Re: Calculating tree nodes

On 9/4/07, David Tweed [off-list ref] wrote:

On 9/4/07, Jon Smirl [off-list ref] wrote:

quoted

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