Vercel CDN Achieves 10% Speed Increase and 15% Memory Reduction Through Bloom Filters

Vercel, a leading platform for frontend developers, recently announced a significant optimization to its Content Delivery Network (CDN), resulting in a 10% improvement in time-to-first-byte (TTFB) at the 75th percentile and a 15% reduction in memory usage. The company attributed these enhancements to the strategic application of Bloom filters, as detailed in a recent social media post. This development impacts the delivery of over 1 trillion monthly requests served by the platform.

The core of the optimization addresses a bottleneck in Vercel's global routing service, particularly for websites with a vast number of static paths. Previously, the service relied on parsing large JSON files to perform path lookups, which could take hundreds of milliseconds for complex sites, blocking the event loop and slowing down the entire routing service. This issue disproportionately affected large e-commerce sites or documentation platforms with extensive content.

To overcome this, Vercel implemented Bloom filters, a probabilistic data structure designed to efficiently test whether an element is a member of a set. As explained by Vercel, "By replacing a slow JSON parsing operation with a Bloom filter, we brought path lookup latency down to nearly zero and improved performance for everyone." Bloom filters offer a compact and rapid way to check for path existence, ensuring that only valid requests proceed to storage.

The impact of this change is substantial, with the 99th percentile duration for path lookup now approximately 0.5 milliseconds, a 200-fold improvement over the previous JSON parsing method. This dramatic reduction in latency for path lookups has had a ripple effect, decreasing the routing service's heap size and memory consumption by 15%. This, in turn, alleviated garbage collection pressure, further enhancing overall performance across the network.

These improvements ensure faster page loads and a smoother user experience across all websites hosted on Vercel, particularly benefiting those with complex structures. The company continues to leverage advanced engineering solutions to maintain high performance and scalability for its global user base.