Subject: Re: [PATCH 1/2] blame: large-scale performance rewrite

From: David Kastrup <[email-masked]>
Date: Sat, 26 Apr 2014 19:02:32 +0200

Shawn Pearce <[email-masked]> writes:

> Thanks for doing this. Unfortunately I can't read the patch itself as
> I am also trying to improve JGit's blame code for $DAY_JOB, and JGit
> is BSD licensed.

Actually, I'd have suggested asking $EMPLOYER to buy the rights for
looking at the code, but as I wrote previously, I'd seriously doubt that
he'd get his money's worth for use in a _Java_ implementation.

The C code I proposed is good for files with many small changes: I'd
suggest benchmarking your JGit code with some of them.  If the JGit is
still dominated by unpacking, your implementation should be fine.  The
current C version instead thrashes around digging through its own
all-purpose single linear list.

Here are two real-world test cases:

git://git.savannah.gnu.org/emacs.git
git blame [-M / -C] src/xdisp.c

http://repo.or.cz/r/wortliste.git
git blame [-M / -C] wortliste

The latter one is _really_ taking a severe hit from the O(n^2)
algorithms.  If your benchmarks for that one still point mostly to the
unpacking, your jgit blame should be fine regarding the stuff
I reimplemented.

-- 
David Kastrup