The service name (hq, in this example).
To use the newly created link, simply add it as a suffix to table names in commands. The
following example queries a remote table by using the HR_LINK database link:
select * from EMPLOYEES@hr_link
where office = 'ANNAPOLIS';
When you execute this query, Oracle will establish a session via the HR_LINK database link and
query the EMPLOYEES table in that database. The where clause will be applied to the EMPLOYEES
rows, and the matching rows will be returned. The execution of the query is shown graphically in
Figure 17-2.
The from clause in this example refers to EMPLOYEES@HR_LINK. Because the HR_LINK
database link specifies the server name, instance name, and owner name, the full name of the
table is known. If no account name had been specified in the database link, the user??™s account
name and password in the local database would have been used during the attempt to log into
the remote database.
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602 Oracle Database 11g DBA Handbook
The management of database links is described in the section ???Managing Distributed Data,???
later in this chapter.
Remote Data Manipulation: Two-Phase Commit
To support data manipulation across multiple databases, Oracle relies on Two-Phase Commit
(2PC). 2PC allows groups of transactions across several nodes to be treated as a unit; either the
transactions all commit or they all get rolled back. A set of distributed transactions is shown in
Figure 17-3.
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