Every request to Vercel passes through our CDN , which executes on average over 80 million routing instructions per second. Part of that work is looking up metadata to determine which paths exist and how to serve them. When that metadata isn’t cached, the CDN has to fetch it before it can serve the response.

We used to fetch and cache metadata one path at a time, retrieving only what each lookup needed. That seemed efficient at the time, but large deployments can contain hundreds of thousands of paths, each with its own cache entry. Every new deployment introduced fresh metadata, making cache misses a recurring cost for large sites that deployed frequently.

Fetching more metadata at once made these lookups faster. By grouping paths together, each fetch could populate the cache for many subsequent lookups. But fetching too much introduced its own costs.…