Re: Poor performance of git describe in big repos

From: Alex Bennée <kernel-hacker@bennee.com>
Date: Jun 3, 2013, 08:02 UTC
Message-ID: <CAJ-05NNgcj_pPer2Tw4HvKkVib7N1ZFo7rZOrR9z8NMV1WHQsQ@mail.gmail.com>
In-Reply-To: <CAJ-05NN8cARpPTnsCfHt3kY6gTnhZ=Vq55EzqxWBV_3ju-oczQ@mail.gmail.com>

On 31 May 2013 10:57, Alex Bennée <kernel-hacker@bennee.com> wrote:

Show 19 quoted lines

> On 31 May 2013 09:46, Thomas Rast <trast@inf.ethz.ch> wrote:
>>
>> So that deleted all unannotated tags pointing at commits, and then it
>> was fast.  Curious.
>>
>> However, if that turns out to be the culprit, it's not fixable
>> currently[1].  Having commits with insanely long messages is just, well,
>> insane.
>>
>>
>> [1]  unless we do a major rework of the loading infrastructure, so that
>> we can teach it to load only the beginning of a commit as long as we are
>> only interested in parents and such
>
> I'll do a bit of scripting to dig into the nature of these
> uber-commits and try and work out how they cam about. I suspect they
> are simply start of branch states in our broken and disparate history.
>
> I'll get back to you once I've dug a little deeper.

So I wrote a little script [1] which I ran to remove all tags that did not exist on any branches:

git-tag-cleaner.py -d no-branch

After a lot of churning:

17:26 ajb@sloy/x86_64 [work.git] >time /usr/bin/git --no-pager describe --long --tags ajb-build-test-5225-2-gdc0b771

real 0m0.799s user 0m0.024s sys 0m0.052s

So at least I can fix up my repo. All the big ones look at least as though they were weird cvs2svn creations that exist to represent the detached state of a strange CVS tag from the converted repository. However it does raise one question.

Why is git attempting to parse a commit not on the DAG for the branch I'm attempting to describe?

Anyway as I have a work around I'm going to do a slightly more conservative clean of the repo with my script and move on.

[1] https://github.com/stsquad/git-tag-cleaner

-- 
Alex, homepage: http://www.bennee.com/~alex/