Oracle Essentials, 5th Edition

Chapter 13. Oracle Distributed Databases and Distributed Data

Data in large and mid-sized companies can sometimes be spread over many different databases. The data can be on different servers running different operating systems or even different database management systems. The data needed to answer any specific business question may need to be accessed from more than one server. A user may need to access this separate data on several servers simultaneously, or the data required for an answer may need to be moved to a local server. Inserts, updates, or deletions of data across these distributed servers may also be necessary.

There are two basic ways to deal with data in distributed databases: as part of a single distributed entity in which the distributed architecture is transparent, or by using a variety of replication or data transportation techniques to create copies of the data in more than one location. This chapter examines these options and the technologies associated with each solution.

Of course, there can be performance challenges when there is a need to access data distributed among multiple databases, sometimes referenced as “federated databases,” and especially where databases from multiple vendors are mixed. Years of database query optimization techniques, developed for single databases, must be reproduced through custom programming to ensure reasonable performance. So, queries across federated databases are often out of necessity rather than by design. Such queries ...