Can you explain what the isolation level in a transactional database means?

The isolation level in a transactional database determines how isolated a transaction is from changes made by other transactions. It affects data visibility and prevents issues such as:

• Dirty Read: Reading data that has been modified but not yet committed by another transaction.
• Non-repeatable Read: When data read at the beginning of a transaction is modified by another transaction before the first transaction completes.
• Phantom Read: The appearance of new rows that match the query condition during a transaction.

Main isolation levels:

• Read Uncommitted: The lowest level, allows dirty reads.
• Read Committed: Prevents dirty reads but allows non-repeatable reads.
• Repeatable Read: Prevents dirty and non-repeatable reads but allows phantom reads.
• Serializable: The strictest level, provides full transaction isolation, preventing all the issues listed.

Choosing an isolation level is a trade-off between performance and data integrity.