  The distribution of keys to a given number of buckets is a fundamental task
in distributed data processing and storage. A simple, fast, and therefore
popular approach is to map the hash values of keys to buckets based on the
remainder after dividing by the number of buckets. Unfortunately, these
mappings are not stable when the number of buckets changes, which can lead to
severe spikes in system resource utilization, such as network or database
requests. Consistent hash algorithms can minimize remappings, but are either
significantly slower than the modulo-based approach, require floating-point
arithmetic, or are based on a family of hash functions rarely available in
standard libraries. This paper introduces JumpBackHash, which uses only integer
arithmetic and a standard pseudorandom generator. Due to its speed and simple
implementation, it can safely replace the modulo-based approach to improve
assignment and system stability. A production-ready Java implementation of
JumpBackHash has been released as part of the Hash4j open source library.
