Next Steps for hpss, etc

[John Arbash Meinel]

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I'm roughly finishing up my current work items, and figured I'd put out
some ideas for what I should be working on next. We've mentioned wanting
to do a bit more collaboration, so at least working in the same area,
even if we aren't working on the same bug.

The top two items in my head are:

1) Commit to stacked branch
2) Shallow branching
   As defined by, creating a stacked local copy that has the data it
   needed to create the working copy, and no further policy. (It
   doesn't explicitly cache, but it doesn't avoid extra history, either)


(1) seems like a prerequisite for (2). Since having a shallow branch
doesn't help you if you still can't commit to it.
(2) seems like something that could use a really good HPSS verb for
"give me everything I need to start hacking on the tip revision of this
branch".

I've considered making it a branch that will cache anything it has to
access (so any time it falls back to the stacked-on repository, it will
save that data locally.) The primary reason I would skip that, is
because inserting into a repository is transactional. We require both a
write lock, and a write group that is then committed. And defining the
transaction boundaries during an otherwise read-only operation is
difficult at best.
Also, you get into problems of data model violation. (log needs to look
at only the revision texts, but the presence of a revision text implies
the presence of the associated inventory and texts.)


I think the two of these would be very good for UDD stuff. Since it
allows people to download ~tarball sized content, and still gives them a
branch they can hack on and upload.

I also think most of the bits are there, so we can migrate
incrementally, rather than having to do a large amount of work to get
anything that can land.

I also think these two things could be worked on in parallel. You may
end up with a shallow branch that you can't commit to yet, but it would
still be a productive thing to get done.

Thoughts?

John
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