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Lesson 1

Features of Distributed Databases

The purpose of this module is to examine the new Oracle features related to distributed databases. As you know, Oracle software is evolving constantly to improve database connectivity between distributed systems. With the introduction of Oracle, we see several new features that improve connectivity between remote databases and offer improved security and replication reliability.
After completing this module, you will be able to:
  1. List primary Oracle enhancements for distributed databases
  2. Work with queue propagation
  3. Create primary key snapshots in replication
  4. Identify the new Oracle features for updateable snapshots
  5. Use deferred constraints on updateable snapshots
  6. Describe enhanced LOB support in Oracle
  7. Monitor replication by querying V$ views
  8. Implement snapshot security
  9. Walk through the steps for creating snapshots offline
  10. Identify the new features of snapshot deployment templates
The objective of this module is to provide you with enough detailed information about the new Oracle distributed features to enable you to use them in your organization and to understand their functions well enough to pass the OCT exam. This module assumes that you already have a baseline understanding of Oracle distributed database concepts, including snapshots and replication techniques.
Let's began by taking a closer look at each of the enhancements for distributed databases.


When an organization is geographically dispersed, it may choose to store its databases on a central database server or to distribute them to local servers (or a combination of both). A distributed database is a single logical database that is spread physically across computers in multiple locations that are connected by a data communications network. We emphasize that a distributed database is truly a database, not a loose collection of files. The distributed database is still centrally administered as a corporate resource while providing local flexibility and customization. The network must allow the users to share the data; thus a user (or program) at location A must be able to access (and perhaps update) data at location B. The sites of a distributed system may be spread over a large area (e.g., the United States or the world) or over a small area (e.g., a building or campus). The computers may range from PCs to large-scale servers or even supercomputers.
A distributed database requires multiple instances of a database management system (or several DBMSs), running at each remote site. The degree to which these different DBMS instances cooperate, or work in partnership, and whether there is a master site that coordinates requests involving data from multiple sites distinguish different types of distributed database environments.

Distributed Database Architecture

A distributed database system allows applications to access data from local and remote databases. In a homogenous distributed database system, each database is an Oracle Database. In a heterogeneous distributed database system, at least one of the databases is not an Oracle Database. Distributed databases use a client/server architecture to process information requests. This section contains the following topics:
  1. Homogenous Distributed Database Systems
  2. Heterogeneous Distributed Database Systems
  3. Client/Server Database Architecture