Re: Please document the caching and its user options

[Ihor Radchenko]

CCing emacs-devel as I'd like to upgrade this discussion to Emacs-wide
context.

Eli Zaretskii <eliz@gnu.org> writes:

>> ... I wanted to know what is being cached, why, and in what file/directory.
>> 
> >  ...
>> Would it be possible for Emacs to define a framework for cache/var/data
>> locations? Such framework would not only be useful in the context of
>> this discussion, but also to tackle the issue with packages sprinkling
>> things randomly into .emacs.d or ~/ (see
>> https://github.com/emacscollective/no-littering/)
>
> I think Emacs already provides all the framework for caching that is
> needed.  Caching simply means you write some data to file, and all the
> building blocks of that already exist, for quite some time, actually.
> The only thing that is application dependent is the data to be cached
> and how to serialize that, but that cannot be usefully generalized.

I was referring to some kind of global option that defines cache
directory, data directory, etc. Something akin XDG.

Then, Org can place cache inside that directory rather than trying to
cook up something independently.

Also, caching is not as simple, because caches may contain sensitive
data. (see
https://list.orgmode.org/orgmode/CAM9ALR8fuSu0YWS1SehRw7sYxprJFX-r2juXd_DgvCYVKQc95Q@mail.gmail.com/)
Some users may want to move caches to read-restricted location
or even to location dependent on where the cache is originating from
(separate caches depending on whether default-directory is from
encrypted volume, remote mount, etc)

Finally, we got several requests to have caches cleared up upon exiting
Emacs, which is also something that should be better managed centrally,
by Emacs, for all possible kinds of cache/history data.

>> > multisession is an optional package, it is neither preloaded nor
>> > turned on by default in Emacs.
>> 
>> It is used by default in emoji.el (C-x 8 e r)
>
> Which is also optional.  And a minor feature at that.

It is just for now.
TRAMP (by no means a minor feature), has the following TODO item in
tramp-cache.el:

;;; TODO:
;;
;; * Use multisession.el, starting with Emacs 29.1.

>> (Also, should we open some kind of bug report to track documenting
>> multisession in the manual?)
>
> I don't mind, but it sounds like an exaggeration to me.

I kind of agree, if we talk about the current state of affairs. But, I'd
like to discuss this in the context I elaborated on above - more
centralized cache management.

-- 
Ihor Radchenko // yantar92,
Org mode contributor,
Learn more about Org mode at <https://orgmode.org/>.
Support Org development at <https://liberapay.com/org-mode>,
or support my work at <https://liberapay.com/yantar92>