Re: git diff infinite loop at attempt to diff two specific commits

[Matt Pearson <404emailnotfound@gmail.com>]

[ please don't prune the CC list; I've re-added Björn ]

On Sun, Jul 5, 2009 at 16:09, Alexander
Toresson<alexander.toresson@gmail.com> wrote:
> 2009/7/5 Matt Pearson <404emailnotfound@gmail.com>:
>> 2009/7/5 Björn Steinbrink <B.Steinbrink@gmx.de>:
>>> On 2009.07.05 19:37:44 +0200, Alexander Toresson wrote:
>>>> Hello,
>>>>
>>>> I've got problems with git diff, it hangs in an infinite loop when
>>>> attempting to generate a diff between two specific commits. Commands
>>>> to reproduce:
>>>>
>>>> git clone git://eulex.zapto.org/nightfall.git
>>>> cd nightfall
>>>> git diff --stat 597711..61a139
>>>>
>>>> (Note that the clone needs to fetch 16mb)
>>>>
>>>> I'm running git 1.6.3.3.
>>>
>>> FWIW, it "hangs" on the save.xml file. The old version is 1.2M, the new
>>> one is 9M. Using the patience diff algorithm to compare them takes about
>>> 5 seconds here, while the default algorithm took 6m15s.
>>
>> I can confirm this for the 1.6.0.4 shipped with Ubuntu Jaunty (so this
>> would seem to not be a recent change). Actually, it may be worse: mine
>> is still running after 8 minutes, and this machine is almost
>> brand-new. Normal diff -u on the two versions of the file finishes in
>> under a second.
>>
>> On an unrelated note, it's usually a bad idea to have files like
>> configure and *.suo in the repo (and possibly this save.xml as well).
>>
>
> Ah! I shouldn't really have had that file in version control, I can
> understand that it would be slow to diff a 9mb xml file. On the other
> hand, is there a way to mark the file so git won't attempt to diff it,
> but will just dispose of the old contents and use the new contents?
>
> As for the configure file, it's convenient for users to not have to
> have autoconf installed to build it. I don't really know what *.suo
> does nor do I think I added it, so I'll check up on that.
>
> Thank you.

Slow is a relative term; Git is still taking several orders of
magnitude longer than it should even on such a large file (it takes
over 10 times as long as diffing v2.6.11 to HEAD on the kernel tree,
and that patch is ~400 MB). Plus, as I noted above, GNU diff can do it
in less than a second.

You can disable diffing by adding the following line to .gitattributes
(see gitattributes(5)):
save.xml -diff

Having the configure script in the repo pollutes the diffs. Anybody
who's going to check a project out of source control (instead of using
a tarball) will not have a problem running autoreconf once to get
things working. *.suo and *.vcproj.user contain user-specific settings
for the Visual Studio solution and project, and shouldn't be tracked
in git either. You should really create a proper .gitignore for your
project.

Matt