admin question: howto-unresponsive server under extreme load

[Nicholas Leippe]

We have a webserver that occasionally gets pegged. When this happens, the 
remote shell becomes nearly totally unresponsive--to the point that we have 
it rebooted at the colo. We already have swap disabled. We are trying to 
pinpoint which bit of our application is causing this. Obviously, a hard 
reset kills any chance of it completing and writing log files with useful 
clues.

Is there some way to lock a root shell such that it is always responsive so 
that we could at least kill the webserver and have a chance of the log files 
being fully written to find the problem?

RT scheduling? Tell bash to mlock() itself into memory? Ideas?