bug#36714: 27.0.50; Gnus nnmaildir taking long time to recursively visit sub-Maildirs

[Eric Abrahamsen <eric@ericabrahamsen.net>]

Jean Louis <bugs@gnu.support> writes:

> * Eric Abrahamsen <eric@ericabrahamsen.net> [2019-07-22 19:40]:

[...]

>> I also don't think this threatens the integrity of the user's files: the
>> extra data is maintained in parallel, and doesn't interfere with the
>> messages themselves.
>
> I did read nnmaildir info page, and I have not found anything that
> would indicate what would Gnus do to my file system.

The first paragraph of the maildir section of the Gnus manual says:

‘nnmaildir’ also stores extra information in the ‘.nnmaildir/’ directory
within a maildir.

On the next page of the manual, there's a section on this group parameter:

‘nov-cache-size’
     An integer specifying the size of the NOV memory cache.  To speed
     things up, ‘nnmaildir’ keeps NOV data in memory for a limited
     number of articles in each group.  (This is probably not
     worthwhile, and will probably be removed in the future.)  This
     parameter’s value is noticed only the first time a group is seen
     after the server is opened—i.e., when you first start Gnus,
     typically.  The NOV cache is never resized until the server is
     closed and reopened.  The default is an estimate of the number of
     articles that would be displayed in the summary buffer: a count of
     articles that are either marked with ‘tick’ or not marked with
     ‘read’, plus a little extra.

Noting both that the nov cache will probably go away at some point, and
how to control its size in the meantime.

(add-to-list 'gnus-parameters
	     '("^nnmaildir:"
	       (nov-cache-size . 2)
	       (expire-age . never)))