how to tell gnus not to fetch entire group list from server

[Michael Slass]

How do I get gnus to ignore groups I'm not subscribed to?

More exactly, every time I try to fetch news and mail, gnus seems to
spend a long time doing this:

,----
| Reading active file from news.comcast.giganews.com via nntp...
`----

And I like that to be faster or less frequent.

The "long time" seems to have started about a week ago, so I must have
accidentally changed something.  What can I change so that gnus won't
waste time looking up groups that I don't care about, and the articles
in them?

Thanks. 
-- 
Mike Slass