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Judy array

In computer science, a Judy array is an early-2000s Hewlett-Packard hand-optimized implementation of a 256-ary radix tree that uses many situational node types to reduce latency from CPU cache-line fills. As a compressed radix tree, a Judy array can store potentially sparse integer- or string-indexed data with comparatively low memory usage and low read latency, without relying on hashing or tree balancing, and without sacrificing in-order traversal. Per-operation latency scales as O(\log n) —as expected of a tree—and the leading constant factor is small enough that Judy arrays are suitable even to the peta-element range. When applicable, they can be faster than implementations of AVL trees, B-trees, hash tables, or skip lists from the same time period.

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Article summary

In computer science, a Judy array is an early-2000s Hewlett-Packard hand-optimized implementation of a 256-ary radix tree that uses many situational node types to reduce latency from CPU cache-line fills. As a compressed radix tree, a Judy array can store potentially sparse integer- or string-indexed data with comparatively low memory usage and low read latency, without relying on hashing or tree balancing, and without sacrificing in-order traversal. Per-operation latency scales as O(\log n) —as expected of a tree—and the leading constant factor is small enough that Judy arrays are suitable even to the peta-element range. When applicable, they can be faster than implementations of AVL trees, B-trees, hash tables, or skip lists from the same time period.

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  1. Summarise the article in your own words. Which single claim would you verify first, and why?
  2. Which claim in this article is most likely to be revised as the sources update? How would you check its current status?
  3. If two sources disagreed about one of these facts, what would you need in order to trust one over the other?

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