Re: git-fast-import

From: Shawn O. Pearce <spearce@spearce.org>
Date: Feb 7, 2007, 22:55 UTC
Message-ID: <20070207225532.GA1970@spearce.org>
In-Reply-To: <Pine.LNX.4.63.0702071216330.22628@wbgn013.biozentrum.uni-wuerzburg.de>

Johannes Schindelin <Johannes.Schindelin@gmx.de> wrote:

Show 6 quoted lines

> On Wed, 7 Feb 2007, Karl Hasselström wrote:
> > In other words, general history rewriting, but fast.
> 
> For this, it would be better to use a different approach: fast-import 
> still hashes all the objects, which would not be necessary when rewriting. 
> I guess that is what cogito's tool is doing.

gfi doesn't require that it rehash blob objects.

If the blobs in question are already available in the repository gfi is running against (say, from the old branch history) you can just feed those blob SHA-1s at gfi in its 'M' commands when making commits. Yes gfi will need to recompute the tree hashes from scratch, but those are certainly smaller and faster to create than blobs.

So you probably could make a faster history rewriter by taking the output of say `git log --pretty=raw --raw -z`, filter that and reverse it, and stream it into gfi. It probably would kick Cogito's cg-admin-rewritefilter thing in the teeth, as you are forking just one gfi process rather than a thousand git-commit-tree processes.

And if you are doing more complex pathname translations than just picking out a subtree, it also completely avoids needing to read and write index files via update-index, or tree objects by write-tree.

-- 
Shawn.