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

[Konstantin Ryabitsev <konstantin@linuxfoundation.org>]

On Thu, May 14, 2020 at 07:34:08AM -0700, Caleb Gray wrote:
> I've done some searching around the Internet, mailing lists, and
> reached out in IRC a couple of days ago... and haven't found anyone
> else asking about a long-brewed contribution idea that I'd finally
> like to implement. First I wanted to run it by you guys, though, since
> this is my first time reaching out.
> 
> Assuming my idea doesn't contradict other best practices or standards
> already in place,  I'd like to transform the typical `git clone` flow
> from:
> 
>  Cloning into 'linux'...
>  remote: Enumerating objects: 4154, done.
>  remote: Counting objects: 100% (4154/4154), done.
>  remote: Compressing objects: 100% (2535/2535), done.
>  remote: Total 7344127 (delta 2564), reused 2167 (delta 1612),
> pack-reused 7339973
>  Receiving objects: 100% (7344127/7344127), 1.22 GiB | 8.51 MiB/s, done.
>  Resolving deltas: 100% (6180880/6180880), done.
> 
> To subsequent clones (until cache invalidated) using the "flattened
> cache" version (presumably built while fulfilling the first clone
> request above):
> 
>  Cloning into 'linux'...
>  Receiving cache: 100% (7344127/7344127), 1.22 GiB | 8.51 MiB/s, done.

I don't think it's a common workflow for someone to repeatedly clone 
linux.git. Automated processes like CI would be doing it, but they tend 
to blow away the local disk between jobs, so they are unlikely to 
benefit from any native git local cache for something like this (in 
fact, we recommend that people use clone.bundle files for their CI 
needs, as described here: 
https://www.kernel.org/best-way-to-do-linux-clones-for-your-ci.html).

I believe there's quite a bit of work being done by Gitlab folks to make 
it possible to offload more object fetching to lookaside-caches like 
CDN. Perhaps one of them can provide an update on how that is going.

-K