Re: CGI::Application::Displatch v2, and CGI uploadInfo wierdness

On 1/17/07, John Saylor <jsaylor@xxxxxxxxxxxxxxxx> wrote:
> hi
>
> -----Original Message-----
> From: Dan Horne [mailto:dan.horne@xxxxxxxxxxxxx]
>
> > Well, if you're uploading 20GB of photos then don't you think
> > mod_perl is a bit of overkill?
>
> not so sure i understand what you mean by 'overkill'.
>
> mod_perl will use your web server's resources more efficiently, and with
> 20GB of data to process, i would think these resources would be best
> used on other tasks beside the webserver upload.
>
> the mod_perl API is maybe a bit more difficult than CGI, but not too.
> and it mimics CGI's API in most places.
>
> > From my perspective, you use mod_perl for 2 reasons:
>
> i guess we have different perspectives.
>
> > and mod_perl is a lot more resource intensive than CGI
>
> i find this very difficult to believe. do you have any references/data
> that support this point? everything i've ever read and/or done myself
> has pointed out that mod_perl uses far *fewer* resources than CGI.
mod_perl only improves the startup costs of perl apps.  It doesn't
magically make your perl programs run faster, since it still uses the
same perl interpreter.  But startup costs are usually very high
relative to the total time to process a dynamic page request, so it
can provide a huge speed boost and that is why mod_perl is so great.

But what if your process takes 1 minute, or 5 minutes to run?  How is
that 1 seconds startup savings really going to benefit you?  mod_perl
really doesn't make a different at improving the speed of long running
processes.

As for the cost of running mod_perl...  Most people will preload all
of their application modules at startup to benefit from the memory
sharing.  So your mod_perl processes are generally big.  A CGI script
only loads exactly what it needs, so it is relatively small.  Now that
doesn't really apply in all cases though.  If you only run one app on
the server and the upload script needs all of the applications
modules, then mod_perl will win since mod_perl will share the memory
across many child processes.  But if you have lots of separate
applications on the server (like we have where I work) then one
mod_perl process is absolutely massive wheras the CGI script for a
single app is quite small.

So in that situation a long running script will lock up a very large
and expensive (in terms of memory usage) mod_perl process for a long
time with no noticable speed benefits.

Don't get me wrong, I am a big believer in mod_perl, but it is still
not the right answer 100% of the time (probably just 99% of the time
;) ).

Cheers,

Cees

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