Storage internals: UUID

[John Arbash Meinel]

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> 
>> For hg to do something like that, it would have to pull the
>> entire SVN history and do SHA1 sums the whole way through. Am I
>> right?
> 
> Yes.
> 

Note also that both hg and git 'chain' their hashes. So revision X
with parent Y includes 'Y' in its sha sum. So to inspect a revision in
SVN (revno 10000) requires converting all of the history up to 10000,
compute all of their sha sums, until you get to the identifier for 10000.

There are interesting benefits to this, but Bazaar did explicitly make
the choice that we validate the snapshot more than the full ancestry.
(you can't have a revision which is mentioned but not converted if you
have chained hashes.)

> 
>>> 3) Along those lines, it let's you talk about revisions that
>>> you've never seen. So if it gets converted in the future, it
>>> gets auto-grafted into the right location in history.
>> 
>> This is a little over my head. I'm not sure what "auto-grafted"
>> means. Can you explain again what you mean?
> 
> Suppose I convert just the trunk of a project from Subversion, but 
> whatever I do the convert with knows enough to record that a
> certain revision in corporates a merge from a branch revision.
> 
> Later, I change my mind, go back and convert the branch. The
> additional history naturally associates itself with the previous
> trunk conversion.
> 
> 
> Max.
> 

John
=:->

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