Caching New Added 15 October 2026

Next.js: Failed to set Next.js data cache, items over 2MB can not be cached

The App Router stores fetch() responses in its data cache, and refuses any single response over 2MB. The page still renders, but that fetch runs again on every request, so a page you expected to be static quietly hits your API each time. It usually shows up when an endpoint grows past the limit, or when a whole collection is fetched only for a few fields to be used.

Quick fix

Read the commands before running them. Anything that restarts a service, deletes data or changes permissions should be tried on a non-production system first.

Quick fix

# Which request is too big? The log line includes the size
next build 2>&1 | grep -i 'over 2MB'
curl -s https://api.example.com/products | wc -c

# Fetch less: paginate or ask the API for only the fields you use
const res = await fetch('https://api.example.com/products?fields=id,name&limit=50');

# Or opt that call out of the data cache on purpose
const res = await fetch(url, { cache: 'no-store' });

# Or cache the trimmed result yourself rather than the raw response
import { unstable_cache } from 'next/cache';
const getProducts = unstable_cache(async () => (await (await fetch(url)).json()).map(p => ({ id: p.id, name: p.name })), ['products'], { revalidate: 3600 });

How to diagnose Caching errors

Cache problems are rarely reported as cache problems. They arrive as a traffic spike that takes down the origin (a stampede after a mass eviction), users seeing old content after a deploy, or an inexplicable 403 from the CDN. The unifying diagnostic is to look at the cache status header on a real response before theorising about anything else.

If the quick fix above does not resolve it, work through these steps. They apply to this whole class of error, not just to this one message, which is usually what saves the time.

Read the cache status header on a live request: curl -sI https://example.com | grep -i -E 'cache|age|x-cache|cf-cache-status'. HIT, MISS and BYPASS each point at a different root cause.
Check the Age header against your intended TTL. An Age larger than max-age means something is serving stale content deliberately (stale-while-revalidate), often the desired behaviour, occasionally the bug.
For stampedes, add request coalescing or a short randomised TTL jitter rather than a longer TTL. Identical expiry times across many keys are what create the thundering herd.
Use content-hashed filenames for static assets and no-cache for HTML. Almost every "users see the old version" incident traces back to a long TTL on an HTML document.
For CDN 403s, distinguish a CDN-generated response from an origin one by checking whether CDN-specific headers are present. An origin 403 has a completely different fix.

Tools worth reaching for

curl -sI
varnishlog
CDN edge logs
Cache-Control validators

Authoritative references

Primary documentation for this error, worth reading before applying any fix in production.

nextjs.org

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