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List:       apache-modperl
Subject:    Re: squid performance
From:       Leslie Mikesell <les () mcs ! net>
Date:       2000-01-30 20:50:06
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According to Greg Stark:
> Leslie Mikesell <les@mcs.net> writes:
> 
> > The 'something happens' is the part I don't understand.  On a unix
> > server, nothing one httpd process does should affect another
> > one's ability to serve up a static file quickly, mod_perl or
> > not.  (Well, almost anyway). 
> 
> Welcome to the real world however where "something" can and does happen.
> Developers accidentally put untuned SQL code in a new page that takes too long
> to run. Database backups slow down normal processing. Disks crash slowing down
> the RAID array (if you're lucky). Developers include dependencies on services
> like mail directly in the web server instead of handling mail asynchronously
> and mail servers slow down for no reason at all. etc.

Of course.  I have single httpd processes screw up all the time.  They
don't affect the speed of other httpd processes unless they consume
all of the machine's resources or lock something in common.  I suppose
if you have a small limit on the number of backend programs you
could get to a point where they are all busy doing something wrong. 

> > If you are using squid or a caching proxy, those static requests
> > would not be passed to the backend most of the time anyway. 
> 
> Please reread the analysis more carefully. I explained that. That is
> precisely the scenario I'm describing faults in.

I read it, but just wasn't convinced.  I'd like to understand this
better, though.  What did you do to show that there is a difference
when netscape accesses different hostnames for fast static content
as opposed to the same one where a cache responds quickly but
dynamic content is slow?  I thought Netscape would open 6 or so
separate connections regardless and would only wait if all 6
were used.  That is, it should not make anything wait unless you
have dynamically-generated images (or redirects) tying up the
other connections besides the one supplying the main html.  Do
you have some reason to think it will open fewer connections 
if they are all to the same host? 

  Les Mikesell
   les@mcs.com

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