Re: [PATCH 4/4] fast-import: only store commit objects

From: Michael Haggerty <mhagger@alum.mit.edu>
Date: May 6, 2013, 10:28 UTC
Message-ID: <518785B3.3050606@alum.mit.edu>
In-Reply-To: <CAMP44s1R9hAMZ=DQoPiTVi3+40NpADjVFU7tYovZA8W-PWEhhg@mail.gmail.com>

On 05/03/2013 08:23 PM, Felipe Contreras wrote:

Show 13 quoted lines

> On Fri, May 3, 2013 at 12:56 PM, Thomas Rast <trast@inf.ethz.ch> wrote:
>> Felipe Contreras <felipe.contreras@gmail.com> writes:
> 
>> How do we know that this doesn't break any users of fast-import?  Your
>> comment isn't very reassuring:
>>
>>> the vast majority of them will never be used again
>>
>> So what's with the minority?
> 
> Actually I don't think there's any minority. If the client program
> doesn't store blobs, the blob marks are not used anyway. So there's no
> change.

I haven't been following this conversation in detail, but your proposed change sounds like something that would break cvs2git [1]. Let me explain what cvs2git does and why:

CVS stores all of the revisions of a single file in a single filename,v file in rcsfile(5) format. The revisions are stored as deltas ordered so that a single revision can be reconstructed from a single serial read of the file.

cvs2git reads each of these files once, reconstructing *all* of the revisions for a file in a single go. It then pours them into a git-fast-import stream as blobs and sets a mark on each blob.

Only much later in the conversion does it have enough information to reconstruct tree-wide commits. At that time it outputs git-fast-import data (to a second file) defining the git commits and their ancestry. The contents are defined by referring to the marks of blobs from the first git-fast-import stream file.

This strategy speeds up the conversion *enormously*.

So if I understand correctly that you are proposing to stop allowing marks on blob objects to be set and/or referred to later, then I object vociferously.

If I've misunderstood then I'll go back into my hole :-)

Michael

[1] http://cvs2svn.tigris.org/cvs2git.html

-- 
Michael Haggerty
mhagger@alum.mit.edu
http://softwareswirl.blogspot.com/