Early numbers on multi-parent diffs

[Aaron Bentley]

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Aaron Bentley wrote:
> I've written an implementation of multi-parent diffs, and early numbers
> do show significant space wins.

More news: they're also fast on read.  I implemented a non-naive text
regeneration routine, and it can regenerate a revision of NEWS 1000
times in  1.81 seconds.  This compares with KnitVersionedFile, which
takes 20.69 seconds, with caching enabled.  (i.e. 11x slower).

(The particular revision is
john at arbash-meinel.com-20070411012920-wnp7rnqdwe13xmhx)

It is still not a fair comparison, because the new code doesn't (can't!)
deserialize any diffs as part of the process.  But with knit caching on,
the knit shouldn't be hitting disk either.

Still, I think these numbers show that MultiParent diffing is
unlikely to slow us down, and that this implementation is quite likely
to speed us up.

As before, the code is at
http://code.aaronbentley.com/bzr/mpknit/

Aaron
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