One more word: there was a warning section in result that it has been truncated. I don't really believe this is connected to the problem, but also can't exclude it at the moment.
If so, is there a way to iterate (gently) past $wgAPIMaxResultSize
Okay. Found the answer:
Set revCount=50 and it takes 25 minutes before returning any results.
When it does return, it returns them all at once, which means it held them somewhere (memory presumably) while accumulating them. This should probably be refactored into a generator that does not fetch more from the API until it has yielded all (or most) of what it has already.
Is this the result of throttling perhaps? Seems likely. Is there a way to disable throttling for a single call to fullVersionHistory and instead enforce it between calls to fullVersionHistory for different pages?
21753 200416 2012-02-07T17:25:58Z 21754 200435 2012-02-07T17:45:33Z 21755 200344 2012-02-07T18:10:33Z 21756 200344 2012-02-08T22:42:47Z finished!
real 25m48.924s user 1m19.839s sys 1m4.913s