About Assigning Logical Table Sources Priority Order

Priority numbers determine which logical table source is used to answer a query.

For example, you might have user queries that are fulfilled by both a data warehouse and an OLTP source. Often access to an operational system is expensive, while access to a data warehouse is cheap. In this situation, you can assign a higher priority to the data warehouse to ensure that all queries are fulfilled by the data warehouse if possible.

Although the logical table source priority is the metric that the Oracle Analytics query engine considers before any other cost metric, the table source's priority group doesn't always determine that a particular query is fulfilled by that source. The Oracle Analytics query engine uses other factors to determine which logical table source to use for a query. See How Are Fact Logical Table Sources Selected to Answer a Query? and How Are Dimension Logical Table Sources Selected to Answer a Query?

To assign priority group numbers, you rank your logical table sources in numeric order, with 0 being the highest-priority source. You can assign the same number to multiple sources to create a priority group. For example, you can have two logical table sources in priority group 0, two logical table sources in priority group 1, and so on. In most cases only two priority groups (0 and 1) are needed.

Assigning priority groups is optional.

It's important that you don't use priority groups as a method of fine tuning the choice of logical table sources used to answer queries. The Oracle Analytics query engine tries to automatically use the most optimal logical table sources, but only within the same priority group. When you set a different priority group to each logical table source, it might cause the Oracle Analytics query engine to use suboptimal logical table sources.