Oracle Essentials: Oracle9i, Oracle8i and Oracle8, Second Edition

Distributed Database Features

One of the strongest features of the Oracle database is its ability to scale up to handle extremely large volumes of data and users. Oracle scales not only by running on more and more powerful platforms, but also by running in a distributed configuration. Oracle databases on separate platforms can be combined to act as a single logical distributed database.

This section describes some of the basic ways that Oracle handles database interactions in a distributed database system.

Distributed Queries and Transactions

Data within an organization is often spread among multiple databases for reasons of both capacity and organizational responsibility. Users may want to query this distributed data or update it as if it existed within a single database.

Oracle first introduced distributed databases in response to the requirements for accessing data on multiple platforms in the early 1980s. Distributed queries can retrieve data from multiple databases. Distributed transactions can insert, update, or delete data on distributed databases. Oracle’s two-phase commit mechanism, which is described in detail in Chapter 12, guarantees that all the database servers that are part of a transaction will either commit or roll back the transaction. Distributed transactions that may be interrupted by a system failure are monitored by a recovery background process. Once the failed system comes back online, the same process will complete the distributed transactions to maintain ...