Re: Add a "Flattened Cache" to `git --clone`?

From: Junio C Hamano <gitster@pobox.com>
Date: May 14, 2020, 22:30 UTC
Message-ID: <xmqqeermp2sw.fsf@gitster.c.googlers.com>
In-Reply-To: <CAGjfG9akT+KG-tttRWEX_ZqxrqPoY_4Ed7Pymt4DkV5Rgc1CEA@mail.gmail.com>

Caleb Gray <hey@calebgray.com> writes:

> Actually those are the steps that I'm explicitly hoping can be
> skipped, both on server and client, after the first successful clone
> request transaction. The cache itself would be of the end resulting
> `.git` directory (client side)... unless I have misconceptions about

If you look at .git/objects/pack/ directory in your repository that is a clone of somebody else, most likely you'd find even number of files in there, those whose filename ends with .pack and their counterparts whose filename ends with .idx extension. Both files must exist to perform any local operation, but during the initial cloning, only the bits in the former are transferred, and the contents of the latter must be constructed from the bits in the former.

You can introduce a new protocol that copies the contents of the .idx, but the contents of that file MUST be validated on the receiving end, which entails the same amount of computation as our clients currently spend to construct it out of .pack, so in the end, you'd be wasting more bandwidth to transfer .idx which is redundant information without saving processing cycles.