You can manipulate and query data from remote databases. However, it is not desirable to have large volumes of data constantly sent from one database to another. To reduce the amount of data being sent across the network, you should consider different data replication options.
In a purely distributed environment, each data element exists in one database. When data is
required, it is accessed from remote databases via database links. This purist approach is similar to implementing an application strictly in
third normal form
, an approach that will not easily support any major production application. Modifying the application's tables to improve data retrieval performance involves denormalizing data. The denormalization process deliberately stores redundant data in order to shorten users’ access paths to the data.
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 Replicated data is out of date as soon as it is created.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.