On Tue, May 08, 2007 at 11:38:46AM -0400, Nicolas Pitre wrote:
> On Tue, 8 May 2007, Theodore Ts'o wrote:
>
> > Signed-off-by: "Theodore Ts'o" <tytso@xxxxxxx>
>
> I'd prefer if tests were performed on the performance impact before
> changing the default depth. If done separately from this patch then the
> commit log could contain those results as well.
The following results are on a recent git repository, using time to
record the real, user, and sys times on the two commands: "git-gc
--no-reuse-delta --window=X --depth=Y" and "git log --pretty=oneline
-S'object' > /dev/null". All of these tests were done with a hot
cache, so disk speed didn't enter into the calculations.
git-gc git log -S'object' pack size
w=10,d=10 27.1s/25.2s/0.3s 20.8s/20.4s/0.1s 15292k
w=10,d=30 23.8s/22.3s/0.2s 21.2s/20.9s/0.1s 12996k
w=10,d=50 24.8s/22.4s/0.4s 21.8s/21.2s/0.1s 12340k
w=100,d=100 24.1s/22.8s/0.3s 22.4s/21.8s/0.2s 11772k
w=30,d=10 45.0s/43.1s/0.4s 20.8s/20.5s/0.1s 14388k
w=30,d=30 35.8s/34.1s/0.3s 21.6s/21.1s/0.1s 11800k
w=30,d=50 34.6s/33.0s/0.3s 22.1s/21.4s/0.1s 11376k
w=30,d=100 34.0s/32.2s/0.3s 22.2s/21.6s/0.1s 11012k
w=50,d=10 56.1s/54.3s/0.4s 21.3s/20.5s/0.1s 14224k
w=50,d=30 47.2s/45.4s/0.4s 21.6s/21.0s/0.1s 11496k
w=50,d=50 44.5s/43.0s/0.3s 21.7s/21.2s/0.1s 11108k
w=50,d=100 44.3s/42.7s/0.4s 22.4s/21.7s/0.1s 10824k
So a couple of things immediately become evident. First of all, as
Junio predicted, changing --depth makes no difference to the git-gc or
git log times. The latter is thanks to the delta chaching. Secondly,
changing --depth does make a signficiant difference to the pack size.
Finally, --window does help somewhat in reducing the pack size, but it
_significantly_ increases the time to calculate the pack.
My conclusion given this quick benchmark is that it seems to me that
changing the defaults of --depth to 50, and keeping --window at 10, is
a reasonable thing to do.
Regards,
- Ted
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