Data in large and mid-sized companies can 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 techniques to create copies of the data in more than one location. This chapter examines both of these options and the technologies associated with each solution.
Users sometimes need to query or manipulate data that resides in multiple Oracle databases or in a mixture of Oracle and non-Oracle databases. This section describes a number of techniques and architectures you can use to interact with data in a distributed environment.
For many years, Oracle has offered access to distributed data residing on multiple Oracle database servers on multiple systems or nodes. Users don't ...