Re: policy question

[Tom <tom@lemuria.org>]

On Thu, Apr 18, 2002 at 11:47:02PM +0200, Russell Coker wrote:
> > The point is that the reuse of children makes the "fork and change UID"
> > approach impractical. It works for SSH, but not for apache.
> 
> Sure it'll work for Apache!
> 
> On an active web server you don't have equal access to all domains, and each 
> domain will have it's own load spikes.  So if you have co-processes staying 
> around for 30 seconds after being used then you won't have too many running 
> at once.

Sorry, but this is very much impractical in any real-life situation. 
First of all, it would require that apache keep track of which process has 
dropped to what UID and hands off incoming requests according to that table, 
which needs to get updated at each fork and each SIGCHLD.
Two, it also requires that apache handles load independently for each
UID, instead of globally for the whole server, including spare servers
to start or kill, request-handling and forking of new processes. In
short, a total rewrite of a critical component.
Three, on any mass-hosting server, it will drive memory requirements
through the roof within minutes. My company has webservers with
thousands of users. If just 10% of them get accessed at any given time, 
something a few search engine crawls can easily accomplish, we'll have 
several hundred apache instances hanging around, and that is without 
taking into account spare servers.
Four, you would have to fork() much more often than right now. The sole
reason for apache's spare server concept is that forking is so
expensive, so apache tries to avoid it at all costs. Anything that
introduces a considerable increase in forks can not be a good thing.


Which is why I'm trying to do what I need to do without any forks and
without digging deep into apache's heart. Our discussion gave me an
idea or two that I'll be testing. Thanks for the input.


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