Re: fast-import deltas

From: Jonathan Nieder <jrnieder@gmail.com>
Date: Apr 1, 2014, 17:38 UTC
Message-ID: <20140401173856.GC6851@google.com>
In-Reply-To: <xmqqk3b90y79.fsf@gitster.dls.corp.google.com>

Junio C Hamano wrote:

> Assuming that you do have and are willing to read the original file,
> you have three possible (and one impractical) approaches:

[...]

>  - Apply the foreign changes to the original file yourself, and feed
>    the resulting content to fast-import in full, letting fast-import
>    convert into the format Git understands.

This (when importing from Subversion) was the motivation for introducing fast-import's cat-blob command, for what it's worth.

[...]

> In short, the most practical solution would be to reconstitute a
> full object and feed that to fast-import, unless you already have
> xdelta or you can turn your foreign change into xdelta without ever
> looking at the original.

If your delta format happens to be similar enough to xdelta, then streaming in deltas in xdelta format does sound like a neat trick.

Maybe it would be useful to provide a micro-library that creates and validates xdelta opcodes for fast-import frontends to use.

Jonathan