I have had that happen to me, several time.
I got three different categories of problem with a load higher than what the machine is designed for:
- Incredible Slowdown
In this case, the system is bugged down because it has to swap memory to disk, quickly, back and forth. This will make the server unresponsive until the issue is resolved. If you do not need the server for a while, it may finally come back to normal. If it runs out of memory, you may enter problem #2 or the kernel finally decides to kill a process (maybe because a
NULL and the programmer did not check that case and you get a SEGV...)
- Total Lockup
This is what I would call the usual result for a load that reaches the critical point of your kernel. A place where the kernel cannot even allocate a buffer of memory for itself. This is rare if you have a large (enough) swap file, but it could be that your processes allocate more and more memory non-stop. (As a developer that happens once in a while in my own code, if I do not catch it soon enough, I will have to force a reboot because I won't be able to stop the process and release the memory... IRIX had something to auto-kill such rogue processes, which I thought was really cool.)
Now I had two cases of auto-reboot. In one case I was using a VPS at some company (a while back) and when you were trying to use too much memory, the VPS system would kill the whole machine! So your computer would forcibly be turned off. I still see similar behavior on other VPSes. However, modern ones are more likely to have their kernel kill a process because it requested too much memory. So that process would be down. The VPS itself would still be running... but be rather useless (no daemons running on it...)
On my hardware, I have had that auto-reboot problem. Usually because of two reasons: overload or accessing a piece of hardware either incorrectly (bogus software) or too quickly (which could be viewed as incorrectly too, I guess...) So I had a computer that would just reboot once in a while if my load got too high for too long. I have no clue why it would happen, but I got a different computer since then and did not experience the problem again.
And I also had other auto-reboot where accessing the video board "incorrectly" would somehow send a "hardware" reset to the motherboard. That also results in an auto-reboot. If anything on your computer does such (maybe because of a "slight" incompatibility with a driver) then it could auto-reboot that way too...