Menene idempotency, kuma yaya idempotency keys ke sa retries su zama masu aminci?

Question

IT Interview Practice · Accepted Answer

**Idempotency** yana nufin yin aiki **sau da yawa yana da tasiri iri ɗaya da yin sa sau ɗaya**. Yana da muhimmanci domin networks ba abin dogaro ba ne: idan client ya aika request kuma response bai taɓa zuwa ba, ba zai iya sanin ko server ya sarrafa shi ba. Idan ya sake gwadawa, aikin da ba idempotent zai iya gudana sau biyu.

## Matsalar

```text
Client ──POST /payments {$100}──▶ Server   (charges $100 ✓)
Client ◀────────X (timeout)────── Server   (response lost)
Client ──POST /payments {$100}──▶ Server   (charges $100 AGAIN ✗ → $200!)
```

`GET`, `PUT`, da `DELETE` a dabi'ance idempotent ne, don haka sake gwada su yana da aminci. `POST` **ba haka ba** — nan ne ainihin inda cajin kwafi da orders kwafi ke fitowa.

## Mafita: idempotency keys

Client yana samar da **key na musamman** (yawanci UUID) ga aikin na hankali kuma yana aika shi a cikin header. Server yana adana key tare da sakamako; idan key iri ɗaya ya sake zuwa, yana mayar da sakamako **da aka adana** maimakon sake zartarwa.

```http
POST /payments HTTP/1.1
Idempotency-Key: 5f2b8c1e-3a4d-4e6f-9c0b-1a2b3c4d5e6f
Content-Type: application/json

{ "amount": 100, "currency": "usd" }
```

```text
Server logic on receiving a request with an Idempotency-Key:
  1. Look up the key in a store (e.g. Redis/DB).
  2. If found → return the saved response (no re-charge).      ← the retry case
  3. If not  → process, save (key → response), then return.
  (Wrap 3 in a transaction / lock so concurrent retries don't double-execute.)
```

**Key iri ɗaya** a retry yana ba da `200` iri ɗaya da payment iri ɗaya — an caje abokin ciniki sau ɗaya. Haka nan API na Stripe ke aiki daidai.

## Me ya sa yake da muhimmanci

Wannan tambaya tana rarrabe injiniyoyin da ke ƙira don happy path da waɗanda ke ƙira don **gazawa**, wanda shi ne ainihin abin da dogaro na production ya shafa. Tsarukan da aka rarraba (distributed) suna ba da tabbacin cewa timeouts da gazawa na ɓangare *za su* faru, don haka kowane endpoint mai side effects — payments, orders, aika kuɗi — yana bukatar dabarar retry, kuma "kawai sake gwadawa" yana da haɗari ga `POST`. Mai hira yana son jin fahimtar sassa biyu: na farko, cewa idempotency wani hali ne da za ka iya *ƙira a ciki* (sa `PUT`/`DELETE` su zama masu aminci a dabi'ance, da ba `POST` **idempotency key** idan ba zai iya ba), na biyu, cikakken bayanin concurrency mai dabara — retries biyu da suka zo lokaci guda kada duka biyu su zartar, don haka duban key da rubutu suna bukatar lock ko unique constraint. Yin wannan daidai shi ne bambanci tsakanin caje abokin ciniki sau ɗaya da caje shi sau biyu, shi ya sa kowane API mai muhimmanci na payments da kasuwanci ke aiwatar da shi.

Matsalar

Mafita: idempotency keys

Me ya sa yake da muhimmanci

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