Question about the ahead-behind computation and status

[Jeff Hostetler <git@jeffhostetler.com>]

We working with the (enormous) Windows repo, we observed
a performance problem in the ahead-behind computation and
were considering a few options.

We had a local repo with a local branch that was 150K
commits behind the upstream branch[*].  There was a ~20
second different in the run times for these 2 commands:

     $ git status --porcelain=v2
     $ git status --porcelain=v2 --branch

Profiling showed the additional time was spent computing
the ahead/behind values for the branch.  (The problem is
not specific to porcelain V2, that was just the command
where we discovered it; for example, there is a similar
perf problem in "git branch" vs "git branch -vv".)

I don't want to jump into the graph algorithm at this time,
but was wondering about adding a --no-ahead-behind flag (or
something similar or a config setting) that would disable
the a/b computation during status.

For status V2 output, we could omit the "# branch.ab x y"
line.  For normal status output, change the prose a/b
message to say something like "are [not] up to date".

Thoughts or suggestions ???

Thanks,
Jeff


[*] Sadly, the local repo was only about 20 days out of
     date (including the Thanksgiving holidays)....