You want to ensure that two concurrent transactions in PostgreSQL never see inconsistent data and avoid phantom reads. Which isolation level should you choose and why?

hard📝 Application Q15 of 15

PostgreSQL - Transactions and Concurrency

AREAD UNCOMMITTED, because it allows maximum concurrency

BREPEATABLE READ, because it prevents non-repeatable reads but allows phantoms

CREAD COMMITTED, because it is fastest and avoids dirty reads

DSERIALIZABLE, because it fully isolates transactions preventing phantoms

Step-by-Step Solution

Solution:

Step 1: Understand phantom reads and isolation levels
Phantom reads occur when new rows appear in repeated queries within a transaction.
Step 2: Match isolation level to requirement
SERIALIZABLE prevents phantom reads by fully isolating transactions, ensuring consistency.
Final Answer:
SERIALIZABLE, because it fully isolates transactions preventing phantoms -> Option D
Quick Check:
SERIALIZABLE = no phantoms, full isolation [OK]

Quick Trick: Use SERIALIZABLE to prevent phantom reads fully [OK]

Common Mistakes:

Choosing REPEATABLE READ and expecting no phantoms
Thinking READ COMMITTED prevents phantoms
Confusing READ UNCOMMITTED as safe option

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You want to ensure that two concurrent transactions in PostgreSQL never see inconsistent data and avoid phantom reads. Which isolation level should you choose and why?

Step 1: Understand phantom reads and isolation levels

Step 2: Match isolation level to requirement

Final Answer:

Quick Check:

Want More Practice?