Some Gnus Registry questions

[Tassilo Horn]

Hi all,

lately I was wondering why emacs increased from taking up 1.4% of my
memory to nearly 5% just immediately after starting Gnus.  By using
Stefan Monnier's excellent memory-usage.el package (especially
`memory-usage-find-large-variables') I was quickly able to identify that
`gnus-registry-db' was the culprit.

So now I've set `gnus-registry-max-entries' to 10000 (from nil), which
has shrunken its size about a factor 5.  Thereby, some questions
wrt. the registry came to my mind.

1) What's `gnus-registry-max-pruned-entries' good for?  Of course I've
   read its docs, but still I have no idea.  What is a pruned entry?

2) The default value of `gnus-registry-track-extra' is (subject sender
   recipient).  When looking at the gnus registry eioio file, I can see
   that especially the subject tracking is responsible for a very large
   portion.  Now the question is: do I actually need that?

   I don't use client-side splitting, so I think the only position where
   I use the registry is for referring articles (^) and gathering
   threads (A T), right?  And since I also use

     (setq gnus-summary-thread-gathering-function
           'gnus-gather-threads-by-references)

   I probably don't need the registry tracking subjects, right?
   
   In the same sense, do I actually need sender and recipient tracking?
   For article referring and thread gathering, I think only the
   Message-Id is needed, right?

Bye,
Tassilo