[Mono-dev] Architectural decisions behind mod_mono

Jay Logue jay-MonoDev at toaster.com
Mon Mar 9 21:12:20 EDT 2009

Tinco Andringa wrote:
>> Unfortunately Microsoft has a long history of confusion on this topic.
>> I remember back when IIS5 was being developed I implored the IIS team
>> make it possible to write filters as kernel modules.  I insisted that
>> the extra kernel transitions needed to invoke my legacy encryption
>> filter was going to kill performance.  Their reaction was 'No way! You
>> might blue-screen the machine!'.  They never did understand that,
>> whether it was in user space or the kernel, if there was a fatal bug in
>> my filter the machine was no more useful than a doorstop.
> Maybe but these kind of performance issues can usually be solved
> through horizontal scaling, something which applications like Facebook
> should have no problem with.
Horizontal scaling is almost always the answer here.  However the 
question is not simply "Can I handle the load?", but rather "At what 
cost per user can I handle the load?".  Thus at a large enough scale the 
efficiency of the request handling infrastructure can become important.

> Bluescreens on shared hosting boxes
> however would be very bad, and the shared hosting market is very
> important for webdevelopment frameworks to attract new developers.
> That and maybe debugging issues, it's tough to debug something if it
> keeps bluescreening on you. If a process dies because of a
> segmentation fault, you just restart the process so it can resume work
> while you figure out what happened. This is significantly less
> downtime, which means especially much for hosting with uptime
> guarantees.
I totally agree with you.  Where the goal is a broad range of 
applications running on as little hardware as possible, fault isolation 
is essential, even if it costs you performance (hence the business of 
VMware).  However sometimes when you're trying to scale a small range of 
tightly controlled applications, the reverse is true, and performance 
becomes more important than isolation.

-- Jay

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