Re: [PATCH 0/3] Un-pessimize "diff-index $commit -- $pathspec"

From: Junio C Hamano <gitster@pobox.com>
Date: Aug 29, 2011, 22:05 UTC
Message-ID: <7v1uw36fgb.fsf@alter.siamese.dyndns.org>
In-Reply-To: <CA+55aFzk+hn9wMAp3H92SHAGO8CQVBpTsmR41FgCy32T7muUzA@mail.gmail.com>

Linus Torvalds <torvalds@linux-foundation.org> writes:

Show 14 quoted lines

> On Mon, Aug 29, 2011 at 2:33 PM, Junio C Hamano <gitster@pobox.com> wrote:
>>
>> Before and after applying this series, looking for changes in the kernel
>> repository with a fairly narrow pathspec gets a moderate speeds up.
>
> "moderate speeds up"?
>
> Looks like a big win to me. Admittedly it's already a pretty fast
> operation, but script it and repeat it a million times, and that will
> matter a lot more.
>
> I guess the "--raw" diff part means that you are hiding the time to
> make a real diff, which would otherwise swamp everything else. Even
> so, this looks like a good improvement.

The topic started by Marat Radchenko in

    http://thread.gmane.org/gmane.comp.version-control.git/179926

who was trying to pick a single path (we do not know how deep it is), and was comparing between these two:

  $ time git show branch:file | diff -u - file > /dev/null 
  real    0m0.003s
  user    0m0.000s
  sys     0m0.000s
  $ time git diff branch -- file > /dev/null 
  real    0m31.442s
  user    0m31.040s
  sys     0m0.380s

Replacing "diff -u" with "git diff --no-index" in the former didn't make much of a difference. It turned out that Marat had 603k paths in the index and the most of the time was spent in the unpack machinery.