Apa iku transaksi lan properti ACID?

Question

Accepted Answer

A **transaction** iku grup operasi sing diperlakukan minangka unit tunggal, ora bisa dipecah — kabeh sukses bebarengan (`COMMIT`) utawa kabeh gagal bebarengan (`ROLLBACK`). Transaksi njamin properti **ACID**, njistiaken data tetep bener lan konsisten sanajan ana kegagalan utawa akses konkuren.

## Transaksi — kabeh-utawa-ora-apa

```sql
BEGIN;                                              -- start the transaction
  UPDATE accounts SET balance = balance - 100 WHERE id = 1;   -- debit
  UPDATE accounts SET balance = balance + 100 WHERE id = 2;   -- credit
COMMIT;                                             -- both succeed → save permanently
-- if anything fails: ROLLBACK → undo EVERYTHING (no partial transfer)
```

Contoh klasik: transfer uang. Debit lan kredit kudu kedhapataken, utawa keduanya ora — yen ora, uang ilang utawa diciptakake. Transaksi njamin iki: yen ana kesalahan, `ROLLBACK` mbatalake kabeh perubahan, ninggalake database kaya apa-apa ora anahanake.

## ACID — papat jaminan

```text
A — ATOMICITY    → all operations succeed or all fail (no partial transactions)
C — CONSISTENCY  → the database moves from one valid state to another (constraints hold)
I — ISOLATION    → concurrent transactions don't interfere (as if run sequentially)
D — DURABILITY   → once committed, changes survive crashes (persisted permanently)
```

Properti kasebut sing nggawakake relational database dipercaya kanggo data kritis.

## Kenapa atomicity penting (manfaat inti)

```text
Without transactions, a failure mid-way leaves data in an inconsistent state:
  money debited from one account but not credited to another → data corruption.
Atomicity (all-or-nothing) prevents this — the cornerstone of data integrity for
any multi-step operation (transfers, orders with line items, etc.).
```

## Isolasi lan konkurensi

```text
When many transactions run concurrently, ISOLATION controls what they can see of
each other's uncommitted changes. Isolation LEVELS (Read Committed, Repeatable Read,
Serializable) trade off consistency vs performance — higher isolation = more correct
but more locking/contention. (A deeper topic on its own.)
```

## Kenapa iki penting

Transaksi lan properti ACID minangka dasar database sing reliable — kabeh njamin data tetep bener lan konsisten sanajan ana kegagalan lan akses konkuren, sing penting kanggo aplikasi apa-apa sing nangani data penting, dadi ngerti babagan iki iku penting.

Nilai inti yaiku **atomicity** (kabeh-utawa-ora): operasi apa-apa sing melibatake pirang-pirang langkah (transfer uang, gawe pesan luwih pirang-pirang item barang, update record sing ana hubungane) kudu sukses sakabehe utawa ora — yen ora, kegagalan tengah-operasi ninggalake database ing kahanane **rusak, ora konsisten** (contoh klasik: uang dikurangi nanging ora ditambaake).

Transaksi njamin iki luwih `COMMIT`/`ROLLBACK`, nggawakake iku penting kanggo integritas data ing operasi multi-langkah.

Ngerti kabeh properti **ACID** — **Atomicity** (kabeh-utawa-ora), **Consistency** (kahanane valid), **Isolation** (transaksi konkuren ora campur), lan **Durability** (perubahan sing dikomit ngalahi kegagalan) — nerangaken kenapa relational database dipercaya kanggo data kritis (keuangan, pesan, persediaan).

Ngerti yen **isolasi** ngontrol perilaku konkurensi (luwih isolation level nggawakake trade-off konsistensi kanggo performa) hubunge luwih dalam topik konkurensi.

Sinau integritas data penting kanggo aplikasi sing reliable, lan sinau transaksi (nyediakake atomicity lan jaminan ACID) iku mekanisme sing njistiaken operasi multi-langkah ora rusak data lan database tetep konsisten ana kegagalan lan konkurensi, dadi ngerti transaksi lan ACID iku penting, pengetahuan dasar kanggo gawe aplikasi luwih reliable data — iku pokok saka reliability database lan topik interview penting, biasa sing nuduhake ngerti babagan carane database njistiaken kabenaran.