Improving Query Performance in Virtual Data Warehouses

In order to improve the quality of Business Intelligence Systems in an organization we can choose to build the system using BI techniques such as OLAP and data warehousing or by using traditional reports based on SQL queries. The cost and developing time for BI tools is greater than those for SQL Reports and these factors are important in taking decisions on what type of techniques we used for BIS, also the problem of low performance in data extraction from data warehouse 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 or the data displayed are no longer available for taking critical decisions, 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. Key-Words: Tuning and optimization, SQL query plans, Business Intelligence projects, Virtual data warehouse, Data extraction, Query optimization and performance, Partitioning techniques, Indexes, Analytical functions