--- title: Request Collapsing product: vercel url: /docs/incremental-static-regeneration/request-collapsing canonical_url: "https://vercel.com/docs/incremental-static-regeneration/request-collapsing" last_updated: 2026-08-11 type: conceptual prerequisites: - /docs/incremental-static-regeneration related: - /docs/functions - /docs/caching/cdn-cache - /docs/headers/response-headers - /docs/caching/cache-control-headers - /docs/incremental-static-regeneration summary: "Learn how Vercel's CDN shields your origin during traffic surges for uncached routes." install_vercel_plugin: npx plugins add vercel/vercel-plugin --- # Request Collapsing Vercel uses **request collapsing** to protect uncached routes during high traffic. It reduces duplicate work by combining concurrent requests into a single function invocation within the same region. This feature is especially valuable for high-scale applications. ## Related pages > **For AI agents:** Follow these links to understand how this page connects to the rest of the Vercel ecosystem. For the full cross-link map (inbound, outbound, prerequisites, and semantic neighbors), see the .graph.md link below. - [Preventing the stampede: Request collapsing in the Vercel CDN ](https://vercel.com/blog/cdn-request-collapsing?from=related&source_path=%2Fdocs%2Fincremental-static-regeneration%2Frequest-collapsing&source_site=vercel-docs&relationship=related) - [How to reduce ISR revalidation costs](https://vercel.com/kb/guide/how-to-reduce-isr-revalidation-costs?from=related&source_path=%2Fdocs%2Fincremental-static-regeneration%2Frequest-collapsing&source_site=vercel-docs&relationship=related) — Reduce ISR costs by analyzing Incremental Static Regeneration \\(ISR\\) behavior to find pages and tags that revalidate to - [Request collapsing for ISR cache misses](https://vercel.com/changelog/request-collapsing-for-isr-cache-misses?from=related&source_path=%2Fdocs%2Fincremental-static-regeneration%2Frequest-collapsing&source_site=vercel-docs&relationship=related) - [Using Vercel as a Standalone CDN](https://vercel.com/kb/guide/using_vercel_as_a_cdn?from=related&source_path=%2Fdocs%2Fincremental-static-regeneration%2Frequest-collapsing&source_site=vercel-docs&relationship=related) — Use Vercel's external rewrites to proxy and cache content from external websites or APIs through Vercel's global edge ne - [Life of a Vercel request: Navigating the Edge Network](https://vercel.com/blog/life-of-a-vercel-request-navigating-the-edge-network?from=related&source_path=%2Fdocs%2Fincremental-static-regeneration%2Frequest-collapsing&source_site=vercel-docs&relationship=related) - [Behind the scenes of Vercel's infrastructure: Achieving optimal scalability and performance](https://vercel.com/blog/behind-the-scenes-of-vercels-infrastructure?from=related&source_path=%2Fdocs%2Fincremental-static-regeneration%2Frequest-collapsing&source_site=vercel-docs&relationship=related) - [Caching](https://vercel.com/docs/caching?from=related&source_path=%2Fdocs%2Fincremental-static-regeneration%2Frequest-collapsing&source_site=vercel-docs&relationship=related) — Learn how Vercel caches content across multiple layers to deliver fast responses and reduce load on your backend. - [How requests flow through Vercel](https://vercel.com/docs/fundamentals/infrastructure?from=related&source_path=%2Fdocs%2Fincremental-static-regeneration%2Frequest-collapsing&source_site=vercel-docs&relationship=related) — Learn how Vercel routes, secures, and serves requests from your users to your application. - [Cache Status and Reasons](https://vercel.com/docs/caching/cache-status?from=related&source_path=%2Fdocs%2Fincremental-static-regeneration%2Frequest-collapsing&source_site=vercel-docs&relationship=related) — Understand the cache status and reason shown for each request in Vercel logs, and what causes a response to miss, bypass - [Vercel fundamental concepts](https://vercel.com/docs/fundamentals?from=related&source_path=%2Fdocs%2Fincremental-static-regeneration%2Frequest-collapsing&source_site=vercel-docs&relationship=related) — Learn about the core concepts of Vercel - [Partial Prerendering \\(PPR\\)](https://vercel.com/docs/partial-prerendering?from=related&source_path=%2Fdocs%2Fincremental-static-regeneration%2Frequest-collapsing&source_site=vercel-docs&relationship=related) — Partial Prerendering serves a cached static shell instantly, then renders and streams the dynamic parts of a page per re Full cross-link map for this page: [/docs/incremental-static-regeneration/request-collapsing.graph.md](/docs/incremental-static-regeneration/request-collapsing.graph.md?from=related&source_path=%2Fdocs%2Fincremental-static-regeneration%2Frequest-collapsing&source_site=vercel-docs&relationship=graph) ## How request collapsing works When a request for an uncached path arrives, Vercel invokes the origin [function](/docs/functions) and stores the response in the [cache](/docs/caching/cdn-cache). In most cases, any following requests are served from this cached response. However, if multiple requests arrive while the initial function is still processing, the cache is still empty. Instead of triggering additional invocations, Vercel's CDN collapses these concurrent requests into the original one. They wait for the first response to complete, then all receive the same result. This prevents overwhelming the origin with duplicate work during traffic spikes and helps ensure faster, more stable performance. Vercel also applies request collapsing when serving [STALE](/docs/headers/response-headers#stale) responses (with [stale-while-revalidate](/docs/caching/cache-control-headers#stale-while-revalidate) semantics), ensuring that concurrent background revalidation of multiple requests is collapsed into a single invocation. ### Example Suppose a new blog post is published and receives 1,000 requests at once. Without request collapsing, each request would trigger a separate function invocation, which could overload the backend and slow down responses, causing a [**cache stampede**](https://en.wikipedia.org/wiki/Cache_stampede). With request collapsing, Vercel handles the first request, then holds the remaining 999 requests until the initial response is ready. Once cached, the response is sent to all users who requested the post. ## Supported features Request collapsing is supported for: - [Incremental Static Regeneration (ISR)](/docs/incremental-static-regeneration) - [Image Optimization](/docs/image-optimization) --- [View full sitemap](/docs/sitemap)