Yaya aminci na jiya sake aiki tare da Redis?

Question

IT Interview Practice · Accepted Answer

A **aminci na jiya** yana daidaita shiga ga albar wanda aka raba a gida da jingina/sabowar servers saboda a kau daya ne zai rike aminci a lokacin. Redis ana amfani da shi sau da yawa ta hanyar atomic set-if-not-exists tare da TTL — kuma yin shi daidai suke bukatawa kulawa (da fahimtar iyakoki).

## Aminci na asali Redis (SET NX tare da TTL)

```js
// acquire: SET the lock key only if it doesn't exist, with a TTL (auto-release safety)
const token = randomUUID();   // a unique token identifying THIS lock holder
const acquired = await redis.set("lock:resource", token, "NX", "EX", 30);
// NX = set only if not exists (atomic); EX 30 = auto-expire in 30s (avoid deadlock)

if (acquired) {
  try {
    // ... do the work that needs exclusive access ...
  } finally {
    // release ONLY if WE still hold it (check the token) — use a Lua script for atomicity
    await releaseLock("lock:resource", token);
  }
}
```

Aminci yana amfani da **`SET key value NX EX`**: daidai saita mabugi kawai idan babu (saboda kau daya ne aiki zai yi nasara) tare da **TTL** (saboda aminci na iyakoki idan mai rike shi ya faduwa, ikilarin dawawaita).

## Abubuwan daidaita gida biyu masu mahimmanci

```text
1. ALWAYS set a TTL → if the lock holder crashes, the lock auto-expires
   (otherwise the resource is locked forever — a deadlock)
2. Use a UNIQUE TOKEN + release only if it matches → so you don't release
   SOMEONE ELSE'S lock (e.g. if your TTL expired and another client acquired it).
   Release must be ATOMIC (check-token-then-delete via a Lua script).
```

```lua
-- safe release: delete only if the value matches our token (atomic via Lua)
if redis.call("get", KEYS[1]) == ARGV[1] then return redis.call("del", KEYS[1]) else return 0 end
```

## Iyakoki da Redlock

```text
⚠️ A single-Redis lock isn't perfectly safe: if the TTL expires mid-work, or with
   failover (the lock not yet replicated), two clients could both hold it.
→ REDLOCK algorithm → acquire the lock across MULTIPLE independent Redis nodes
   (majority) for stronger guarantees (though even Redlock is debated).
→ For critical correctness, combine with fencing tokens or use a system designed for
   consensus (e.g. ZooKeeper/etcd). Know the trade-offs.
```

## Me ya sa ya mahalaci

Fahimtar aminci na jiya tare da Redis yana da mahimmanci don **daidaita shiga ga albarru wanda aka raba** a cikin aminci jiya, saboda ya zama ilimi mai amfani — da fahimtar iyakoki na daidaita sune mahimmanci.

Aminci na jiya yana magance pangangare na gaske: tabbatarwa cewa aiki/sabowar gida ɗaya kawai zai aiwata mataki mai mahimmanci a lokacin (ikilarin maimakon aiki, gida masu jiya akan albarru wanda aka raba, ko aika masu sabani) a tsarin multi-server, kuma Redis wani kayan na gida.

Fahimtar **hanyar asali** — `SET key value NX EX` (atomic set-if-not-exists tare da TTL) saboda kau daya ne aiki zai sami aminci kuma iyakoki a rike idan faduwa — shi ne ilimi na tushe.

Bisa mahimmanci, fahimtar **abubuwan daidaita gida biyu** yana mahimmanci: **koda da hankali amfani da TTL** (saboda rike aminci na mai faduwa iyakoki, ikilarin dawawaita da kuwa) da **amfani da jiya ne sama-sama da daidaita** (saboda ba za ka yi daidaita aminci na aiki ne idan TTL ya iyakoki — tare da atomic duba-sai delete ta Lua script).

Wannan abubuwan ne nabin da sauran ilimi suna da ƙankunan ama masu cutarwa.

Daidai mahimmanci ne fahimtar **iyakoki**: aminci na Redis ɗaya ba shi cikakke aminci ba (iyakoki na TTL a tsakanin aiki ko sauya zai ba aiki biyu tunanin aminci), wanda ya haifar da **Redlock** algorism (samuwa a gida da jingina da yawa na Redis) don tabbatarwa mafi karfi — da fahimtar cewa don daidaita mahimmanci, alamar fencing ko tsarin ijma (ZooKeeper/etcd) kuma zai bukatawa.

Wannan fahimta na cinikare da iyakoki ta nuna fahimta mai matshewa.

Tun da daidaita shiga albarru wanda aka raba a tsarin jiya ya bukatawa gaske, kuma tun da aminci jiya na Redis sune gida kuma sune bukatawa kulawa daidaita (TTL, jiya ne sama-sama, atomic daidaita) da fahimtar iyakoki (Redlock, halifar faduwa), fahimtar aminci na jiya tare da Redis — hanyar, abubuwan daidaita gida, da iyakoki — yana mahimmanci, ilimi mai amfani na gaske don daidaita jiya, jaji ne inda fahimtar faduwa da cinikare kuwa suna mahimmanci kamar hanyar asali.

Aminci na asali Redis (SET NX tare da TTL)

Abubuwan daidaita gida biyu masu mahimmanci

Iyakoki da Redlock

Me ya sa ya mahalaci

Tambayoyi masu alaƙa