Cascaded Learned Bloom Filter for Optimizing Model-Filter Size Balance and Fast Rejection

Recent studies have demonstrated that learned Bloom filters (LBFs), which combine machine learning with the classical Bloom filter, can achieve superior memory efficiency. However, two challenges remain: (1) jointly optimizing the sizes of the machine learning model and Bloom filters, and (2) systematically minimizing reject time. We propose the Cascaded Learned Bloom Filter (CLBF), a unified architecture that generalizes existing LBF designs, including Sandwiched LBF and Partitioned LBF. Within this framework, we develop a dynamic programming-based optimizer that explores a discretized parameter space and identifies near-optimal configurations that balance model and filter sizes while achieving fast rejection. Experiments on real-world datasets show that CLBF reduces memory usage by up to 17% and decreases reject time by up to a factor of 65 compared to Partitioned LBF, the state-of-the-art LBF in terms of memory efficiency under a fixed machine learning model. Our code is publicly available at https://github.com/atsukisato/CascadedLBF.