cdn-caching

Run vercel metrics vercel.request.count grouped by cache_result, filtered to production. Treat HIT, STALE, and PRERENDER as cache-served and exclude BYPASS and unset values when computing the hit rate over cacheable traffic.

Stale content usually means stale-while-revalidate is active: a time-based revalidate interval elapsed or a tag was invalidated, so the old copy serves while regeneration runs in the background. Check the cacheReason field for stale_time, stale_tag, or stale_error to identify the trigger.

BYPASS means caching was skipped for that request, commonly due to no-store or private headers, cookies, Draft Mode, prerender-bypass tokens, or SEO crawler user agents. Draft Mode and crawler bypasses are expected behavior, not misconfiguration.

Prefer on-demand tag-based revalidation over short time-based intervals, and scope tags to specific IDs like product-123 instead of broad tags. Group isr_operation.write_units by route and cache_tags to find paths regenerating faster than they are read.

No. A PPR route has dynamic holes by definition, so even on a cached shell hit the function still runs to render the postponed content. Only a route with no holes serves as a pure prerender HIT without invoking the function.

Feature-flag and experiment precomputation creates distinct cache-key variants per flag combination, multiplying ISR entries across routes and PPR segments. Each variant misses on first hit per region, so collapsing the variant matrix or retiring finished experiments reduces misses.