Re: How hard would it be to implement sparse fetching/pulling?

Hi,

Jeff Hostetler wrote:

On 11/30/2017 3:03 PM, Jonathan Nieder wrote:

quoted

One piece of missing functionality that looks intereseting to me: that
series batches fetches of the missing blobs involved in a "git
checkout" command:

  https://public-inbox.org/git/20171121211528.21891-14-git@jeffhostetler.com/

But if doesn't batch fetches of the missing blobs involved in a "git
diff <commit> <commit>" command.  That might be a good place to get
your hands dirty. :)

Jonathan Tan added code in unpack-trees to bulk fetch missing blobs
before a checkout.  This is limited to the missing blobs needed for
the target commit.  We need this to make checkout seamless, but it
does mean that checkout may need online access.

Just to clarify: other parts of the series already fetch all missing
blobs that are required for a command.  What that bulk-fetch patch
does is to make that more efficient, by using a single fetch request
to grab all the blobs that are needed for checkout, instead of one
fetch per blob.

This doesn't change the online access requirement: online access is
needed if and only if you don't have the required objects already
available locally.  For example, if at clone time you specified a
sparse checkout pattern and you haven't changed that sparse checkout
pattern, then online access is not needed for checkout.

I've also talked about a pre-fetch capability to bulk fetch missing
blobs in advance of some operation.  You could speed up the above
diff command or back-fill all the blobs I might need before going
offline for a while.

In particular, something like this seems like a very valuable thing to
have when changing the sparse checkout pattern.

Thanks,
Jonathan