C^2: Cache-Conscious Succinct Tries with Adaptive Unary Path Compression

2026-06-14

AI Summary

This work addresses two key limitations of existing succinct tries: poor cache locality and excessive space consumption due to unary paths. To overcome these issues, we introduce two core techniques: C₁, a cache-aware bitvector layout that enhances query locality, and C₂, an adaptive unary path compression scheme that reduces redundant storage. We integrate both optimizations into three widely used succinct trie implementations—FST, CoCo-trie, and Marisa. Experimental results demonstrate that C₁ accelerates query performance by 1.12× to 1.58×, while C₂ achieves an average memory reduction of 23%. Collectively, our approach outperforms both state-of-the-art succinct and non-succinct trie variants in terms of overall efficiency.

Abstract

Succinct tries are powerful string dictionaries because of their low memory footprint and fast query performance. However, existing succinct trie implementations face two key challenges to spatial locality: 1) they incur unnecessary cache misses during queries, especially during trie navigation operations, and 2) they waste significant space when the data contains many unary paths. We propose C^2, a set of two techniques: C_1 introduces a more cache-friendly layout for the \bv underlying succinct tries, and C_2 compresses redundant unary paths. We thoroughly redesign three state-of-the-art succinct tries: FST, CoCo-trie, and Marisa, producing C^2-FST, C^2-CoCo, and C^2-Marisa. Experiments on six diverse datasets show that the C_1 optimization improves query performance by 1.58x, 1.12x, and 1.42x, respectively, compared to the original FST, CoCo-trie, and Marisa. Furthermore, the C_2 optimization achieves a 1.3x smaller memory footprint on average. The succinct tries optimized with both aspects of C^2 achieve better space-time tradeoffs than their original versions and other state-of-the-art succinct tries, while using significantly less space than non-succinct tries like ART and C-ART.

Problem

• succinct tries
• cache misses
• unary paths
• spatial locality
• memory footprint

Innovation

• cache-conscious layout
• unary path compression
• succinct tries
• spatial locality
• adaptive compression