SQL & PL/SQL

A distributed database environment is an environment that has two or more databases. Optionally, these databases must communicate over the network using such things as Oracle Net, but really could be on the same server communicating with IPC.

In the old days, I had data about leased property in one database but some other guy had "family leased housing" in his database, so we had to write some links to merry up the data and product such results as "the total cost of all leased property."

Suppose you have two Oracle databases, each with important data, and now you need to combine the data for some reason, such as reporting or because one of the databases has all of your reference tables and the other just has data tables (yes, some people do that, and it works like the hub-and-spoke system that caused so many airlines to go bankrupt :) ) Anyways, all you have to do is create a database link in database A that points to database B. Now, you can do things like SELECT * FROM MYTABLE@B.

Distributed databases form the basis for advanced topics like Oracle Advanced Replication (multi-master and snapshot) and Oracle Streams. These docs will tell you about init.ora parameters you need to look at, as well as tuning issues to be considered.

-Mark
9i OCP

In addition, I think you need to set distributed_transactions to something greater than zero if you plan to update or insert on the database thru the dblink.