I’ve seen some impressive memory leaks before: a moderately impressive one from Safari in 2010 and a much fancier one from Firefox the following year. But I think they’ve been beaten. In this case, the application in question is NetNewsWire, but I suspect it’s not entirely to blame. I’ve noticed it eating lots of memory a few times before, but this time I managed to put two arbitrarily large numbers together and made another one. What I think is happening is similar to what broke Firefox: a badly behaved script. I’d left some tabs open in NetNewsWire when I left for work, and one of those had some ad banners and possibly even a video on it. And the result of leaving that all day? Well, my iMac wasn’t too unhappy – it responded quickly enough when I unlocked the screen, but displayed a message indicating that it was out of memory and would I like to quit some applications.
Remarkably, Activity Monitor came up without much of a struggle, which allowed me to see what was happening. Sure enough, NetNewsWire was using over 21GB of real memory and a crazy amount of virtual, taking the total to an impressive 70.96GB. I was able to Force Quit it, and then closed a couple of unresponsive applications, at which point the iMac carried on as if nothing had happened. Here’s the evidence, which will get bigger if you click on it: