Re: Calculating tree nodes

["Jon Smirl" <jonsmirl@gmail.com>]

On 9/4/07, David Tweed <david.tweed@gmail.com> wrote:
> On 9/4/07, Jon Smirl <jonsmirl@gmail.com> wrote:
> > Git has picked up the hierarchical storage scheme since it was built
> > on a hierarchical file system.
>
> FWIW my memory is that initial git used path-to-blob lists (as you're
> describing but without delta-ing) and tree nodes were added after a
> couple of weeks, the motivation _at the time_ being they were a
> natural way to dramatically reduce the size of repos.
>
> One of the nice things about tree nodes is that for doing a diff
> between versions you can, to overwhelming probability, decide
> equality/inequality of two arbitrarily deep and complicated subtrees
> by comparing 40 characters, regardless of how remote and convoluted
> their common ancestry. With delta chains don't you end up having to
> trace back to a common "entry" in the history? (Of course, I don't
> know how packs affect this - presumably there's some delta chasing to
> get to the bare objects as well.)

While it is a 40 character compare, how many disk accesses were needed
to get those two SHAs into memory?

>
> --
> cheers, dave tweed__________________________
> david.tweed@gmail.com
> Rm 124, School of Systems Engineering, University of Reading.
> "we had no idea that when we added templates we were adding a Turing-
> complete compile-time language." -- C++ standardisation committee
>


-- 
Jon Smirl
jonsmirl@gmail.com