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From "Roy T. Fielding" <field...@ebuilt.com>
Subject INRIA paper on Traffic Model and Performance Evaluation of Web Servers
Date Fri, 05 Oct 2001 06:43:16 GMT
I ran across this by accident while searching for something else.
The research is excellent, albeit packed with a bit too much statistics
for a casual reader.

....Roy

http://www.inria.fr/rrrt/rr-3840.html

RR-3840 - Traffic Model and Performance Evaluation of Web Servers 

Liu, Zhen - Niclausse, Nicolas - Jalpa-Villanueva, Cesar - Barbier, Sylvain 
Rapport de recherche de l'INRIA- Sophia Antipolis [in English], Dec. 1999.

  [get the postcript -- the PDF suffers from the latex fonts]

Abstract : In this paper we present a new model of Web traffic and its
applications in the performance evaluation of Web servers. We consider
typical behavior of a user's hypertext navigation within a Web server.
We propose a traffic model at the session level, formulated as a stochastic
marked point process, which describes when users arrive and how they browse
the server. We provide results of statistical analyses and goodness-of-fit
of various simple parametric distributions and of their mixtures.
We developed a Web server benchmark: WAGON (Web trAffic GeneratOr and
beNchmark), and we validated the traffic model by comparing various
characteristics of the synthetic traffic generated by WAGON against
measurements. We then report benchmark and analysis results on the
Apache server, the currently most used Web server software. We analyze
the impact of the traffic parameters on the HTTP request arrival process
and the packet arrival process. We also show that the aggregate traffic is
self-similar in most cases, and that, more importantly, the Hurst parameter
is increasing in the traffic intensity. We further provide performance
comparison results between HTTP1.0 and HTTP1.1 and show that HTTP1.1 could
be much worse for users as well as for servers if some control parameters
of the server and of browsers are incorrectly set.  Indeed, when the server
load is relatively high, the page response time under HTTP1.1 increases
exponentially fast with the number of parallel persistent connections and
with the timeout value used in Apache for persistent connections.
We investigate the impact of user network conditions on the server
performance. We also propose a queueing model to analyze the workload of
persistent connections on the Apache server, and we establish optimal
solution of the timeout parameter for the minimization of workload.

Based on our analyses, we suggest the following practical guidelines.
It is usually beneficial for both Web servers and Web clients to use
HTTP1.1 instead of HTTP1.0. When HTTP1.1 is used, it should be used with
pipeline. In terms of the management of persistent connections, it is
useful for browsers to implement Early Close policy which combines the
advantages of both HTTP1.0 and HTTP1.1.  Browsers should in general,
except for users with low bandwidth network connections (such as Modem),
avoid establishing multiple parallel persistent connections from one
browser window to the same Web server. On the server side, servers should
set small timeout values for persistent connections if fixed timeout
control mechanism is used (as in Apache) or if dynamic timeout control
mechanism is used and the measured workload is high. 


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