The Business Intelligence Blog

Bill Inmon writes on the virtual data warehouse. Interesting Read.

Why then is the virtual data warehouse such a supremely bad idea? There are actually lots of reasons for the vacuity of virtue manifested by the virtual data warehouse. Some of those reasons are:

A query that has to access a lot of databases simultaneously uses a lot of system resources. In the best of circumstances, query performance is a real problem.

A query that has to access a lot of databases simultaneously requires resources every time it is executed. If the query is run many times at all, the system overhead is very steep.

A query that has to access a lot of databases simultaneously is stopped dead in its tracks when it runs across a database that is down or otherwise unavailable.

A query that has to access a lot of databases simultaneously shuffles a lot of data around the system that otherwise would not need to be moved. The impact on the network can become very burdensome.

A query that has to access a lot of databases simultaneously is limited to the data found in the databases. If there is only a limited amount of historical data in the databases, the query is limited to whatever historical data is found there. For a variety of reasons, many application databases do not have much historical data to begin with.