Columnstore vs. SSAS

 

As part of a project that I have been engaged on recently, I have had the opportunity to test the performance difference between SQL Server 2014 Clustered Columnstore Indexes and SQL Server Analysis Services Multi-dimensional (MOLAP). To test the performance differences between the two technologies, I converted the three most CPU intensive MDX queries to T-SQL queries (Clustered Columnstore). Both sets of queries were then executed from cache, with a variety of predicate values, on identical hardware. Aggregate performance in seconds shown below:

It must be emphasized that the performance of Columnstore Indexes is dependent on many variables, including but not limited to calculation logic, number of distinct values, distribution of values, predicated values, and hardware IO throughput. In this case the queries involve the following calculations: exp(), sum(), and then log().

After testing the initial set of three queries, I then tested the performance of over 20 queries divided into 3 groups. These series of tests included several levels of aggregation with different predicate values as well.

Conclusion:

Even though Columnstore Indexes do not create pre-aggregates, like in SSAS multi-dimensional (MOLAP), under the right circumstances they can match or even out preform SSAS multi-dimensional. The performance increase is largely due to the highly efficient nature of the Columnstore Indexes being processed in “Batch” mode.

Tags: Clustered Columnstore, MOLAP, performance