Saving 100 terabytes of memory by optimizing 1.1.1.1's DNS cache

Cloudflare optimized its 1.1.1.1 DNS cache by making five successive changes to how entries are stored in memory, reducing per-entry footprint by over 50% and freeing approximately 100 terabytes of memory across its fleet. The optimizations not only saved significant memory but also improved performance, with insert throughput rising 43% and lookup latency dropping 19%. The improvements were achieved by reducing overhead in data structures that store DNS cache entries, which at scale contain over 250 billion entries.