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authorChristian Grothoff <christian@grothoff.org>2016-06-20 17:40:28 +0200
committerChristian Grothoff <christian@grothoff.org>2016-06-20 17:40:28 +0200
commita8412268c057908bfd5109a8d9d605aae2375ea1 (patch)
tree276c471da4d0e12c5368d36a9039d2851e96e51f /doc
parent0fb17e2b704a591c6bd348eaf70f1c3ccbd76cc0 (diff)
downloadexchange-a8412268c057908bfd5109a8d9d605aae2375ea1.tar.gz
exchange-a8412268c057908bfd5109a8d9d605aae2375ea1.tar.bz2
exchange-a8412268c057908bfd5109a8d9d605aae2375ea1.zip
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@@ -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}