backward diffs in knits?

[Aaron Bentley]

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Robert Collins wrote:

> That is, rather than patching forward, have a knit be able to patch
> backwards to get content. This works by having the largest text the
> first, and subsequent ones generally remove content rather than adding -
> making the deltas smaller and also happily reducing the read time for
> the most recent text. git packfiles do this with great effect AIUI.

Why would this make deltas smaller?

If you have

Text A
123

and Text B
123456

Then storing A and B requires storing "123" and "456" exactly once, in
either case.  If using forward deltas, "456" is an insert associated
with B, and "123" is part of the A snapshot.  If using backward deltas,
"123" and "456" are both part of the B snapshot.

Aaron
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