CompTIA DataSys+ (DS0-001)Database Management and MaintenanceHard
A database administrator is setting up a new database server and needs to configure the appropriate `isolation level` for transactions. The primary concern is to ensure that transactions can read data that has been modified by other concurrent transactions but not yet committed, to avoid blocking and improve concurrency for certain analytical reports. However, they are aware this might lead to reading 'dirty' data. Which SQL standard isolation level allows this behavior?
- ASERIALIZABLE
- BREPEATABLE READ
- CREAD COMMITTED
- DREAD UNCOMMITTED
Show answer & explanationAnswer & explanation
Correct answer: D. READ UNCOMMITTED
READ UNCOMMITTED isolation level allows transactions to read data that has been modified by other transactions but not yet committed (dirty reads). This maximizes concurrency but sacrifices data consistency, which aligns with the scenario's requirement to avoid blocking for analytical reports while accepting 'dirty' data.
Why the other options are wrong
- A. SERIALIZABLE is the highest isolation level, ensuring transactions execute as if in serial, preventing all concurrency anomalies (dirty reads, non-repeatable reads, phantom reads), but significantly reduces concurrency.
- B. REPEATABLE READ prevents dirty reads and non-repeatable reads (a transaction sees the same data if re-read), but allows phantom reads. It does not allow reading uncommitted data.
- C. READ COMMITTED prevents dirty reads (only committed data is visible), but allows non-repeatable reads and phantom reads. It does not allow reading uncommitted data.
Isolation Level (READ UNCOMMITTED)
The lowest SQL standard isolation level, allowing transactions to read uncommitted changes made by other concurrent transactions, leading to 'dirty reads' but maximizing concurrency.
- Permits dirty reads, non-repeatable reads, and phantom reads.
- Offers the highest concurrency but the least data consistency.
- Suitable for scenarios where approximate data is acceptable and blocking must be avoided.
Memory trick: Isolation levels are like privacy settings for your data reads.