🔗 Judy arrays are patented

🔗 Computing

In computer science, a Judy array is a data structure implementing a type of associative array with high performance and low memory usage. Unlike most other key-value stores, Judy arrays use no hashing, leverage compression on their keys (which may be integers or strings), and can efficiently represent sparse data, that is, they may have large ranges of unassigned indices without greatly increasing memory usage or processing time. They are designed to remain efficient even on structures with sizes in the peta-element range, with performance scaling on the order of O(log n). Roughly speaking, Judy arrays are highly optimized 256-ary radix trees.

Judy trees are usually faster than AVL trees, B-trees, hash tables and skip lists because they are highly optimized to maximize usage of the CPU cache. In addition, they require no tree balancing and no hashing algorithm is used.

The Judy array was invented by Douglas Baskins and named after his sister.