Quote from: halfawake on August 18, 2014, 04:12:51 AM

I suspect someone started downloading the full blockchain off my full node. Unfortunately, the effect was that my computer came to a screeching halt: moving the mouse and the pressing keys on my keyboard had absolutely no effect for several minutes. When I regained use of my computer, I looked in the Task Manager and bitcoin-qt was using the most RAM, and a fair amount of processing power was being used as well. I turned off bitcoin-qt and the problem went away; anecdotally, I'd say that's reason to believe that running the bitcoin-qt client was causing the problem.

So a little bit about my specs, both internet and computer: I'm using an internet connection of 25 Mbps down / 1.5 Mbps up - reasonable download speed (unfortunately I don't live in an area where gigabit internet is available), but not much on the upload front. My computer has 5 GB of RAM, 250 GB of hard drive space, and a 3 Ghz processor speed. The only part of my computer itself that I feel is underpowered is the RAM, I plan on eventually upgrading to 20 GB RAM, but haven't gotten around to it yet.

So here's my question: is there something about the way the bitcoin client is built that causes my computer to freeze up when people start to download the blockchain from me? Or is this just a case of me not having enough upload bandwidth to handle someone downloading a full node from me? I'd love to be able to support the network by running the bitcoin-qt client regularly, but this is starting to happen semi-regularly as bitcoin becomes more popular and I don't feel like my computer is THAT underpowered.

As you noticed yourself about your specs, I would say the problem is the 5 GB of RAM. You don't mention which OS you are using: a 32 bit version of the OS would typically limit user-space RAM to about 3 GB - that's a bit short for modern apps, especially while running a full node.

What you described (in bold in my quote) is probably caused by what I call "swapping to death". It's the symptom of the OS running out of memory, and because of this, it is forced to swap memory contents back and forth from/to the hard drive, which is about 3 orders of magnitude slower than RAM. This may cause your machine to become completely unresponsive for several minutes.

I always wondered why OS designers wouldn't implement a system warning message whenever the system needs to use the swap file to such an extent that the user experience becomes heavily degraded. Most users don't understand what's happening in the background, and what they can do about it (i.e. add more RAM)