Isolation Levels

Preview — 3 of 10 questions

What anomaly can occur at the READ UNCOMMITTED isolation level that no other level allows?

APhantom reads — new rows appear in repeated range queries

BNon-repeatable reads — the same row returns different values within one transaction

CSerialization failures — the transaction is aborted due to a conflict

DDirty reads — reading data from another transaction that has not yet committed and may be rolled back

At the READ COMMITTED isolation level, which anomaly is prevented and which one can still occur?

APrevents dirty reads; still allows non-repeatable reads

BPrevents phantom reads; still allows dirty reads

CPrevents both dirty reads and non-repeatable reads; only phantom reads can still occur

DPrevents all anomalies — equivalent to SERIALIZABLE in practice

Which anomaly is specifically addressed by REPEATABLE READ that READ COMMITTED does not prevent?

ADirty reads — reading uncommitted data from other transactions

BNon-repeatable reads — the same row returning different values within one transaction

CPhantom reads — new rows appearing in repeated range queries

DSerialization failures — transactions being aborted due to write conflicts

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