The dataset designer has less control over the performance of DirectQuery datasets given that data storage and query execution is the responsibility of the source system. However, dataset designers can ensure that the DAX functions used in measures take advantage of the source system resources and can partner with source system owners and experts to test alternative data source optimizations, such as the columnstore index for SQL Server. Additionally, as advised earlier regarding the Assume Referential Integrity relationship property, performance can be significantly improved by generating inner-join SQL statements.