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All 5 Flashcards — Transactions and integrity
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Question
What is a transaction?
Answer
A group of statements treated as **one indivisible unit** — COMMIT makes them permanent, ROLLBACK undoes them all.
Question
What does ACID stand for?
Answer
**Atomicity** (all or none), **Consistency** (rules still hold), **Isolation** (no interference), **Durability** (survives a crash).
Question
Which property stops two withdrawals from the same balance?
Answer
**Isolation** — achieved by locking the row, so the second transaction waits and then reads the updated balance.
Question
What does durability actually require?
Answer
That the change has reached **non-volatile storage** before COMMIT returns — which is why a commit waits for the disc.
Question
What is a deadlock, and what happens?
Answer
Each transaction holds what the other wants, so neither can proceed. The database **aborts one**, which then retries.
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Full study notes for Transactions and integrity
Topic 3.3 hub
Database programming
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