Re: Poor performance of git describe in big repos

From: Thomas Rast <trast@inf.ethz.ch>
Date: May 31, 2013, 08:46 UTC
Message-ID: <87y5av4jvj.fsf@linux-k42r.v.cablecom.net>
In-Reply-To: <CAJ-05NOdg5TvjzEMrXaPgogU5z5W6kywZhD-82eTUmvE9Hp=Lw@mail.gmail.com>

Alex Bennée <kernel-hacker@bennee.com> writes:

Show 5 quoted lines

> I think you are right. I was brave (well I assumed the tags would come
> back from the upstream repo) and ran:
>
> git for-each-ref | grep "refs/tags" | grep "commit" | cut -d '/' -f 3
> | xargs git tag -d

So that deleted all unannotated tags pointing at commits, and then it was fast. Curious.

Show 5 quoted lines

> However I have some big commits it seems:
>
> 09:37 ajb@sloy/x86_64 [work.git] >(git for-each-ref | grep ' commit' |
> cut -d\  -f1 | xargs -n1 git cat-file commit) | wc -c
> 1147231984

How many unique entries are there in that list, i.e., what does

  git for-each-ref | grep ' commit' | cut -d\  -f1 | sort -u | wc -l

say?  Perhaps you can also find the biggest commit, e.g. like so:

  git for-each-ref | grep ' commit' | cut -d\  -f1 |
  while read sha; do git cat-file commit $sha | wc -c; done |
  sort -n

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

-- 
Thomas Rast
trast@{inf,student}.ethz.ch