I think this could be used as a lightweight bloom filter. One direct use-case I see is to build a cache of keys from some _other_ database during initialization

I think this could be used as a lightweight bloom filter. One direct use-case I see is to build a cache of keys from some _other_ database during initialization. In cases where the read exceeds write, such as genomic data processing, this can provide additional performance gain, as opposed to querying the database. While redis _can_ be used, I think that this having a much smaller codebase is advantageous, in case one wishes to implement additional domain-specific requirements. Nice work!