|Web Cluster Laboratory|
The hardware in our Web Cluster Laboratory is composed of
commodity PC hardware and equipped with additional measurement
infrastructure for performance evaluation.
PCs with cheap off-the-shelf components are interconnected
using a fast-/gigabit ethernet switch.
We use Open Source solutions for the operating systems
and all other software needed. The system is used as a
distributed web server serving both static and dynamic
content. The dynamic generation of web pages includes
on-demand generation of HTML pages from XML documents
using XSL, and a full-featured e-commerce system, which
consists of an Enterprise Java Beans implementation of
a bookshop as specified by the TPC-W benchmark.
The measurement infrastructure is composed of several
GPS receiver cards connected to a roof-mounted GPS antenna.
For time synchronization, we use a combination of NTP
and the PPS API, where our GPS receivers generate precise
pulses marking the start of every second.
We use additional hardware to connect
the PPS pulse to every node of the cluster.
A kernel buffer is used to record time stamps for
relevant events inside the kernel during the
Buffering the kernel time stamps enables us to conduct
measurements with high data volume and microsecond precision.
Additionally, we record time stamps for important
events in user-space processes and measure the ressource
The use of an external clock for measuring the
interrupt lantency for every PPS pulse and correcting the
time stamps used by NTP afterwards has been evaluated and
an external clock device using FPGAs for every node of the
cluster is currently being developed.
As an additional method for time stamping in a
distributed system, we have implemented an offline
synchronization mechanism in which the unsynchronized local
clocks of the cluster nodes are used to time stamp both
events relevant for our analyses and the arrival of PPS
pulses. Since the precise frequency and offset from UTC
is known for the PPS pulses, the time stamps for the
events can be related to UTC after the measurement in
an offline synchronization process.
We use both httperf and SURGE as load generators for
our web server. SURGE generates traffic patterns similar
to real user behaviour with heavy-tailed distributions
and self-similar traffic as observed empirically in recent
studies of the internet.
We built a simulation model of the Web cluster which includes
relevant aspects of the hardware, operating and communication
systems as well as the application layer as it
is required for a realistic performance evaluation of such
systems. We formulated the model in UML taking into account
both architectural and behavioral aspects and applied
detailed system-level measurements at low loads for determining
the basic parameters. These are mainly one-way
delays which implicitly include other system behavior like
interrupt latencies and show random behavior. We applied
advanced input modeling techniques including multi-modal
distributions, multiple phases, and Bézier curves for unconventional
shapes to adequately represent all quantities.
We also proposed a new model based on differences between successive delays for the autocorrelations observed in the measurements.
The UML simulation model explicitly represents
higher level dynamics which significantly affect the behavior at higher loads including buffering, resource contention, and transport control. The model predicts well the quantiles of the overall delay for HTTP responses.
Prof. Dr.-Ing. Reinhard German
Dr.-Ing. Kai-Steffen Jens Hielscher
web cluster; measurement infrastructure; performance evaluation; distributed web server; GPS; bookshop; UML model; simulation; time synchronization; one-way delays; autocorellation, input modeling
Laufzeit: 1.10.2001 - 6.5.2008
Telefon +49 9131 85 27916, Fax +49 9131 85 27409, E-Mail: email@example.com
|Dietrich, Isabel ; Hielscher, Kai-Steffen Jens ; German, Reinhard: A Measurement-Based Simulation Model of a Web Cluster. In: Krüger, Jörg ; Lisounkin, Alexei ; Schreck, Gerhard (Hrsg.) : 3rd Int. Industrial Simulation Conference (ISC'2005 Berlin, Germany June 9-11, 2005). Ghent, Belgium : EUROSIS-ETI, 2005, S. 88-92. - ISBN 90-77381-18-X|
|Truchat, Sébastien ; Hielscher, Kai-Steffen Jens ; Pflaum, Alexander: Towards Cost Efficient Mobile Services. In: Kotsis, G. ; Taniar, D. ; Ibrahim, I. K. (Hrsg.) : 2nd Int. Conf. on Advances in Mobile Multimedia (MOMM 2004 Bali, Indonesia Sept. 22-24, 2004). Bali : Österreichische Computer Gesellschaft, 2004, S. 179-188. (firstname.lastname@example.org Bd. 184) - ISBN 3-85403-184-X|
|Hielscher, Kai-Steffen Jens ; German, Reinhard: A Low-Cost Infrastructure for High Precision High Volume Performance Measurements of Web Clusters. In: Peter Kemper ; William H. Sanders (Hrsg.) : Proc. 13th Conf. on Computer Performance Evaluations, Modelling Techniques and Tools (TOOLS 2003 Urbana, IL, USA September 2-5,2003). Heidelberg : Springer, 2003, S. 11-28. (Lecture Notes in Computer Science Bd. 2794) - ISBN 3-540-40814-2|
|Hielscher, Kai-Steffen Jens: Aufbau eines clusterbasierten Webservers zur Leistungsanalyse. Erlangen, Friedrich-Alexander-Universität Erlangen-Nürnberg, Dipl-Arb., 2001. - 96 Seiten. |