Private Cache

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async function getRecommendations(productId: string) {
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  'use cache: private';
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  cacheTag(`recommendations-${productId}`);
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  cacheLife({ stale: 60 });
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  // Can call cookies() INSIDE the cached function!
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  const sessionId = (await cookies()).get('session-id')?.value || 'guest';
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  return getPersonalizedRecommendations(productId, sessionId);
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}
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async function Recommendations({ productId }: { productId: string }) {
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  // This will be runtime prefetched automatically
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  const recommendations = await getRecommendations(productId);
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  return (
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    <div>
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      {recommendations.map((rec) => (
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        <ProductCard key={rec.id} product={rec} />
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      ))}
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    </div>
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  );
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}
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export const unstable_prefetch = {
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  mode: 'runtime',
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  samples: [
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    { params: { id: '1' }, cookies: [{ name: 'session-id', value: '1' }] },
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  ],
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};

Demo

• Products labeled "Private Cache" link to pages that use use cache: private to enable runtime prefetching. The content is still dynamic, but it's prefetched when the static content of the page is also prefetched.
• Products labeled "No Private Cache" link to pages that don't use use cache: private, meaning their recommendations will be loaded after navigation.
• For demo purposes, the links display visual loading states:
  • Pink border with "Prefetching Private Cache..." when the runtime prefetch is in progress
  • Blue border with "Prefetched Private Cache" when the runtime prefetch has completed
  • Gray border for links without private cache
• With Private Cache: Personalized recommendations appear instantly (runtime prefetched).
• Without Private Cache: Recommendations show a loading skeleton, then appear after they're finished loading. The loading starts when the link is clicked.
• Click "Change Session" to get different personalized recommendations - notice how Private Cache links still runtime prefetch your new session's data.

Notes

• use cache: private enables runtime prefetching of personalized content by allowing request-specific APIs inside cached functions.
• Combine with unstable_prefetch export using mode: 'runtime' and appropriate cacheLife settings.

Visual Summary

Key Takeaways

Pitfalls & Tips

• Ensure cache lifetimes are long enough for prefetch to be useful.
• Avoid storing sensitive data in cache tags or logs.

Learn More

• Caching