revision-history considered harmful

[Martin Pool]

On Thu, 2005-12-22 at 22:34 -0600, John A Meinel wrote:
> Robert Collins wrote:

> > The revision-history file is somewhat special - its not reconstructable,
> > which makes it precious, its only identified by a URL, which makes URL's
> > important (where all our other data is not sensitive to things moving
> > around).
> > 
> > Martin and I sketched an approach where commits record the revno they
> > had at the time of commit, which combined with the branch nickname means
> > that doing a 'switch' of the revision-history when you 'pull' would be
> > understandable to users: you would *always* end up with the revno of the
> > branch you pulled from. 

Perhaps I've forgotten but I didn't think this required recording the
revno.  Rather, we'll just say that the revision-history must always be
equal to the left-hand path through the revisions: that is, taking the
primary parent, which comes first in the list.
 
> > We thought we could trial this by simply making the revision-history
> > replacement function of '--overwrite' always be on, without disabling
> > the divergence check. If that satisfied people, we can nuke
> > revision-history-the-file.

> I'm +1 the concept of always writing the complete ancestry. Basically
> getting rid of convergence.

I think of it as making convergence stronger: once you've pulled, you're
not just at the same point, but you have the same apparent path for
getting there.  But you can look at it either way.

> I don't know if we want to actually delete the revision-history file, as
> it seems to be a decent optimization for stuff like "-r 12".
> But yes, I think we could change pull.

I agree, probably useful to keep it just as a cache.  The check command
could make sure it's consistent.

-- 
Martin

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