Transaction ni kundi la operesheni linaloshughulikiwa kama kitengo kimoja, kisichogawanyika — zote hufanikiwa pamoja (COMMIT) au zote hushindwa pamoja (ROLLBACK). Transactions huhakikisha sifa za ACID, kuhakikisha data inabaki sahihi na inayofanana hata wakati wa kushindwa au upatikanaji wa wakati mmoja.
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accounts balance balance id ;
accounts balance balance id ;
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Mfano wa kawaida: uhamishaji wa fedha. Debiti na krediti zote mbili lazima zitokee, au hakuna — vinginevyo fedha hupotea au huzalishwa. Transaction huhakikisha hili: ukikosea, ROLLBACK hubatilisha mabadiliko yote, ikiacha hifadhidata kana kwamba hakuna kilichotokea.
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)
Sifa hizi ndizo zinazofanya hifadhidata za uhusiano kuwa za kutegemewa kwa data muhimu.
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.).
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.)
Transactions na sifa za ACID ni za msingi kwa hifadhidata zinazotegemewa — ndizo zinazohakikisha data inabaki sahihi na inayofanana hata katikati ya kushindwa na upatikanaji wa wakati mmoja, ambalo ni la lazima kwa programu yoyote inayoshughulikia data muhimu, hivyo kuzielewa ni muhimu.
Thamani ya msingi ni atomicity (yote-au-hakuna): operesheni yoyote inayohusisha hatua nyingi (uhamishaji wa fedha, kuunda agizo na vipengele vya mstari, kusasisha rekodi zinazohusiana) lazima ifanikiwe kikamilifu au isifanyike kabisa — vinginevyo kushindwa katikati ya operesheni huacha hifadhidata katika hali iliyoharibika, isiyofanana (mfano wa kawaida: fedha imedebiti lakini haijakrediti).
Transactions huhakikisha hili kwa COMMIT/ROLLBACK, na kuzifanya za lazima kwa uadilifu wa data katika operesheni za hatua nyingi.
Kuelewa sifa kamili za ACID — Atomicity (yote-au-hakuna), Consistency (hali halali), Isolation (transactions za wakati mmoja haziingiliani), na Durability (mabadiliko yaliyokamilishwa hudumu wakati wa kuanguka) — huelezea kwa nini hifadhidata za uhusiano zinaaminika kwa data muhimu (fedha, maagizo, orodha ya bidhaa).
Kujua kwamba isolation hudhibiti tabia ya ufanyaji-kazi-pamoja (na isolation levels zikifanya uwiano kati ya mfanano na utendaji) huunganisha na mada za kina za concurrency.
Kwa kuwa uadilifu wa data ni muhimu kwa programu zinazotegemewa, na kwa kuwa transactions (zinazotoa atomicity na dhamana za ACID) ndiyo utaratibu unaohakikisha operesheni za hatua nyingi haziharibu data na kwamba hifadhidata inabaki inayofanana wakati wa kushindwa na concurrency, kuelewa transactions na ACID ni maarifa muhimu, ya msingi kwa kujenga programu zenye data inayotegemewa — ni nguzo ya kutegemewa kwa hifadhidata na mada muhimu ya kawaida ya mahojiano inayoonyesha uelewa wa jinsi hifadhidata zinavyohakikisha usahihi.