Re: Remote display-time-mail-file

[Eli Zaretskii <eliz@gnu.org>]

> From: Michael Albinus <michael.albinus@gmx.de>
> Cc: Eli Zaretskii <eliz@gnu.org>,  "emacs-devel\@gnu.org" <emacs-devel@gnu.org>
> Date: Fri, 17 Sep 2010 22:59:36 +0200
> 
> Michael Albinus <michael.albinus@gmx.de> writes:
> 
> > Stefan Monnier <monnier@IRO.UMontreal.CA> writes:
> >
> >>> I wouldn't recommend to disable Tramp's file attributes cache at
> >>> all. There are serious performance improvements, using the cache.
> >>
> >> Isn't there some timeout on the cache entries?
> >
> > Some internal ones, like `tramp-completion-reread-directory-timeout'. I
> > could extend it for a general case. I'll check it next days.
> 
> Maybe it's worth to mention, that `tramp-cache-inhibit-cache' does
> something like this:
> 
>   tramp-cache-inhibit-cache is a variable defined in `tramp-cache.el'.
>   Its value is nil
> 
>   Inhibit cache read access, when `t'.
>   `nil' means to accept cache entries unconditionally.  If the
>   value is a timestamp (as returned by `current-time'), cache
>   entries are not used when they have been written before this
>   time.
> 
> If we use a relative time (number of seconds the cache is valid), and
> generalize this variable outside Tramp, it could serve our purposes.

Maybe I'm missing something, but I don't see how this can help.  For
starters, time.el needs Tramp to check the remote every time, so the
cache just gets in the way.

For other use-cases, I wonder how can the cache validity be limited in
terms of time.  Files are modified by programs that access them, not
because some amount of time has passed.  How will a Lisp program that
accesses remote files know which number of seconds to set in this
variable?  What am I missing?