Comment 22 for bug 118625

Okay, I think that comment 20 might indeed be the secret here, specifically the slowndown issue. I can produce some pretty extreme slowdowns on my local machine (an AnnotateUI that usually takes 2 seconds takes 60) by making every single request build a revision graph and then hitting loggerhead with 15 simultaneous users.

If I don't force loggerhead to rebuild the revision graph on every request, it stays relatively fast even when being hit with 15 simultaneous users, though the initial "rebuild the revision graph" process takes 15 seconds because it's being done by so many threads at once.

So this may in fact not be a hang, but simply an extreme slowdown by having many threads all attempt to build a revision graph at once for very large branches, and then due to the way Paste works, no new threads are spawned (they would be so slow anyway, who cares) and you get a task backup and a "hang".