Introduction to history deltas

[Jan Hudec]

On Wed, Dec 07, 2005 at 14:50:31 +0100, Johan Rydberg wrote:
> Johan Rydberg <jrydberg at gnu.org> writes:
> 
> >> If the knits are packed together for each file, the *number* of fetches
> >> actually *is* O(modified files). The knits are spread over the modified
> >> files, so that's one fetch for each of them. And since the chunks are
> >> ordered by date of addition, you usually want everything from some
> >> offset till the end of file from each of them.
> >
> > I agree with you that in the end what you do is "fetch all missing
> > deltas for knit-file K".  But the way you do it is by fetching delta
> > by delta, based on information from the pulled inventory.  So it is a
> > delta-based, and not file-based, pull.   (see fetch.py)
> 
> I've given this a bit more thought and it should be possible to write a
> somewhat optimized fetcher for knits by simply collecting a set of all
> the deltas needed to be fetched, and then try to fetch as large ranges
> as possible.  So instead of doing;
> 
>  1. fetch revision
>  2. fetch inventory
>  3. fetch knit deltas
>  4. goto 1 if not finished
> 
> You do;
> 
>  1. fetch revision
>  2. fetch inventory
>  3. collect knit deltas 
>  4. goto 1 if not finished
>  5. fetch all knit deltas in the fastest manner possible.

Um, right. Yes.

> This could be implemented by letting Knit have a "join" method that
> takes another knit, and a set of versions to pull.
> 
> Maybe another optimizations can be done to speed it up further. 

I believe it should. Because it makes O(modified files * revisions) to just
O(modified files) -- which does make a difference.

> Another issue with knits is that the inventory knit will become rather
> big, esp if it is shared between several branches (using archives).
> Maybe the inventory and revision knits should be put in the branch
> instead of in a shared "control store."

I will, but in fetch you want all of it anyway.

-- 
						 Jan 'Bulb' Hudec <bulb at ucw.cz>
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