However, I verified there are actually no more than less than
3,000 articles.  It should not be a cause of this problem.

> It took ~2 minutes to display its question
> "How many articles...?" and the memory usage was at 555 MB (RSS).
> When I answered "500" and the summary buffer finally appeared, it grew
> up to 893 MB.  Which is a bit scary, since my computer has "only" 1 GB
> of RAM and is now already paging quite a bit.

> Will this become better if I subscribe to the newsgroup and catch up?
> In any case I probably will have to kill my current Emacs session soon.

The real cause is that Gnus first expands this ACTIVE data into:

(3437 3438 3439 3440 ...... 30538696 30538697 30538698 30538699)

If you run Emacs on a super computer, try this: