Bitmap Filtering in the Fabric Data Warehouse

Bitmap filtering is a technique used to accelerate queries that contain hash-based joins. Beyond simple select-project-join queries, bitmap filters can also be applied to more complex query patterns, sometimes achieving performance comparable to alternative plans that query engines may not otherwise consider. At the same time, placing bitmap filters as a post-processing step after optimization can result in suboptimal choices. In this paper, we describe how local and distributed bitmap filters are integrated in the Microsoft Fabric Data Warehouse (or Fabric DW). We highlight challenges and solutions in the spaces of optimization, scheduling, and execution. We complement our presentation with an experimental evaluation over synthetic benchmarks and real data workloads that validate our approach.