ORACLE数据库中Global Database Name与DB LINKS的关系还真是有点纠缠不清，在说清楚这个关系前，我们先来了解一下Global Database Name的概念
Global DataBase Name 概念
1. What is a global database name?
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The global database name is the unique name of the database. In a distributed
database system (a set of databases stored on multiple computers that typically
appears to applications as a single database) the global database name ensures
that each database is distinct from all other databases in the system. Oracle
forms a database's global database name by prefixing the database's network
domain with the individual database's name. For example: sales.us.oracle.com
and sales.uk.oracle.com.
The global database name defaults to DB_NAME.DB_DOMAIN and this value is marked
at database creation time. If you change the DB_NAME or DB_DOMAIN after the
database has been created, the value for the global database name (GLOBAL_NAME)
will not change.
说简单一点，global database name就是用来唯一标识数据库的东东。global database name由两部分组成，DB_NAME和DB_DOMAIN。在创建db link的时候，Oracle会自动将db_domain作为后缀添加上去。而且一旦加入就很难变更。所以在进行高级复制、Streams复制等配置时，最好首先将多个节点的global_name规划好。
如何查看Global Database Name
SQL> select * from global_name;
GLOBAL_NAME
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TEST.REGRESS.RDBMS.DEV.US.ORACLE.COM
SQL>