Multi-copy Cuckoo Hashing

Dagang Li, Rong Du, Ziheng Liu, Tong Yang, Bin Cui

Abstract: Cuckoo hashing is widely used for its worst-case constant lookup performance even at very high load. However at high load, collision resolution will involve lots of probes on item relocation and may still fail in the end. To address the problem, we propose an efficient Cuckoo hashing scheme called Multi-copy Cuckoo or McCuckoo. Different from the blind kick-outs of standard Cuckoo hashing during a collision, we can foresee which way to successfully kick items by using multiple copies. Furthermore, with the knowledge of how many copies each item has in the table, we can identify impossible buckets and skip them during a lookup. In order to avoid expensive rehashing during insertion failures, McCuckoo also supports more efficient stash strategy that minimizes stash checking. McCuckoo uses simple logic and simple data structure, so it is suitable for both software and hardware implementation on platforms where intensive access to the slow and bandwidth limited off-chip external memory is the main bottleneck.