Neverinfamous Memory Journal MCP Next Cache Components

Cache Components (Next.js 16+)

Note: Cache Components are available in Next.js canary. Verify cacheComponents is supported in your target version before applying this guidance.

Cache Components enable Partial Prerendering (PPR) - mix static, cached, and dynamic content in a single route.

Enable Cache Components

// next.config.ts
import type { NextConfig } from 'next'

const nextConfig: NextConfig = {
  cacheComponents: true,
}

export default nextConfig

This replaces the old experimental.ppr flag.

Three Content Types

With Cache Components enabled, content falls into three categories:

1. Static (Auto-Prerendered)

Synchronous code, imports, pure computations - prerendered at build time:

export default function Page() {
  return (
    <header>
      <h1>Our Blog</h1> {/* Static - instant */}
      <nav>...</nav>
    </header>
  )
}

2. Cached (use cache)

Async data that doesn't need fresh fetches every request:

async function BlogPosts() {
  'use cache'
  cacheLife('hours')

  const posts = await db.posts.findMany()
  return <PostList posts={posts} />
}

3. Dynamic (Suspense)

Runtime data that must be fresh - wrap in Suspense:

import { Suspense } from 'react'

export default function Page() {
  return (
    <>
      <BlogPosts /> {/* Cached */}
      <Suspense fallback={<p>Loading...</p>}>
        <UserPreferences /> {/* Dynamic - streams in */}
      </Suspense>
    </>
  )
}

async function UserPreferences() {
  const theme = (await cookies()).get('theme')?.value
  return <p>Theme: {theme}</p>
}

Selection Matrix: Static vs Cached vs Dynamic

When designing a component, use this matrix to determine the correct caching strategy:

use cache Directive

File Level

'use cache'

export default async function Page() {
  // Entire page is cached
  const data = await fetchData()
  return <div>{data}</div>
}

Component Level

export async function CachedComponent() {
  'use cache'
  const data = await fetchData()
  return <div>{data}</div>
}

Function Level

export async function getData() {
  'use cache'
  return db.query('SELECT * FROM posts')
}

Cache Profiles

Built-in Profiles

'use cache' // Default: 5m stale, 15m revalidate

'use cache: remote' // Platform-provided cache (Redis, KV)

'use cache: private' // For compliance, allows runtime APIs

cacheLife() - Custom Lifetime

import { cacheLife } from 'next/cache'

async function getData() {
  'use cache'
  cacheLife('hours') // Built-in profile
  return fetch('/api/data')
}

Built-in profiles: 'default', 'minutes', 'hours', 'days', 'weeks', 'max'

Inline Configuration

async function getData() {
  'use cache'
  cacheLife({
    stale: 3600, // 1 hour - serve stale while revalidating
    revalidate: 7200, // 2 hours - background revalidation interval
    expire: 86400, // 1 day - hard expiration
  })
  return fetch('/api/data')
}

Cache Invalidation

cacheTag() - Tag Cached Content

import { cacheTag } from 'next/cache'

async function getProducts() {
  'use cache'
  cacheTag('products')
  return db.products.findMany()
}

async function getProduct(id: string) {
  'use cache'
  cacheTag('products', `product-${id}`)
  return db.products.findUnique({ where: { id } })
}

updateTag() - Immediate Invalidation

Use when you need the cache refreshed within the same request:

'use server'

import { updateTag } from 'next/cache'

export async function updateProduct(id: string, data: FormData) {
  await db.products.update({ where: { id }, data })
  updateTag(`product-${id}`) // Immediate - same request sees fresh data
}

revalidateTag() - Background Revalidation

Use for stale-while-revalidate behavior:

'use server'

import { revalidateTag } from 'next/cache'

export async function createPost(data: FormData) {
  await db.posts.create({ data })
  revalidateTag('posts') // Background - next request sees fresh data
}

Runtime Data Constraint

Cannot access cookies(), headers(), or searchParams inside use cache.

Solution: Pass as Arguments

// Wrong - runtime API inside use cache
async function CachedProfile() {
  'use cache'
  const session = (await cookies()).get('session')?.value // Error!
  return <div>{session}</div>
}

// Correct - extract outside, pass as argument
async function ProfilePage() {
  const session = (await cookies()).get('session')?.value
  return <CachedProfile sessionId={session} />
}

async function CachedProfile({ sessionId }: { sessionId: string }) {
  'use cache'
  // sessionId becomes part of cache key automatically
  const data = await fetchUserData(sessionId)
  return <div>{data.name}</div>
}

Exception: use cache: private

For compliance requirements when you can't refactor:

async function getData() {
  'use cache: private'
  const session = (await cookies()).get('session')?.value // Allowed
  return fetchData(session)
}

Caching Security & Auth Boundaries

CRITICAL FAILURE MODE: Caching user-specific or authorization-bound data globally will leak PII (Personally Identifiable Information) across different users' sessions.

Rules for Auth Boundaries:

1. Never use standard 'use cache' for PII: Standard cache entries are shared globally. If a component fetches user profile data using an auth token, you MUST NOT use the standard global 'use cache'.
2. Explicitly include user identities in cache keys: If you must cache per-user data, extract the user ID in a dynamic context and pass it as an argument so it becomes part of the automatic cache key (e.g., async function CachedProfile({ userId }) { 'use cache'; ... }).
3. Use 'use cache: private' cautiously: This ensures data isn't shared across requests, but relies heavily on correct platform caching configuration.
4. Dynamic by default for Auth: For dashboards, settings, and secure data, default to Dynamic (Suspense) rather than Cached.

Cache Key Generation

Cache keys are automatic based on:

• Build ID - invalidates all caches on deploy
• Function ID - hash of function location
• Serializable arguments - props become part of key
• Closure variables - outer scope values included

async function Component({ userId }: { userId: string }) {
  const getData = async (filter: string) => {
    'use cache'
    // Cache key = userId (closure) + filter (argument)
    return fetch(`/api/users/${userId}?filter=${filter}`)
  }
  return getData('active')
}

Complete Example

import { Suspense } from 'react'
import { cookies } from 'next/headers'
import { cacheLife, cacheTag } from 'next/cache'

export default function DashboardPage() {
  return (
    <>
      {/* Static shell - instant from CDN */}
      <header>
        <h1>Dashboard</h1>
      </header>
      <nav>...</nav>

      {/* Cached - fast, revalidates hourly */}
      <Stats />

      {/* Dynamic - streams in with fresh data */}
      <Suspense fallback={<NotificationsSkeleton />}>
        <Notifications />
      </Suspense>
    </>
  )
}

async function Stats() {
  'use cache'
  cacheLife('hours')
  cacheTag('dashboard-stats')

  const stats = await db.stats.aggregate()
  return <StatsDisplay stats={stats} />
}

async function Notifications() {
  const userId = (await cookies()).get('userId')?.value
  const notifications = await db.notifications.findMany({
    where: { userId, read: false },
  })
  return <NotificationList items={notifications} />
}

Migration from Previous Versions

Migrating unstable_cache to use cache

unstable_cache has been replaced by the use cache directive in Next.js 16. When cacheComponents is enabled, convert unstable_cache calls to use cache functions:

Before (unstable_cache):

import { unstable_cache } from 'next/cache'

const getCachedUser = unstable_cache(async (id) => getUser(id), ['my-app-user'], {
  tags: ['users'],
  revalidate: 60,
})

export default async function Page({ params }: { params: Promise<{ id: string }> }) {
  const { id } = await params
  const user = await getCachedUser(id)
  return <div>{user.name}</div>
}

After (use cache):

import { cacheLife, cacheTag } from 'next/cache'

async function getCachedUser(id: string) {
  'use cache'
  cacheTag('users')
  cacheLife({ revalidate: 60 })
  return getUser(id)
}

export default async function Page({ params }: { params: Promise<{ id: string }> }) {
  const { id } = await params
  const user = await getCachedUser(id)
  return <div>{user.name}</div>
}

Key differences:

• No manual cache keys - use cache generates keys automatically from function arguments and closures. The keyParts array from unstable_cache is no longer needed.
• Tags - Replace options.tags with cacheTag() calls inside the function.
• Revalidation - Replace options.revalidate with cacheLife({ revalidate: N }) or a built-in profile like cacheLife('minutes').
• Dynamic data - unstable_cache did not support cookies() or headers() inside the callback. The same restriction applies to use cache, but you can use 'use cache: private' if needed.

Limitations

• Edge runtime not supported - requires Node.js
• Static export not supported - needs server
• Non-deterministic values (Math.random(), Date.now()) execute once at build time inside use cache

For request-time randomness outside cache:

import { connection } from 'next/server'

async function DynamicContent() {
  await connection() // Defer to request time
  const id = crypto.randomUUID() // Different per request
  return <div>{id}</div>
}

Sources:

• Cache Components Guide
• use cache Directive
• unstable_cache (legacy)

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