Re: gc --aggressive

From: Jeff King <peff@peff.net>
Date: Apr 17, 2012, 21:58 UTC
Message-ID: <20120417215801.GA10797@sigill.intra.peff.net>
In-Reply-To: <vpqbomqqdxo.fsf@bauges.imag.fr>

On Tue, Apr 17, 2012 at 10:52:03PM +0200, Matthieu Moy wrote:

Show 11 quoted lines

> Jay Soffian <jaysoffian@gmail.com> writes:
> 
> > + 3. `git gc --aggressive`; this is often much slower than (2) because git
> > +    throws out all of the existing deltas and recomputes them from
> > +    scratch. It uses a higher window parameter meaning it will spend
> > +    more time computing, and it may end up with a smaller pack. However,
> > +    unless the repository is known to have initially been poorly packed,
> > +    this option is not needed and will just cause git to perform
> > +    extra work.
> 
> I like your patch.

Me too. I guess it is not surprising since I wrote the initial draft. ;)

> Maybe you should elaborate on "unless the repository is known to have
> initially been poorly packed". My understanding is that --aggressive was
> implemented to be called after an import from another VCS that would
> have computed very poor deltas, but I'm not sure about the details.

Yes, that's exactly it. fast-import will generate packs, but they are often not optimal. So if you have done a big import, you should definitely "git gc --aggressive" as the final step. I don't know how something like a remote-helper would work, where it is fast-importing little bits at a time. Probably a regular repack would be fine, since it will be considering deltas between objects in different packs anyway.

-Peff