What is the default transaction isolation level in Oracle?

Oracle supports the following transaction isolation levels:

• READ COMMITTED (default)
• SERIALIZABLE
• READ ONLY

The default level in Oracle is READ COMMITTED. This means that each read operation sees only the data that was committed at the start of the read. Non-repeatable reads are possible, but dirty reads are not allowed.

Example:

SET TRANSACTION ISOLATION LEVEL READ COMMITTED;
-- or simply use the default behavior

The SERIALIZABLE level provides stricter isolation, preventing non-repeatable reads, but may lead to locking and reduced performance.