Confused about registry and pruned entries

[Teemu Likonen]

I'm confused with Gnus registry size. There are (at least) two variables
which control registry's size:

 1. gnus-registry-max-entries
 2. gnus-registry-max-pruned-entries

The variable 1 _seems_ clear. No more than that number of entries will
be in the registry. The variable 2 is unclear and the documentation
makes it worse. In the info manual it says:

 -- Variable: gnus-registry-max-pruned-entries
     The maximum number (an integer or `nil' for unlimited) of entries
     the registry will keep after pruning.

So Gnus does some kind of pruning to reduce the registry size. Pruned
entries are gone but variable 2 tells how many to keep.

Let's look at the variable's own documentation (C-h v
gnus-registry-max-pruned-entries):

    Documentation:
    Maximum number of pruned entries in the registry, nil for unlimited.

What? Now it is telling that, even if Gnus prunes something, it keeps
some of those pruned entries in the registry. Variable 2 is telling how
many.

To add the the confusion I checked the registry file. There in the
registry-db expression is keyword :max-hard and :max-soft. It seems that
the variable 1 controls :max-hard and variable 2 :max-soft. This hard
and soft terminology only confuses me more because I understand them
differently than those previous two documentation strings.

So, how do I actually control Gnus registry's size? Let's say I want it
to have maximum of 5000 entries and never grow significantly larger than
that.

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