Transactions hufanya kazi vipi katika MongoDB?

Question

Accepted Answer

MongoDB inaunga mkono **multi-document ACID transactions** (tangu v4.0 kwa replica sets, v4.2 kwa sharded clusters) — kuweka operesheni pamoja katika nyaraka/collections nyingi ili zote zifanikiwe au zote zishindwe. Hata hivyo, muundo wa nyaraka wa MongoDB mara nyingi hufanya transactions *zisihitajike* kupitia operesheni za atomiki za nyaraka moja.

## Operesheni za nyaraka moja tayari ni za atomiki

```text
KEY POINT: operations on a SINGLE document are ALWAYS atomic in MongoDB.
→ Because related data is often EMBEDDED in one document, many operations that would
  need a transaction in SQL are a single atomic document update in MongoDB.
→ Good schema design (embedding) often eliminates the NEED for multi-doc transactions.
```

```js
// updating a document and its embedded array atomically — NO transaction needed
db.accounts.updateOne(
  { _id: id },
  { $inc: { balance: -100 }, $push: { transactions: { amount: -100 } } }
);  // atomic — both changes succeed or fail together (single document)
```

## Multi-document transactions (zinapohitajika kweli)

```js
// for operations across MULTIPLE documents/collections that must be atomic
const session = db.getMongo().startSession();
session.startTransaction();
try {
  db.accounts.updateOne({ _id: 1 }, { $inc: { balance: -100 } }, { session });
  db.accounts.updateOne({ _id: 2 }, { $inc: { balance: 100 } }, { session });
  session.commitTransaction();        // both succeed together
} catch (e) {
  session.abortTransaction();          // or both roll back
} finally {
  session.endSession();
}
```

Multi-document transactions (zikitumia session) hutoa dhamana za ACID katika nyaraka — kwa hali kama kuhamisha kati ya nyaraka tofauti za akaunti.

## Tumia transactions kwa uchache

```text
✓ Transactions are available and provide ACID across documents WHEN NEEDED
✗ But they have PERFORMANCE COSTS (overhead, locking) — don't overuse them
→ PREFER good schema design (embedding related data) so single-document atomic
  operations suffice. Use multi-document transactions only when data genuinely
  spans documents and must be consistent (e.g. money transfers between accounts).
→ Requires a replica set (not standalone).
```

## Kwa nini ni muhimu

Kuelewa transactions za MongoDB — na muhimu zaidi wakati zinapohitajika — ni muhimu kwa kuhakikisha uthabiti wa data katika programu za MongoDB, hivyo ni maarifa ya thamani kwa kujenga mifumo sahihi.

Ufahamu muhimu zaidi ni kwamba **operesheni za nyaraka moja ni za atomiki kila wakati** katika MongoDB, na kwa sababu muundo wa nyaraka unahimiza **kupachika data inayohusiana katika nyaraka moja**, operesheni nyingi ambazo zingehitaji transaction katika relational database (ambapo data inayohusiana imegawanywa katika tables) ni **sasisho moja la atomiki la nyaraka** katika MongoDB — hivyo **ubunifu mzuri wa schema mara nyingi huondoa hitaji la multi-document transactions**.

Hili ni jambo muhimu la kidhana: atomiki-kwa-kila-nyaraka ya MongoDB, ikichanganywa na kupachika, hushughulikia mahitaji mengi ya uthabiti bila transactions.

Kuelewa kwamba MongoDB **inaunga mkono multi-document ACID transactions** (tangu v4.0+) kwa hali ambapo operesheni kweli zinapita katika nyaraka/collections nyingi (kama kuhamisha kati ya nyaraka tofauti za akaunti) ni muhimu — zinapatikana zinapohitajika kweli, zikitoa dhamana za yote-au-bila-kitu.

Muhimu vile vile ni mwongozo wa **kutumia transactions kwa uchache**: zina gharama za utendaji (overhead, locking), hivyo njia inayopendekezwa ni ubunifu mzuri wa schema (kupachika) ili operesheni za atomiki za nyaraka moja zitoshe, zikiacha multi-document transactions kwa mahitaji halisi ya uthabiti wa nyaraka-mbalimbali.

Kuelewa hili — atomiki ya nyaraka moja, kwamba kupachika mara nyingi huondoa hitaji la transactions, kwamba multi-document transactions zipo kwa wakati zinapohitajika kweli, na upendeleo wa ubunifu kuliko transactions — kunaonyesha uamuzi madhubuti wa MongoDB.

Kwa kuwa uthabiti wa data ni muhimu na njia ya MongoDB (atomiki ya nyaraka + transactions za hiari) inatofautiana na muundo unaozingatia transaction wa SQL, kuelewa transactions za MongoDB — hasa kwamba operesheni za nyaraka moja ni za atomiki, kupachika hupunguza mahitaji ya transactions, na multi-document transactions zinapatikana lakini zinapaswa kutumiwa kwa busara — ni maarifa ya thamani na muhimu kwa kuhakikisha uthabiti kwa usahihi na ufanisi katika programu za MongoDB, mada inayoonyesha uelewa wa muundo wa uthabiti wa MongoDB na mazoea mazuri ya ubunifu.