TransactionsBeginner
Explain ACID
“What do the four letters mean, and which mechanism provides each?”
What this tests
- Understanding each guarantee separately
Answers by level
Read the beginner answer first and notice what is missing.
Atomicity: all of a transaction or none — provided by the log and the ability to declare a transaction aborted. Consistency: declared constraints hold at commit. Isolation: concurrent transactions do not see each other’s uncommitted work — how much of committed work they see is the isolation level. Durability: once COMMIT returns, the change survives a crash — provided by fsync of the write-ahead log.
They are four separate guarantees with separate mechanisms; ask which letter someone means.
Green flags · Red flags
Strong green flag · Distinguishes database consistency from business invariants.
Green flags
- Separates the four
- Names the WAL for durability
- Knows C is about declared constraints
Red flags
- Vague "reliable"
- Conflates atomicity and durability
Follow-up questions
F1
A crash happens right after COMMIT returns but before table pages are written. Is the data safe?
Scenario
A transfer debits one account and the process dies before crediting the other. Which ACID property prevents the money vanishing, and how?