Re: [hacky PATCH 0/2] speeding up trivial for-each-ref invocations

[Jeff King <peff@peff.net>]

On Mon, Sep 06, 2021 at 09:30:45PM +0800, ZheNing Hu wrote:

> Jeff King <peff@peff.net> 于2021年9月5日周日 下午8:49写道：
> >
> > On Sun, Sep 05, 2021 at 04:19:53PM +0800, ZheNing Hu wrote:
> >
> > > > In this version there are 2 patches, tested against 'git for-each-ref
> > > > --format="%(objectname) %(refname)"' on a fully packed repo with 500k
> > > > refs:
> > > >
> > >
> > > Regarding this 500k refs, is there any way I can reproduce it?
> >
> > Try this in a clone of linux.git (or any other repo):
> >
> >   git rev-list HEAD |
> >   head -500000 |
> >   perl -lne 'print "create refs/foo/$. $_"' |
> >   git update-ref --stdin
> >
> >   git pack-refs --all --prune
> >
> 
> Sorry, It seems that the above command is difficult to complete on my
> machine (it took more than ten minutes). It may be stuck on git update-ref.
> So I tried to reproduce it in a repo which containing 76K refs:

Mine didn't take nearly that wrong, but it does depend on filesystem and
disk performance. It's going to create 500k lock files in refs/foo. :)

You can cheat a bit like this:

  {
    # grab existing packed refs; don't worry about peel lines or the
    # header comment, we're producing a lowest-common denominator
    # version of the file
    grep '^[0-9a-f]' packed-refs

    # now make our new fake refs
    git rev-list HEAD |
    head -500000 |
    perl -lne 'print "$_ refs/foo/$."'
  } >packed-refs.tmp
  mv packed-refs.tmp packed-refs

  # and now ask Git to repack to get everything sorted, etc
  git pack-refs --all --prune

It sounds like you were able to come up with a smaller version to play
with anyway, but I enjoy coming up with such hacks. :)

-Peff