Materialization Optimizations for Feature Selection Workloads

There is an arms race in the data management industry to support statistical analytics. Feature selection, the process of selecting a feature set that will be used to build a statistical model, is widely regarded as the most critical step of statistical analytics. Thus, we argue that managing the feature selection process is a pressing data management challenge. We study this challenge by describing a feature selection language and a supporting prototype system that builds on top of current industrial R-integration layers. From our interactions with analysts, we learned that feature selection is an interactive human-in-the-loop process, which means that feature selection workloads are rife with reuse opportunities. Thus, we study how to materialize portions of this computation using not only classical database materialization optimizations but also methods that have not previously been used in database optimization, including structural decomposition methods (like QR factorization) and warmstart. These new methods have no analogue in traditional SQL systems, but they may be interesting for array and scientific database applications. On a diverse set of datasets and programs, we find that traditional database-style approaches that ignore these new opportunities are more than two orders of magnitude slower than an optimal plan in this new trade-off space across multiple R backends. Furthermore, we show that it is possible to build a simple cost-based optimizer to automatically select a near-optimal execution plan for feature selection.