packs and knits

Robert Collins robertc at
Thu Aug 9 00:13:48 BST 2007

On Tue, 2007-08-07 at 18:48 -0400, Aaron Bentley wrote:
> Hash: SHA1
> Robert Collins wrote:
> >> (The fulltexts can be derived from the deltas, so
> >> they are *derivable data* that could optionally be stripped.) 
> > 
> > Equally, the deltas are derivable from the fulltexts ;).
> Oh, you're proposing a VCS where all revisions are stored as fulltexts?
>  Pleased to meet you, Mr. Torvalds. :-D

I think what I was getting at is that some things are duals - fulltexts
and deltas, you can switch between them - and some things are
lossy-on-derivation - e.g. the per-file graph does not have enough
information in it to construct the revision level graph.

So where something is a dual I would argue that any representation is
really just a form of encoding in the storage of the repository - which
clean methods asking for what the caller needs allow the repository to
optimise. And things that are lossy on derivation are different somehow,
probably because you cannot as a repository optimise without actually
storing both the source data and the derived form.

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