on when to checksum

[Tom Lord <lord@emf.net>]

Linus, 

I think you have made a mistake by moving the sha1 checksum from the
zipped form to the inflated form.  Here is why:

What you have set in motion with `git' is an ad-hoc p2p network for
sharing filesystem trees -- a global distributed filesystem.  I
believe your starter here has a good chance of taking off to be much,
much larger than just a tool for the kernel.

A subset of your work: blobs and blob databaes, has much wider application
than just sharing trees:  Those parts of `git' can form a very solid 
foundation for many other applications as well.   To the extent `git'
succeeds in the context of the kernel, it will be invested in and
extended and generalized --- and the kernel project will benefit.
So don't ignore those wider applications even though they are not your
focus today: they will generate investment that feeds back to your project.

Your `git' is silent on transports and mirroring of blob databases --
tasks for scripting, sure -- but those elements won't be far behind.

Eventually, slinging around blobs as atomic elements
of payloads will become very common.

The blob handle (aka "address")/payload model of a blob db is very
clean and simple.   In a network of nodes speaking to one and other
by exchanging blobs, I forsee a prominent need for intermediate
nodes that process blobs "blindly" and as quickly as possible.

Blob compression is mostly goofy if regarded just as a way to 
save on (diminishingly cheap) disk space but it is mostly 
sane if regarded as a way to cut the cost of network bandwidth
roughly in half.

Must intermediate nodes inflate the payloads passing through them
or which they cache just to validate them?   That's not a desirable otucome
for many obvious reasonhs.

There *are* concerns about checksumming zips: it is necessary to nail
down the zip process and make sure it is absolutely and permanently
deterministic for this application.   But *that* is the problem to 
solve, not avoid by moving what the checksum refers to.

Thanks,
-t