How does the system react if a failure or exception occurs during a transaction?

If a failure or exception occurs during a transaction in the system, all changes made within that transaction are usually rolled back. This guarantees that the database or system remains in a consistent state and does not contain partially applied changes.

For example, in Java, using transactions (such as through JDBC or Spring), when an exception occurs, the transaction is marked as unsuccessful, and a rollback is triggered:

try {
    connection.setAutoCommit(false);
    // database operations
    connection.commit();
} catch (SQLException e) {
    connection.rollback(); // rollback changes
}

Thus, the system ensures atomicity of operations: either all changes are applied, or none are.