Oracle SQL Oracle SQL Transactions and Concurrency Control 3

Question 1

What is the default transaction isolation level in Oracle Database?

Accepted Answer

READ COMMITTED

Answer

SERIALIZABLE

Answer

READ UNCOMMITTED

Answer

REPEATABLE READ

Question 2

Which read phenomenon is prevented by Oracle's READ COMMITTED isolation level?

Accepted Answer

Dirty reads

Answer

Non-repeatable reads

Answer

Phantom reads

Answer

Lost updates

Question 3

What does a dirty read mean in the context of database transactions?

Accepted Answer

Reading uncommitted data from another transaction that may later be rolled back

Answer

Reading data that has been physically deleted from the database

Answer

Reading data that contains encoding or character set errors

Answer

Reading data from a table with corrupted indexes

Question 4

Which Oracle SQL statement correctly sets the current transaction's isolation level to SERIALIZABLE?

Accepted Answer

SET TRANSACTION ISOLATION LEVEL SERIALIZABLE

Answer

ALTER SESSION SET ISOLATION_LEVEL = SERIALIZABLE

Answer

ALTER TRANSACTION SET LEVEL SERIALIZABLE

Answer

SET SESSION ISOLATION LEVEL SERIALIZABLE

Question 5

What is a phantom read in the context of database transactions?

Accepted Answer

A transaction re-executes a range query and finds new rows inserted and committed by another transaction since the first execution

Answer

Reading a row that was physically deleted but still appears in the buffer cache

Answer

Reading the same single row twice and getting different column values each time

Answer

A read operation that takes an unexpectedly long time due to lock contention

Question 6

What does SET TRANSACTION READ ONLY accomplish in Oracle SQL?

Accepted Answer

Starts a transaction that can only SELECT and sees a consistent data snapshot as of the transaction start time

Answer

Makes all tables in the current session permanently read-only

Answer

Prevents any DDL operations for the lifetime of the current session

Answer

Sets the entire database instance to read-only mode for maintenance

Question 7

What is the primary purpose of the UNDO tablespace in Oracle in relation to transactions?

Accepted Answer

To store before-images of changed data, enabling ROLLBACK operations and read-consistent snapshots

Answer

To store redo log files used for database recovery after a crash

Answer

To permanently archive all committed transaction data for auditing

Answer

To store the SQL text of every statement executed in each transaction