From: Jeff King <peff@peff.net>
Date: Fri, 31 May 2013 16:17:10 GMT
Subject: Re: Poor performance of git describe in big repos
Message-ID: <20130531161710.GB1365@sigill.intra.peff.net>
In-Reply-To: <87txlj30n4.fsf@linux-k42r.v.cablecom.net>

On Fri, May 31, 2013 at 12:27:11PM +0200, Thomas Rast wrote:

> Thomas Rast <trast@inf.ethz.ch> writes:
> 
> > 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
> 
> Actually, Peff, doesn't your commit parent/tree pointer caching give us
> this for free?

It does. You can test it from the "jk/metapacks" branch at
git://github.com/peff/git. After building, you'd need to do:

  $ git gc
  $ git metapack --all --commits

in the target repository. You can check that it's working because "git
rev-list --all --count" should be an order of magnitude faster. You may
need to add "save_commit_buffer = 0" in any commands you are checking,
though, as the optimization can only kick in if parse_commit does not
want to save the buffer as a side effect.

I also looked into trying to just read the beginning part of a commit[1],
but it turned out not to be all that much of an improvement.

-Peff

[1] http://article.gmane.org/gmane.comp.version-control.git/212301