Subject: Re: Poor performance of git describe in big repos

From: Thomas Rast <[email-masked]>
Date: Fri, 31 May 2013 10:46:24 +0200

Alex Bennée <[email-masked]> writes:

> 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.

> 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