Addition of a Secondary Functional Bloom Filter

Key-value data structures have been extensively used in various applications. When a large amount of data needs to be compactly stored in a fixed memory size, a functional Bloom filter is a space-efficient key-value structure. In this letter, we propose a 2-stage functional Bloom filter structure composed of a primary functional Bloom filter and a secondary functional Bloom filter to resolve the indeterminables produced from the primary functional Bloom filter. We analytically present the memory ratio allocated for each of the two Bloom filters to achieve the lowest search failure rate. The analytical result is validated through experiments, thereby demonstrating that the optimal performance is realized when the secondary functional Bloom filter uses 3% of the total memory.