Scheduling of Reports
With proper scheduling these reports can be run extremely quickly using high degrees of parallelism. This allows the full power of the machine to be brought to bear on these reports, and the batch reports can be finished quickly. The canned queries are also predefined queries, but they differ from reports in that there is a requirement to run them online. Canned queries also differ from reports in that they are often parameterized, and hence the data set they visit can vary radically in size. As with the batch reports these queries are a good starting point for testing and development. You can measure the resource requirements of these queries, and the results can be used for capacity planning and for database design.
The canned queries are again good candidates for use on a pilot system, or for early delivery in a phased development. Ad hoc queries, as the name suggests, are the unpredictable element of a data warehouse. They are also generally the main reason for developing the data warehouse in the first place. It is exactly that ability to run any query when desired and expect a reasonable response that makes the data warehouse worthwhile, and makes the design such a significant challenge. The ad hoc query profile will be difficult if not impossible to predict. The best that can be done is to develop an understanding of the queries that are likely to be run. This will come from an understanding of the business and from the requirements capture. This information can then be used in the design of the database to meet those requirements.
