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diff --git a/doc/paper/taler.tex b/doc/paper/taler.tex index d93cbf9cc..9e10b3937 100644 --- a/doc/paper/taler.tex +++ b/doc/paper/taler.tex @@ -32,6 +32,9 @@ \usetikzlibrary{shapes,arrows} \usetikzlibrary{positioning} \usetikzlibrary{calc} +\usepackage{caption} +\usepackage{subcaption} +\usepackage{subfig} % Relate to: % http://fc14.ifca.ai/papers/fc14_submission_124.pdf @@ -661,7 +664,7 @@ merchant trusts the exchange that issued the coin. Merchants are identified by their public key $M_p = m_s G$ which the customer's wallet learns through the merchant's webpage, which itself must be authenticated with X.509c. -% FIXME: Is this correct? +% FIXME: Is this correct? We now describe the protocol between the customer, merchant, and exchange for a transaction in which the customer spends a coin $C := (c_s, C_p)$ @@ -928,6 +931,83 @@ can then use the refresh protocol to anonymously melt the refunded coin and create a fresh coin that is unlinkable to the refunded transaction. +\section{Experimental results} + +\begin{figure}[b!] + \begin{subfigure}{0.45\columnwidth} + \includegraphics[width=\columnwidth]{bw_in.png} + \caption{Incoming traffic at the exchange, in bytes per 5 minutes.} + \label{fig:in} + \end{subfigure}\hfill + \begin{subfigure}{0.45\columnwidth} + \includegraphics[width=\columnwidth]{bw_out.png} + \caption{Outgoing traffic from the exchange, in bytes per 5 minutes.} + \label{fig:out} + \end{subfigure} + \begin{subfigure}{0.45\columnwidth} + \includegraphics[width=\columnwidth]{db_read.png} + \caption{DB read operations per second.} + \label{fig:read} + \end{subfigure} + \begin{subfigure}{0.45\columnwidth} + \includegraphics[width=\columnwidth]{db_write.png} + \caption{DB write operations per second.} + \label{fig:write} + \end{subfigure} + \begin{subfigure}{0.45\columnwidth} + \includegraphics[width=\columnwidth]{cpu_balance.png} + \caption{CPU credit balance. Hitting a balance of 0 shows the CPU is + the limiting factor.} + \label{fig:cpu} + \end{subfigure}\hfill + \begin{subfigure}{0.45\columnwidth} + \includegraphics[width=\columnwidth]{cpu_usage.png} + \caption{CPU utilization. The t2.micro instance is allowed to use 10\% of + one CPU.} + \label{fig:usage} + \end{subfigure} + \caption{Selected EC2 performance monitors for the experiment in the EC2 + (after several hours, once the system was ``warm'').} + \label{fig:ec2} +\end{figure} + +We ran the Taler exchange v0.0.2 on an Amazon EC2 t2.micro instance +(10\% of a Xeon E5-2676 at 2.4 GHz) based on Ubuntu 14.04.4 LTS, using +a db.t2.micro instance with Postgres 9.5 for the database. Using 16 +concurrent clients performing withdraw, deposit and refresh operations +we then pushed the t2.micro instance to the resource limit +(Figure~\ref{fig:cpu}) from a network with $\approx$ 160 ms latency to +the EC2 instance. At that point, the instance managed about 8 HTTP +requests per second, which roughly corresponds to one full business +transaction (as a full business transaction is expected to involve +withdrawing and depositing several coins). The network traffic was +modest at approximately 50 kbit/sec from the exchange +(Figure~\ref{fig:out}) and 160 kbit/sec to the exchange +(Figure~\ref{fig:in}). At network latencies above 10 ms, the delay +for executing a transaction is dominated by the network latency, as +local processing virtually always takes less than 10 ms. + +Database transactions are dominated by writes (Figure~\ref{fig:read} +vs. Figure~\ref{fig:write}), as Taler mostly needs to log +transactions and occasionally needs to read to guard against +double-spending. Given a database capacity of 2 TB---which should +suffice for more than one year of full transaction logs---the +described setup has a hosting cost within EC2 of approximately USD 252 +per month, or roughly 0.0001 USD per full business transaction. This +compares favorably to the $\approx$ USD 10 per business transaction +for Bitcoin and the \EUR{0.35} plus 1.9\% charged by Paypal for +domestic transfers within Germany. + +In the Amazon EC2 billing, the cost for the database (using SSD +storage) dominates the cost with more than USD 243 per month. We note +that these numbers are approximate, as the frontend and backend in our +configuration uses systems from the AWS Free Usage Tier and is not +perfectly balanced in between frontend and backend. Nevertheless, +these experimental results show that computing-related business costs +will only marginally contribute to the operational costs of the Taler +payment system. + + \section{Discussion} |