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%
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\title{Node.js characteristics and comparison with other \\backend technologies}


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	Nenad Mišić, nenad.misic997@gmail.com\\
    Nikola Nemeš, nikolanemzi@gmail.com}
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University of Novi Sad}}

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\begin{abstract}
The abstract goes here.

Keywords --- node.js; performance; backend technologies;
\end{abstract}





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\section{Introduction}
% no \IEEEPARstart
In this paper, we will compare Node.js to other popular backend technologies in terms of performance and scalability by analyzing different aspects of their implementations. We will further explain the key differences which allow Node.js to outperform its alternatives in specific situations. We will also address situations in which Node.js falls behind.\\ This paper can help people make a better decision which technology to use according to the project needs. In addition, it highlights the subtle differences which are often overlooked by developers and shows them what are the tasks in which this technology excels, but also presents critical situations where it is not the best choice.\\

%\hfill mds
%\hfill August 26, 2015
\section{Introduction to node.js}
In this part we will go over a brief historical summary of
Node.js and describe the basic principles, including:
\begin{itemize}
	\item Asynchronous function handling
	\item Event pooling
	\item Single-threaded pattern
\end{itemize}
\subsection{Historical overview}
Here we will describe the idea and process of turning a
frontend language into a fully-functional and high-performing
server runtime environment.\\

Node.js was developed by Ryan Dahl in 2009. It was built on Google's V8 JavaScript engine, which was formerly only used for front end applications in Google Chrome and couple of other internet browsers. It was initially only supported on Linux and Mac OS systems. The reason for the development of node.js was that the most popular web servers(such as Apache) had certain limitations. The biggest one was handling handling a large number of concurrent requests(up to 10000 and more). \cite{presentation:dahl}

The main idea was to make a server side technology that could scale better and serve a larger number of clients. This was accomplished by using asynchronous function calls instead of long running synchronous function calls. This enables the server to make better use of processor time, but it also comes with its challenges when writing code.

A node package manager(npm) was introduced in 2010, which has allowed the developers to easily distribute modules. This has led to a far greater speed of development of node.js projects.\cite{npm}

\subsection{Basics of Node.js}
In this subsection we will go over the basic principles which set Node
apart from other backend technologies. \\

%TODO: mozda dodaj za runtime environment
\subsubsection{Asynchronous function handling}
Node.js uses asynchronous function handling for I/O functions. What this means is that when an I/O function is called, the calling thread(the main thread of node.js) will not wait for it to finish execution. Instead it can continue to run the rest of the program that is not dependent on the result of the I/O operation. The code that is dependent on the result of the I/O operation will be placed in a callback function. This function will be called once the I/O operation is finished. The execution of the asynchronous method is usually delegated to the system kernel or a database program.
\begin{figure}[ht]
	\centering
	\includegraphics[width=0.9\linewidth]{asynchronous}
	\caption{Asynchronous function calls}
	\label{fig:asynchronous}
\end{figure}

\subsubsection{Event pooling}
\begin{figure}[ht]
	\centering
	\includegraphics[width=0.9\linewidth]{eventpool}
	\caption{Event loop}
	\label{fig:eventpool}
\end{figure}
The event loop allows Node.js to perform asynchronous I/O operations. \cite{eventloop:nodejs} It goes through a couple of phases. Each phase contains a queue of callbacks. Each phase also has a set of actions specific to it.\\


Figure \ref{fig:eventpool} shows a diagram of the node js event loop. Every rectangle on the figure represents one phase of the event loop. In the next set of subsections, each phase will be analyzed. \cite{eventloop:nodejs}
\paragraph{Timers}
	Callbacks from the setTimeout method will be placed in the timers phase's queue. This JavaScript method is used to specify a time period after which the callback function should be called. But since the event loop goes through multiple phases of variable lengths\footnote{In order to stop a phase from running too long and delaying other phases, a time limit is imposed on the length of the phase}, it can not be guaranteed that the callback function will be executed after that exact time interval, but rather after the timer expires.
\paragraph{Pending callbacks}
	The callbacks which need to be executed in the next iteration of the event loop are put in this phase's queue. For instance, callbacks for some types of errors need to wait to report the error.
\paragraph{Poll}
	Most callbacks used by the developer will end up in the poll phase's queue. That is because, once the system kernel finishes with the I/O operation, it puts the callback into this queue. If there are no callbacks ready in this phase, the event loop will block the execution and wait for a certain amount of time before continuing(unless there are callbacks ready in the check phase's queue or there are timer callbacks ready to execute). It does that because during that time, some callbacks might be added to the queue. The developer can avoid this feature if needed by using the setImmediate method. This method places a callback function in the check phase's queue. If both the poll and check phase's queues are empty, and there are callbacks in the timer phase's queue ready, the event loop will go back to the timer phase in order to accomplish a more precise execution of the setTimeout method.
\paragraph{Check}
	The check phase contains the higher priority callbacks. If there is a situation where the poll phase has no callbacks ready, and timer and check phases both have ready callbacks, the event loop will prioritize the callbacks from the check queue.
\paragraph{Close}
	In this phase, the event loop will handle the callbacks of abruptly closed sockets or streams. If the stream closes normally, the callback will be executed via the nextTick method.


The nextTick method allows the user to bypass the event loop. It executes the callback given to it at the end of the currently executed operation\footnote{In this case an operation is defined as a transition between the JavaScript and V8 engine's native code.}.

\subsubsection{Single-threaded pattern}
Unlike most other server side technologies, a Node.js program is single-threaded. This is made possible by using the event loop in combination with asynchronous I/O operations. This frees up the processor more than Node.js's multi-threaded alternatives.


\section{Performance comparison}
In this part we will go into detail about differences in
technologies that affect performance and analyze concrete
results in different environments. The technologies against which Node.js will be compared are Python-web and PHP\cite{performance:lei} in the first part, and Apache and EventMachine, an evented Ruby web server\cite{performance:mccune} in the second part of this section.
\subsection{Reasons behind the differences}
The main reasons for the differences in performance are that Node.js uses asynchronous I/O function calls and that Node.js is a single-threaded web technology, unlike most of the popular alternatives.
\subsubsection{Single-threaded versus Multi-threaded client serving}
In this subsection we will go over how the server handles client requests depending on the fact whether it is single-threaded or multi-threaded and how it affects server performance.
\paragraph{Single-threaded}
The servers main thread has to serve each client. But that same thread also has to listen for incoming requests from other clients and put them in a queue. Because of this, if there are many requests coming to the server, a client can wait for a long time before the server is available. Especially problematic are the requests that take a long time to finish, because the server is unavailable to other clients. The server has to find a way to get around these issues and be fair to all of it's clients.
\paragraph{Multi-threaded}
In this case, the server's main thread's only duty is to listen to incoming requests from the clients. Once the request comes, the server spawns a new thread to take care of it. Like this, multiple clients can be served by the server at the same time. The problem that comes with this approach is that spawning and managing threads is costly for the processor and therefore has a negative effect on the performance. Other than that, another issue is that there is a limited number of threads that can run efficiently at the same time. Therefore, if there are too many clients, a multi-threaded server will not be much faster than a single-threaded one.


\subsubsection{Synchronous versus Asynchronous I/O operations}
In this subsection we will go over how the server handles I/O operations depending on whether the technology is synchronous or asynchronous and what effect that has on server performance.
\begin{figure}[ht]
	\centering
	\includegraphics[width=0.9\linewidth]{synchronous_versus_asynchronous}
	\caption{Synchronous versus asynchronous programming}
	\label{fig:synchronousversusasynchronous}
\end{figure}
\paragraph{Synchronous}
In synchronous handling of I/O operations, the thread that serves the client gets blocked until the I/O operation finishes. The issue is that during that time, the server thread can not be used for anything else\ref{fig:synchronousversusasynchronous}. The processor can switch to another thread(if the server is multi-threaded), but the transition also requires some time. This can also be problematic because most requests include some I/O operations.
\paragraph{Asynchronous}
When it comes to asynchronous I/O operations, the calling thread will not wait for the I/O operation to finish\ref{fig:synchronousversusasynchronous}, but rather execute other operations that are not dependent on the I/O function finishing. This can have a positive effect on the server performance.

Node.js combines the single-threaded approach with asynchronous I/O function calls. By doing this, it maximizes efficiency in serving a large number of clients. It is especially good if the requests are data intensive, but it has drawbacks when the requests are computationally heavy.
\subsection{Node.js against Python-web and PHP}
In this section, we will analyze how Node.js compares to Python-web and PHP. This section will heavily rely on experiments performed and described in a related work\cite{performance:lei}. The experiments go over a couple of different server benchmark tests. it simulates 10000 requests from each client, and the number of clients change between 10, 100, 200, 500, and 1000. The first experiment will be a regular stress test, the second one will be a computational intensive test and the third one will be an I/O intensive test.
\subsubsection{Regular stress test}
In this test clients send requests, and the server responds only with a "Hello world" string. This is neither I/O intensive nor computational intensive, but it tests how well the server runtime handles a large number of requests. Figures \ref{fig:resultsstress1} and \ref{fig:resultsstress2} show the results of the test. Figure \ref{fig:resultsstress1} shows how many requests per second the server can handle depending on the number of users that are sending these requests. A trending can be seen that each server's performance improves with the increasing number of users, up until some point, after which it decreases. The results show that Node.js can handle the largest number of requests out of the three technologies used. It also does not lose it's performance as drastically as PHP when the number of users increases. Figure \ref{fig:resultsstress2} shows how much time it takes the server to respond to user requests. It can be noticed that Node.js outperforms its alternatives in this regard too. Once again, PHP's performance decreases rapidly with the increasing number of users. Python-web is fine in this aspect, but it is still lacking compared to Node.js. The conclusion here is that Node.js handles the regular stress test the best.
\begin{figure}[ht]
	\centering
	\includegraphics[width=0.9\linewidth]{results1}
	\caption{Results of the regular stress test, mean requests per second in relation to client count\cite{performance:lei}}
	\label{fig:resultsstress1}
\end{figure}
\begin{figure}[ht]
	\centering
	\includegraphics[width=0.9\linewidth]{results2}
	\caption{Results of the regular stress test, time needed for server to respond in relation to client coun\cite{performance:lei}t}
	\label{fig:resultsstress2}
\end{figure}


\subsubsection{CPU intensive test}
In this test clients send requests, and the server has to calculate the tenth number of the Fibonnaci Sequence and return it as the result. This request is computationally heavy, since the server has to do a lot of calculating all over again for each request. Figures \ref{fig:resultscpu1} and \ref{fig:resultscpu2} show the results of the test. Figure \ref{fig:resultscpu1} shows how many requests per second the server can handle depending on the number of users that are sending these requests. Figure \ref{fig:resultscpu2} shows how much time it takes the server to respond to user requests. The results shown are very similar to the ones from the regular stress test, but with some differences. Once again, Node.js is better than the other two when the number of users is over 200. But at a lower number of users, PHP outperforms Node.js in terms of both of the criteria. There have also been tests for the twentieth and thirtieth Fibonnaci number, in order to further explore this type of test. The results show that each technology falls off drastically, as the Fibonnaci


\begin{figure}[ht]
	\centering
	\includegraphics[width=0.9\linewidth]{results3}
	\caption{Results of the CPU intesive test, mean requests per second in relation to client count\cite{performance:lei}}
	\label{fig:resultscpu1}
\end{figure}
\begin{figure}[ht]
	\centering
	\includegraphics[width=0.9\linewidth]{results4}
	\caption{Results of the regular stress test, time needed for server to respond in relation to client count\cite{performance:lei}}
	\label{fig:resultscpu2}
\end{figure}

\subsubsection{Static contents delivery test}
\subsubsection{IO intensive test}

\section{Scalability comparison}
In this part we will go into detail about differences in
technologies that affect scalability and describe the key features
of Node that make it easily scalable.
\subsection{Reasons behind the differences}
\subsection{“Horizontal scaling” on a single machine}
\subsection{Node clustering}
\subsection{NoSQL databases and eventual consistency}

\section{Drawback of using node.js}
In this part we will go into detail about differences in
technologies that affect server security, code readability and
reusability etc.
\subsection{Single-threaded pattern flaws}
\subsection{Why Node is not used in enterprise}
\subsection{Security flaws caused by performance}
\subsection{Synchronization problems because of eventual consistency}

\section{Results and discussions}

\section{Conclusion}


\begin{thebibliography}{1}

\bibitem{node_basic:tilkov}
	Tilkov, S., \& Vinoski, S. (2010). Node. js: Using JavaScript to build high-performance network programs. IEEE Internet Computing, 14(6), 80-83.\\
	This paper serves as a good starting point to get introduced to Node.js. It goes over the basics of how Node works and the pros and cons of event driven programming.

\bibitem{performance:lei}
	Lei, K., Ma, Y., \& Tan, Z. (2014, December). Performance comparison and evaluation of web development technologies in php, python, and node. js. In 2014 IEEE 17th international conference on computational science and engineering (pp. 661-668). IEEE.\\
	This paper goes deeply into performance analysis and comparison between Node.js and two other popular backend technologies. It graphically presents the results gathered in different tests performed over those platforms and it is a great head start for research.
\bibitem{security:ojamaa}
	Ojamaa, A., \& Düüna, K. (2012, December). Assessing the security of Node. js platform. In 2012 International Conference for Internet Technology and Secured Transactions (pp. 348-355). IEEE.
	This paper goes over security pitfalls of the Node.js platform. It contains an explanation of Node.js advantages too, but it is mainly about the many flaws that come with using a frontend language and a technology that does not emphasize security to write server logic. It also gives two ways to cause denial of service in Node.js servers that have been undocumented before.
\bibitem{presentation:dahl}
	Dahl, R., (2009, November 8) node.js\\Retrieved from\\ \url{https://www.slideshare.net/AartiParikh/original-slides-from-ryan-dahls-nodejs-intro-talk}\\
	This is the original presentation on node.js given by its creator Ryan Dahl.

\bibitem{npm}
	Npm. (2010). Retrieved from \url{https://www.npmjs.com/}
	This is the official site for the node package manager, npm.

\bibitem{eventloop:nodejs}
	Node js documentation. Retrieved from \url{https://nodejs.org/en/docs/guides/event-loop-timers-and-nexttick/}
	This is the official node js documentation.

\bibitem{performance:mccune} McCune, R. R. (2011). Node. js paradigms and benchmarks. Striegel, Grad Os F, 11, 86.
	In this paper, Node.js is compared to Apache and EventMachine web technologies in terms of performance.
\end{thebibliography}




% that's all folks
\end{document}


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