Re: link is broken

[Shu Yuan Chang <shuyuanc@usc.edu>]

hi there,
   could anyone kindly tell me where to find those files URLed in the
followling
link, the hyperlink is broken?

  thanks!

Shu


Haobo Yu wrote:

> In this email I'll briefly explain a lesson we learned from tuning
> the memory usage of a large-scale (wrt traffic) simulation. Hopefully
> it'll be useful for others. Here ns is referred to the current snapshot.
>
> Originally tcl/ex/large-scale-web-traffic.tcl was a self-similar web
> traffic model used in "Dynamics of {IP} Traffic: A study of the role of
> variability and the impact of control", SIGCOMM'99. It was implemented
> completely in otcl (tcl/http/http-mod.tcl). When there are 400 HTTP
> sessions and with the parameters given in that script, its memory usage
> linearly increases with time, and the simulation ends with about 800+MB
> memory (see http://www.isi.edu/~haoboy/old-usage-400.ps).
>
> There are two factors that contributed to this. First, http-mod.tcl
> allocates various split objects using 'new', but does not _explicitly_
> 'delete' them in otcl. It turns out that this caused a memory leak every
> time that new-ed split object is reassigned a value. Second, implementing
> things, including HTTP pages, objects, completely in otcl takes a lot of
> extra memory than to maintaining those complex data structures in C++.
>
> After redesigning the HTTP traffic model and implementing the data
> structures completely in C++, we cut down memory usage to be stabilized
> around 62MB for a 400 session simulation
> (http://www.isi.edu/~haoboy/new-usage-400.ps).
>
> However, a sad news is, moving things into C++ does not help much in
> reducing executaion time. This is because packet passing in ns is
> completely done in C++, and that's the main cause of the long execution
> time (assuming there's enough memory).
>
> The lesson we learned is: (1) be very careful about 'new' and 'delete'
> about split objects, and (2) always maintain complex data structures in
> C++.
>
> Hope this will be helpful for others.
>
> - Haobo