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Incremental Static Regeneration (ISR)

Learn how Vercel's Incremental Static Regeneration (ISR) provides better performance and faster builds.
Table of Contents

Incremental Static Regeneration is available on all plans

Incremental Static Regeneration (ISR) allows you to create or update content on your site without redeploying. ISR's main benefits for developers include:

  1. Better Performance: Static pages can be consistently fast because ISR allows Vercel to cache generated pages in every region on our global Edge Network and persist files into durable storage
  2. Reduced Backend Load: ISR helps reduce backend load by using cached content to make fewer requests to your data sources
  3. Faster Builds: Pages can be generated when requested by a visitor or through an API instead of during the build, speeding up build times as your application grows

ISR is available to applications built with:

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Next.js will automatically create a Serverless Vercel Function that can revalidate when you add next: { revalidate: 10 } to the options object passed to a fetch request.

The following example demonstrates a Next.js page that uses ISR to render a list of blog posts:

Next.js (/app)
Next.js (/pages)
app/blog-posts/page.tsx
interface Post {
  title: string;
  id: number;
}
 
export default async function Page() {
  const res = await fetch('https://api.vercel.app/blog', {
    next: { revalidate: 10 },
  });
  const posts = (await res.json()) as Post[];
  return (
    <ul>
      {posts.map((post: Post) => {
        return <li key={post.id}>{post.title}</li>;
      })}
    </ul>
  );
}

To learn more about using ISR with Next.js in the App router, such as enabling on-demand revalidation, see the official Next.js documentation.

When using the Build Output API, the Serverless Vercel Functions generated for your ISR routes are called Prerender Functions.

Build Output API Prerender Functions are Serverless Functions with accompanying JSON files that describe the Function's cache invalidation rules. See our Prerender configuration file docs to learn more.

Both ISR and Cache-Control headers help reduce backend load by using cached content to make fewer requests to your data source. However, there are key architectural differences between the two.

  • Shared Global Cache: ISR has cache shielding built-in automatically, which helps improve the cache HIT ratio. The cache for your ISR route's Vercel Function output is distributed globally. In the case of a cache MISS, it looks up the value in a single, global bucket. With only cache-control headers, caches expire (by design) and are not shared across regions
  • 300ms Global Purges: When revalidating (either on-demand or in the background), your ISR route's Vercel Function is re-run, and the cache is brought up to date with the newest content within 300ms in all regions globally
  • Instant Rollbacks: ISR allows you to roll back instantly and not lose your previously generated pages by persisting them between deployments
  • Simplified Caching Experience: ISR abstracts common issues with HTTP-based caching implementations, adds additional features for availability and global performance, and provides a better developer experience for implementation

See our Cache control options docs to learn more about Cache-Control headers.

ISR vs Cache-Control comparison table
Feature
ISR
Caching Headers
On-demand purging & regeneration

Limited

Synchronized global purging

Limited

Support for fallbacks upon MISS

N/A

Durable storage

N/A

Atomic updates

N/A

Cache shielding

N/A

Slow origin protection

Limited

Automatic support for stale-if-error

Limited

Automatic support for stale-while-revalidate

Usage within popular frontend frameworks
Caching static page responses

On-demand revalidation is scoped to the domain and deployment where it occurs, and doesn't affect sub domains or other deployments.

For example, if you trigger on-demand revalidation for example-domain.com/example-page, it won't revalidate the same page served by sub domains on the same deployment, such as sub.example-domain.com/example-page.

See Revalidating across domains to learn how to get around this limitation.

When using ISR with a framework on Vercel, a Function is created based on your framework code. This means that using ISR incurs both Function usage as well as Fast Origin Transfer:

Explore your usage top paths to better understand ISR usage and pricing.

Last updated on July 24, 2024