Re: Smart fetch via HTTP?

From: Nicolas Pitre <nico@cam.org>
Date: May 17, 2007, 14:50 UTC
Message-ID: <alpine.LFD.0.99.0705171043070.24220@xanadu.home>
In-Reply-To: <Pine.LNX.4.64.0705171445100.6410@racer.site>

On Thu, 17 May 2007, Johannes Schindelin wrote:

Show 26 quoted lines

> Hi,
> 
> [I missed this mail, because Matthieu culled the Cc list again]
> 
> On Fri, 18 May 2007, Martin Langhoff wrote:
> 
> > On 5/17/07, Matthieu Moy <Matthieu.Moy@imag.fr> wrote:
> >
> > > FYI, bzr uses HTTP range requests, and the introduction of this
> > > feature lead to significant performance improvement for them (bzr is
> > > more dumb-protocol oriented than git is, so that's really important
> > > there). They have this "index file+data file" system too, so you
> > > download the full index file, and then send an HTTP range request to
> > > get only the relevant parts of the data file.
> > 
> > That's the kind of thing I was imagining. Between the index and an
> > additional "index-supplement-for-dumb-protocols" maintained by
> > update-server-info, http ranges can be bent to our evil purposes.
> > 
> > Of course it won't be as network-efficient as the git proto, or even
> > as the git-over-cgi proto, but it'll surely be server-cpu-and-memory
> > efficient. And people will benefit from it without having to do any
> > additional setup.
> 
> Of course, the problem is that only the server can know beforehand which 
> objects are needed.

But the whole idea is that we don't care.

Show 12 quoted lines

> Imagine this:
> 
> X - Y - Z
>   \
>     A
> 
> 
> Client has "X", wants "Z", but not "A". Client needs "Y" and "Z". But 
> client cannot know that it needs "Y" before getting "Z", except if the 
> server says so.
> 
> If you have a solution for that problem, please enlighten me: I don't.

We're talking about a _dumb_ protocol here. If you want something fancy, just use the Git daemon.

Otherwise, you'll simply get everything the remote has that you don't have, including A.

In practice this shouldn't be a problem because people tend to have clean repositories on machines they want their stuff to be published, meaning that those public repos are usually the result of pushes, hence they contain only the minimum set of needed objects. Of course you get every branches and not only a particular one, but that's the price to pay with a dumb protocol.

Nicolas