Tell about transaction isolation levels. Which ones have you worked with, and how do they differ?

Transaction isolation levels determine how much a transaction can see the changes made by other transactions and influence possible anomalies:

• Read Uncommitted: A transaction can see changes made by other transactions even if they are not yet committed. Dirty reads are possible.

• Read Committed: A transaction only sees changes that have been committed. Dirty reads are prevented, but non-repeatable reads and phantom reads can occur.

• Repeatable Read: Ensures that data read at the beginning of a transaction will not change during subsequent reads. Non-repeatable reads are prevented, but phantom reads can occur.

• Serializable: The strictest level, providing full transaction isolation as if transactions were executed sequentially. All anomalies are prevented.

In practice, most systems operate with Read Committed and Repeatable Read levels, balancing between performance and consistency.