presto-main/src/main/java/io/prestosql/operator/AssignUniqueIdOperator.java/AssignUniqueIdOperatorFactory/createOperator
class AssignUniqueIdOperatorFactory:        @Override
        public Operator createOperator(DriverContext driverContext)
        {
            checkState(!closed, "Factory is already closed");

            OperatorContext operatorContext = driverContext.addOperatorContext(
                    operatorId,
                    planNodeId,
                    AssignUniqueIdOperator.class.getSimpleName());
            return new AssignUniqueIdOperator(operatorContext, valuePool);
        }