Extracting data from virtual data warehouses: a practical aproach of how to improve query performance

The Business Intelligence project's team is always confronted with a major problem: low performance in data extraction from data warehouses. This problem can be critical because of the major impact in the using the data from data warehouse: if a BI report is taking a lot of time to run then it is useless or the data displayed are no longer available for taking critical decisions, so the project can be compromised. In this case there are several techniques that can be applied to reduce queries' execution time and to improve the performance of the BI analyses and reports. In this paper we present an overview of an implementation of a Business Intelligence project in a national company, the problems we confronted with and the techniques that we applied to reduce the cost of execution for improving query performance in this decisional support system.