Idea about the history horizon

John Arbash Meinel john at
Wed Mar 7 00:01:06 GMT 2007

Nicholas Allen wrote:
> Hi,
> I just had an idea about the history horizon feature. It might not be a
> very good/possible one but thought I would air it anyway ;-)
> I was wondering if it would be possible to have a mode where old
> revisions could be retrieved in the background while you work (and
> commit new revisions). So the horizon is always moving back (perhaps to
> a maximum point in time or maybe eventually to the very first revision).
> The advantage is that it lets you start working on the branch
> immediately if you don't care about all the history at that time.
> Eventually you get a complete mirror but you don't have to wait for a
> complete mirror in order to start being productive. Bzr is silently
> retrieving revisions in the background.
> What do you think?
> Nick

This amounts to having a bzr "service" running in the background. I
think it has some merits, but it potentially adds quite a bit of complexity.

For instance, with the current formats, you need to have a write-lock on
the data when you are adding more information. But since you want this
to be unobtrusive, you probably want to be able to 'commit', and have
the background process get out of the way. (Give up the lock, let you
commit, re-obtain the lock).

Also, I'm don't think filling backwards will play well with our current
formats. I think it is possible to do, but I think the final disk
storage will be rather unoptimal. (.kndx files will need to have 2
records for most items. 1 for the first time you see it, and 1 after
parents have been filled in.)

I know we have discussed other disk formats. Last fall while I was in
Sydney, Robert, Martin and I discussed a possible format that would be
lock-free. It would probably work a lot better for some sort of
"history-filling" operation.

It might also work better with a GUI application, since those tend to be
longer running than command line apps.


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