Re: Mercurial 0.3 vs git benchmarks

[Matt Mackall]

On Mon, Apr 25, 2005 at 07:08:28PM -0700, Linus Torvalds wrote:
> 
> 
> On Mon, 25 Apr 2005, Matt Mackall wrote:
> >
> > Here are the results of checking in the first 12 releases of Linux 2.6
> > into empty repositories for Mercurial v0.3 (hg) and git-pasky-0.7.
> > This is on my 512M Pentium M laptop. Times are in seconds.
> > 
> >                  user         system       real        du -sh
> > ver    files   hg    git    hg    git    hg    git    hg   git
> > 
> > 2.6.0  15007 19.949 35.526 3.171 2.264 25.138 87.994 145M   89M
> > 2.6.1    998  5.906  4.018 0.573 0.464 10.267  5.937 146M   99M
> > 2.6.2   2370  9.696 13.051 0.752 0.652 12.970 15.167 150M  117M
> > 2.6.3   1906 10.528 11.509 0.816 0.639 18.406 14.318 152M  135M
> > 2.6.4   3185 11.140  7.380 0.997 0.731 15.265 12.412 156M  158M
> > 2.6.5   2261 10.961  6.939 0.843 0.640 20.564  8.522 158M  177M
> > 2.6.6   2642 11.803 10.043 0.870 0.678 22.360 11.515 162M  197M
> > 2.6.7   3772 18.411 15.243 1.189 0.915 32.397 21.498 165M  227M
> > 2.6.8   4604 20.922 16.054 1.406 1.041 39.622 25.056 172M  262M
> > 2.6.9   4712 19.306 12.145 1.421 1.102 35.663 24.958 179M  297M
> > 2.6.10  5384 23.022 18.154 1.393 1.182 40.947 32.085 186M  338M
> > 2.6.11  5662 27.211 19.138 1.791 1.253 42.605 31.902 193M  379M
> 
> That time in checking things in is worrisome.
> 
> "git" is basically linear in the size of the patch, which is what I want,
> since most patches I work with are a couple of files at most. The patches
> you are checking in are huge - I never actually work with a change that is
> as big as a whole release. I work with changes that are five files or
> something.

Git (and hg) commit time should be basically linear in the number of
files touched, not the size of the patch.

> "hg" seems to basically slow down the more patches you have applied. It's 
> hard to tell from the limited test set, but look at "user" time. It seems 
> to increase from 6 seconds to 27 seconds.

And the number of files checked in grows from ~1000 to ~6000. Note
that git is growing from 4 to 19 seconds as well. Interestingly:

19.138/4.018 = 4.76 (git time ratio)
27.211/5.906 = 4.61 (hg time ratio)

So the scaling here is pretty similar.

> To make an interesting benchmark, try applying the first 200 patches in 
> the current git kernel archive. Can you do them three per second? THAT is 
> the thing you should optimize for, not checking in huge changes.

I'm not versant enough with git enough to know how but I'll give it a
shot. Do you have the patches in an mbox, perchance? This is Andrew's
x/198 patch bomb? It might be simpler for me to just apply everything
in -mm to git and hg and compare times. Modulo python startup time, it
should be pretty similar.

Oh, and can you send me the script you used for your test with git?

> If you're checking in a change to 1000+ files, you're doing something
> wrong.

That's primarily to demonstrate the scalability and show the
divergence in repository sizes.

However, it will not be uncommon for developers to pull/merge changes that
large and the numbers here will be about the same for hg.

> > Full-tree working dir diff (2.6.0 base with 2.6.1 in working dir):
> > hg:  real 4.920s  user 4.629s  sys 0.260s
> > git: real 3.531s  user 1.869s  sys 0.862s
> > (this needed an update-cache --refresh on top of git commit, which
> > took another: real 2m52.764s  user 2.833s  sys 1.008s)
> 
> You're doing something wrong with git here. Why would you need to update 
> your cache?

Quite possibly. Without it, I was getting a dump of a bunch of SHAs.
I'm pretty git-ignorant, I've been focusing on something else for the
past couple weeks.

-- 
Mathematics is the supreme nostalgia of our time.
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