On Thu, Sep 27, 2012 at 02:28:55AM -0400, Jeff King wrote:
> Thanks for reminding me to time. I noticed your a31e626 while digging in
> the history, but forgot that I wanted to do a timing test. Sadly, the
> results are very discouraging. Doing a similar test to your 10,000-refs,
> I get:
>
> $ refs=$(seq 1 10000)
>
> $ . git-completion.bash.old
> $ time __gitcomp_nl "$refs"
> real 0m0.065s
> user 0m0.064s
> sys 0m0.004s
>
> $ . git-completion.bash.new
> $ time __gitcomp_nl "$refs"
> real 0m1.799s
> user 0m1.828s
> sys 0m0.036s
>
> So, a 2700% slowdown. Yuck.
>
> I also tried running it through sed instead of iterating in bash. I know
> that some people will not like the fork, but curiously enough, it was
> not that much faster. Which makes me wonder if part of the slowdown is
> actually bash unquoting the result in compgen.
Ah. The problem is that most of the load comes from my patch 4/3, which
does a separate iteration. Here are the numbers after just patch 3:
$ time __gitcomp_nl "$refs"
real 0m0.344s
user 0m0.392s
sys 0m0.040s
Slower, but not nearly as painful. Here are the numbers using sed[1]
instead:
$ time __gitcomp_nl "$refs"
real 0m0.100s
user 0m0.084s
sys 0m0.016s
So a little slower, but probably acceptable. We could maybe do the same
trick on the output side (although it is a little trickier there,
because we need it in a bash array). Of course, this is Linux; the fork
for sed is way more expensive on some systems.
Still, I'd be curious to see it with the callers (e.g., __git_refs)
doing their own quoting. I'd worry that it would become a maintenance
headache, but perhaps we don't have that many lists we feed (there are a
lot of calls to gitcomp_nl, but they are mostly feeding __git_refs).
-Peff
[1] For reference, that patch is:
diff --git a/contrib/completion/git-completion.bash
b/contrib/completion/git-completion.bash
index 1fc43f7..5ff3742 100644
--- a/contrib/completion/git-completion.bash
+++ b/contrib/completion/git-completion.bash
@@ -225,16 +225,15 @@ __git_quote()
fi
fi
-# Quotes each element of an IFS-delimited list for shell reuse
+# Quotes each element of a newline-delimited list for shell reuse
__git_quote()
{
- local i
- local delim
- for i in $1; do
- local quoted=${i//\'/\'\\\'\'}
- printf "${delim:+$IFS}'%s'" "$quoted"
- delim=t
- done
+ echo "$1" |
+ sed "
+ s/'/'\\\\''/g
+ s/^/'/
+ s/$/'/
+ "
}
# Generates completion reply with compgen, appending a space to possible
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