In a distributed environment, replicating data accomplishes this goal. Rather than force
queries to cross the network to resolve user requests, selected data from remote servers is
replicated to the local server. This can be accomplished via a number of means, as described
in the following sections.
Replicated data is out of date as soon as it is created. Replicating data for performance
purposes is therefore most effective when the source data is very infrequently changed or when
the business processes can support the use of old data.
Oracle??™s distributed capabilities offer a means of managing the data replication within a
database. Materialized views replicate data from a master source to multiple targets. Oracle
provides tools for refreshing the data and updating the targets at specified time intervals.
Materialized views may be read-only or updatable. The management issues for materialized
views are covered in Chapter 17; in this section, you will see their performance-tuning aspects.
Before creating a materialized view for replication, you should first create a database link to
the source database. The following example creates a private database link called HR_LINK,
using the LOC service name:
create database link HR_LINK
connect to HR identified by ESNOTHR1968
using 'loc';
The create database link command, as shown in this example, has several parameters:
The name of the link (HR_LINK, in this case).
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