Infinispan makes use of a consistent hash function to place nodes on a hash wheel, and to place keys of entries on the same wheel to determine where entries live.
In Infinispan 4.2 and earlier, the hash space was hardcoded to 10240, but since 5.0, the hash space is Integer.MAX_INT. Please note that since Hot Rod clients should not assume a particular hash space by default, everytime a hash-topology change is detected, this value is sent back to the client via the Hot Rod protocol.
When interacting with Infinispan via the Hot Rod protocol, it is mandated that keys (and values) are byte arrays, to ensure platform neutral behavior. As such, smart-clients which are aware of hash distribution on the backend would need to be able to calculate the hash codes of such byte array keys, again in a platform-neutral manner. To this end, the hash functions used by Infinispan are versioned and documented, so that it can be re-implemented by non-Java clients if needed.
The version of the hash function in use is provided in the Hot Rod protocol, as the hash function version parameter.
Version 1 (single byte, 0x01)
The initial version of the hash function in use is Austin Appleby's MurmurHash 2.0 algorithm, a fast, non-cryptographic hash that exhibits excellent distribution, collision resistance and avalanche behavior. The specific version of the algorithm used is the slightly slower, endian-neutral version that allows consistent behavior across both big- and little-endian CPU architectures. Infinispan's version also hard-codes the hash seed as -1. For details of the algorithm, please visit Austin Appleby's MurmurHash 2.0 page. Other implementations are detailed on Wikipedia. This hash function was the default one used by the Hot Rod server until Infinispan 4.2.1.
Version 2 (single byte, 0x02)
Since Infinispan 5.0, a new hash function is used by default which is Austin Appleby's MurmurHash 3.0 algorithm. Detailed information about the hash function can be found in this wiki. Compared to 2.0, it provides better performance and spread.