Piye cara write concern lan read concern mengaruhi konsistensi?

Question

Accepted Answer

**Write concern** lan **read concern** ngontrol jaminan konsistensi lan durabilitas ing MongoDB (ing replica sets) — nggawe trade-off antara **performa** lan **keamanan/konsistensi**. Dheweke ngidini sampeyan nuning seberapa kuwat penulisan dikonfirmasi lan seberapa konsisten panginten, adhedhasar kabutuhan data.

## Write concern — durabilitas penulisan

```js
// write concern: how many nodes must acknowledge a write
db.orders.insertOne(doc, { writeConcern: { w: 1 } });           // primary only — fast
db.orders.insertOne(doc, { writeConcern: { w: "majority" } });   // majority of nodes — safe
db.orders.insertOne(doc, { writeConcern: { w: "majority", j: true } }); // + journaled to disk
```

```text
w: 1          → only the PRIMARY acknowledges (fast, but a write could be LOST on failover)
w: "majority" → a majority of nodes acknowledge → the write SURVIVES primary failover
               (no data loss) — safer but slower (waits for replication)
j: true       → also wait for the write to be written to the JOURNAL (disk durability)
```

**Write concern** ngontrol durabilitas: `w: "majority"` njamin penulisan direplikasi menyang mayoritas (selamet saking failover tanpa rugi) nanging luwih alon; `w: 1` luwih cepet nanging penulisan bisa ilang yen primary gagal sadurunge replikasi.

## Read concern — konsistensi panginten

```js
db.orders.find().readConcern("majority");   // read data acknowledged by a majority
```

```text
local        → returns the most recent data on the node (may not be majority-committed,
               could be rolled back) — default, fast
majority     → returns only data acknowledged by a majority (won't be rolled back) — consistent
linearizable → strongest (reflects all prior majority writes) — slowest
```

**Read concern** ngontrol data apa sing didelok panginten: `majority` mbalik mung data committen mayoritas (ora bakal dibatalke — konsisten), versus `local` (data lokal paling anyar, bisa uga durung committen mayoritas).

## Trade-off konsistensi versus performa

```text
Stronger guarantees (w: majority, readConcern: majority) → safer, consistent, but SLOWER
Weaker guarantees (w: 1, readConcern: local) → faster, but risk of data loss on failover
  or reading not-yet-durable data
→ Choose based on the data: critical data (payments) → strong; less critical → faster.
→ Reading from secondaries adds eventual-consistency considerations (stale reads).
```

## Sapa penting

Manah write concern lan read concern penting banget kanggo **ngelola trade-off konsistensi-versus-performa** ing MongoDB replica sets, mula iku pengetahuan penting senior-level kanggo mbangun MongoDB distributed applications sing bener lan tunggal apik.

Pengaturan iki ngontrol jaminan konsistensi lan durabilitas MongoDB, lan manah bakal perlu kanggo njamin data ditangani karo tingkat keamanan sing pas kanggo pentinge. **Write concern** ngerti banget penting kanggo **durabilitas**: `w: "majority"` njamin penulisan direplikasi menyang mayoritas nodes (selamet saking primary failover tanpa ilang data — kritikal kanggo data penting kaya pembayaran utawa pesanan), dene `w: 1` luwih cepet nanging beresiko ilang penulisan yen primary gagal sadurunge replikasi — trade-off sing penuh akibat dimana pilihan salah bisa nandheske ilang data senyap ing failover. **Read concern** ngontrol **konsistensi panginten**: `majority` mbalik mung data committen mayoritas (konsisten, ora bakal dibatalke) versus `local` (data paling anyar, bisa uga durung tahan lan bisa dibatalke) — pengaruhi manawa panginten bisa delok data sing mengko ilang.

Manah trade-off — jaminan luwih kuwat (majority) luwih aman lan konsisten nanging alon, dene sing luwih lemah luwih cepet nanging beresiko ilang data utawa panginten ora konsisten — lan pili adhedhasar pentinge data (kuwat kanggo data penting, cepet kanggo kurang kritikal) minangka pamilihan kunci.

Relevant uga yen maca saka secondaries nambah considerasi eventual-consistency (panginten lawas).

Amarga konsistensi lan durabilitas data kritikal (lan tingkat sing bener gumantung data), lan amarga write/read concern cara sampeyan tuning jaminan iki nglawan performa ing arsitektur MongoDB distributed (replica set), manah bakal — level durabilitas/konsistensi, trade-off performa, lan pili apik — penting senior-level pengetahuan kanggo mbangun MongoDB distributed applications bener, topik nunjuk manah trade-off consistency distributed-systems sing ngerti penting banget kanggo aplikasi dimana ilang data utawa inconsistency bakal larang biaya.