Re: restriction of pulls

[Rogan Dawes <lists@dawes.za.net>]

Johannes Schindelin wrote:
> Hi,
> 
> On Fri, 9 Feb 2007, Christoph Duelli wrote:
> 
>> Is it possible to restrict a chechout, clone or a later pull to some 
>> subdirectory of a repository?
> 
> No. In git, a revision really is a revision, and not a group of file 
> revisions.
> 
> Ciao,
> Dscho
> 

I thought about how this might be implemented, although I'm not entirely 
sure how efficient this will be.

One obstacle to implementing partial checkouts is that one does not know 
which objects have changed or been deleted. One way of addressing this 
is to keep a record of the hashes of all the objects that were NOT 
checked out. (If one does not check out part of a directory, simply 
store the hash of the top level, and you do not need to store the child 
hashes.) This record would be a kind of "negative index".

When deciding what to check in, or which files are modified, one would 
check the "negative index" first to see if an entry exists. If not, only 
then would you check the filesystem to see if modification times have 
changed. With the "negative index", and the files in the file system, 
one would be able to construct new commits, without any problem.

It would also require an updated transfer protocol, which would allow 
the client to specify a tag/commit, then walk the tree that it points to 
to find the portion that the client is looking for, then pull only those 
objects (and possibly their history). This is likely to be VERY 
inefficient in terms of round trips, at least initially.

This might be able to benefit from the shallow checkout support that was 
recently implemented.

Comments?

Rogan