backward diffs in knits?

[Aaron Bentley]

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John Arbash Meinel wrote:
> I think that in the common case of files growing, backwards deltas are
> slightly smaller, and it optimizes for extracting the TIP revision,
> which helps for things like "bzr checkout", "bzr update", and "bzr diff".

Well, diff is already handled by using the basis tree, right?

> When I was discussing this stuff with Martin and Robert, I didn't think
> the idea was to actually store backwards deltas in Knits, but a
> different storage format.

It sounds like they're now considering storing backwards deltas in Knits.

> I don't know how much compression one could get. But at least the Xorg
> folks said that their packed history is approx the same size as a checkout.

Do they do in-tree builds?  That would skew the numbers a lot.

> Speaking of which, we might also consider using .7z as a storage format.

.7z has never struck me as a widely supported supported system, but if
there are high-quality implementations available, I guess that's okay.
Certainly, its other characteristics sound nice.

Aaron
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