed A global database name is formed from two components: a database name and a domain. The database name and the domain name are determined by the following initialization parameters at database creation: Component Parameter Requirements Example Database name DB_NAME Must be eight characters or less. sales Domain containing the database DB_DOMAIN Must follow standard Internet conventions. Levels in domain names must be separated by dots and the order of domain names is from leaf to root, left to right. us.acme.com |
但是通过验证发现oracle并没有把db_name.db_domain和global_name 同步起来，不知道为什么？global_name oracle是通过提供了一个view，sys.global_name，该试图是源于props$的，可以查看创建view的脚本，最终我们访问的是一个public synonym global_name：
