Transaction yana haɗa statements zuwa raka'a ɗaya mai atomic: ko dukansu sun commit ko dukansu sun roll back, yana ba da A, C, I, D na ACID. Isolation level yana daidaita "I" — nawa transactions na lokaci guda za su iya gani na bayanan juna waɗanda ba a commit ba ko masu canzawa.
| Matakin | Dirty read | Non-repeatable read | Phantom |
|---|
| READ UNCOMMITTED | mai yiwuwa | mai yiwuwa | mai yiwuwa |
| READ COMMITTED | a'a | mai yiwuwa | mai yiwuwa |
| REPEATABLE READ (tsohon InnoDB) | a'a | a'a | galibi a'a* |
| SERIALIZABLE | a'a | a'a | a'a |
*REPEATABLE READ na InnoDB yana amfani da MVCC (kowace transaction tana karanta snapshot mai daidaici) tare da next-key locks, don haka yana toshe yawancin phantoms kuma — mai ƙarfi fiye da yadda ma'aunin SQL ke buƙata.
SELECT @@transaction_isolation; -- REPEATABLE-READ by default
START TRANSACTION;
SELECT balance FROM accounts WHERE id = 1; -- snapshot taken here
UPDATE accounts SET balance = balance - 100 WHERE id = 1;
UPDATE accounts SET balance = balance + 100 WHERE id = 2;
COMMIT; -- both updates apply, or ROLLBACK undoes both
Riƙe tsohon InnoDB (REPEATABLE READ) sai dai kana da dalili. READ COMMITTED (abin da Postgres/Oracle ke tsoho a kai) yana rage takara na locks ga tsarin da ke rubuta da yawa; SERIALIZABLE daidai ne amma yana serialize aikin da ke karo kuma yana iya yin deadlock sosai.
Isolation shine dial tsakanin daidaito da concurrency. Fahimtar waɗannan matsaloli yana ba ka damar bayyana kwari kamar "jimlar bai daidaita ba a lokacin load" da zaɓen matakin da ke sa transactions masu motsa kuɗi su zama daidai ba tare da ƙuntata throughput ba tare da larura ba.
Ɗakin karatu na tambayoyin hira na IT tare da amsoshi cikakke — daga Junior zuwa Senior.
Ba da Gudummawa