Re: VCS_info seems really slow on remote filesystem

[Daniel Shahaf <d.s@daniel.shahaf.name>]

Bart Schaefer wrote on Thu, Nov 07, 2019 at 19:41:13 -0800:
> After some fiddling around to enable function tracing I discovered
> that VCS_INFO_detect_git is trying two different "git rev-parse" calls
> and also looking for two subdirectories, and that
> VCS_INFO_git_getbranch is looking for five more directories and four
> files.  Those directory/file existence tsts are all slow operations on
> this filesystem, and in at least some of the cases appear to be tests
> that would only need to be done if the current directory changed?

The tests are also needed if a git command has been run from another shell.
For example, if you run «git checkout master» in one shell and then press
<Enter> on an empty command line in another shell, that other shell will
re-run vcs_info.

Is the check-for-changes style set?

> Is there anyone more familiar than I with the implementation than I,
> who could determine whether any of this information could be cached
> instead of being regenerated on every precmd?
> 

Possibly.  Question (to the list): Can we invalidate the cache automatically?
For example, could we avoid running all those file/directory existence tests in
VCS_INFO_git_getbranch unless the mtime of .git/<something> has changed since
the last call?  This way, we'd do fewer checks in all cases, not just in slow
mountpoints.

> (I've seen gitstatus recommended in another thread, but it's not
> feasible to install the binary daemon in the circumstances where I'm
> encountering this.)

As a last resort, you can set the disable-patterns style, but it disables
vcs_info completely for the directories it matches; even running vcs_info
interactively at the prompt won't bypass it.  (Arugably it should, though…)