Performance-optimal filtering

Abstract

We define the concept of performance-optimal filtering to indicate the Bloom or Cuckoo filter configuration that best accelerates a particular task. While the space-precision tradeoff of these filters has been well studied, we show how to pick a filter that maximizes the performance for a given workload. This choice might be "suboptimal" relative to traditional space-precision metrics, but it will lead to better performance in practice. In this paper, we focus on high-throughput filter use cases, aimed at avoiding CPU work, e.g., a cache miss, a network message, or a local disk I/O - events that can happen at rates of millions to hundreds per second. Besides the false-positive rate and memory footprint of the filter, performance optimality has to take into account the absolute cost of the filter lookup as well as the saved work per lookup that filtering avoids; while the actual rate of negative lookups in the workload determines whether using a filter improves overall performance at all. In the course of the paper, we introduce new filter variants, namely the register-blocked and cache-sectorized Bloom filters. We present new implementation techniques and perform an extensive evaluation on modern hardware platforms, including the wide-SIMD Skylake-X and Knights Landing. This experimentation shows that in high-throughput situations, the lower lookup cost of blocked Bloom filters allows them to overtake Cuckoo filters.