Tabaka gani za cache zilizopo katika Next.js?

Question

Accepted Answer

App Router ina **tabaka kadhaa za cache** zinazolingana. Kuelewa zao kunaeleza kwa nini data wakati mwingine inaonekana kuwa stale na jinsi ya kudhibiti upya.

## Cache nne

```text
1. Request Memoization — dedupes identical fetch() calls within ONE render pass
2. Data Cache          — persists fetch() results across requests & deploys (server)
3. Full Route Cache    — caches the rendered HTML/RSC of static routes (build time)
4. Router Cache        — client-side cache of visited routes (in the browser, per session)
```

## 1. Request Memoization

```tsx
// the SAME fetch in a layout AND a page → only ONE network request per render
const user = await fetch("/api/user"); // automatically deduped
```

## 2. Data Cache (ile unayorekezesha zaidi)

```tsx
fetch(url, { cache: "force-cache" });       // cached (default) — like SSG
fetch(url, { cache: "no-store" });          // never cached — fresh every request
fetch(url, { next: { revalidate: 60 } });   // cached, refreshed every 60s — ISR
fetch(url, { next: { tags: ["posts"] } });  // taggable for on-demand invalidation
```

## 3 na 4. Route cache

**Full Route Cache** inahifadhi njia zilizofungwa kwa chuo; **Router Cache** inahifadhi njia zilizokuwa zikidhaliliwa hapo awali kwenye kivinjari ili kurudi nyuma/mbele na urekebishaji wa haraka unakuwa haraka.

## Kuakabili cache kwenye mabadiliko

```tsx
import { revalidatePath, revalidateTag } from "next/cache";

revalidatePath("/blog");        // invalidate a specific route's cache
revalidateTag("posts");         // invalidate every fetch tagged "posts"
router.refresh();               // (client) clear the Router Cache for current route
```

Baada ya kuunda/kusasisha data (mara nyingi katika Server Action), unakitaka `revalidatePath`/`revalidateTag` ili kurasa zilizathiriwa ziweze kupata tena na watumiaji kuona mabadiliko.

## Tatizo la kawaida

```text
"Why is my data stale after an update?" → a cache (usually Data or Router cache)
is serving the old value. Fix: revalidateTag/revalidatePath after the mutation,
or use cache: "no-store" for always-fresh data.
```

(Kumbuka: defaults za cache zimebadilika katika Next versions - angalia toleo lako, kwani baadhi ya versions za hivi karibuni zinakubuza mara chache kwa default.)

## Kwa nini inastahili kuchukuliwa

Caching ya Next.js katika tabaka nyingi kwa mikakati ni kile kinachofanya kuwa haraka, lakini pia ni chanzo #1 cha kuchanganyikiwa "kwa nini data yangu ni stale?".

Kujua tabaka nne, kudhibiti Data Cache kwa kila fetch (`no-store`/`revalidate`/tags), na kuakabili kwa `revalidatePath`/`revalidateTag` baada ya mabadiliko ni muhimu kupata utendaji mzuri na upya sahihi.