Oracle7 Server Distributed Systems Volume II: Replicated Data

Using Connection Qualifiers

Connection qualifiers provide a way to have several database links of the same type (for example, public) that point to the same remote database, yet establish those connections using different communications pathways (for example, an ethernet link or a modem link).

See Chapter 2 of Oracle7 Server Distributed Systems, Volume I for information about defining connection qualifiers for a database link.

In a replicated system, after the connection qualifier has been defined as described in Oracle7 Server Distributed Systems, Volume I, use the procedure CREATE_MASTER_REPGROUP in the DBMS_REPCAT package to create the master replication object group that will use that connection qualifier.

For example if you have defined the connection qualifier @ETHERNET and want to create the master replicated object group ACCT to use that qualifier:

DBMS_REPCAT.CREATE_MASTER_REPGROUP(

         gname          => 'acct',

         group_comment  => 'created by '||user||' on '||SYSDATE,

         master_comment => 'created by '||user||' on '||SYSDATE,

         qualifier      => '@ethernet')

When you create the snapshot replication group, use the CREATE_SNAPSHOT_REPGROUP procedure:

DBMS_REPCAT.CREATE_SNAPSHOT_REPGROUP(

     gname              => 'acct';

     master             => 'acct_hq.hq.com',

     comment            => 'created on ...',

     propagation_mode   => 'asynchronous',

     qualifier          => 'acct_hq.hq.com@ethernet');

After you generate replication support, replication for this site will occur via the ethernet connection specified by the connection qualifier @ETHERNET. The complete database link, with qualifier would look like this in a select statement:

SELECT * FROM emp@acct_hq.hq.com@ethernet;

If you have a concurrent modem link to ACCT_HQ.HQ.COM, you can also define a connection qualifier, @MODEM, and use the procedures above to create a master replication group and snapshot sites that update via the modem link. A select statement using the @MODEM connection qualifier would look like:

SELECT * FROM emp@acct_hq.hq.com@modem;

Attention: If you plan to use connection qualifiers, you will probably need to increase the value of the INIT.ORA parameter, OPEN_LINKS. The default is four open links per process. You will need to estimate the required value based on your usage. See the Oracle7 Server Reference for more information about the parameter OPEN_LINKS.