Re: worktrees vs. alternates

[Derrick Stolee <stolee@gmail.com>]

On 5/16/2018 6:33 AM, Ævar Arnfjörð Bjarmason wrote:
[big snip]
>
> And here's where this isn't at all like "worktree", each of those 100
> will have their own "master" branch, and they can all create 100
> different branches called "topic" that can be different.

This is the biggest difference. You cannot have the same ref checked out 
in multiple worktrees, as they both may edit that ref. The alternates 
allow you to share data in a "read only" fashion. If you have one repo 
that is the "base" repo that manages that objects dir, then that is 
probably a good way to reduce the duplication. I'm not familiar with 
what happens when a "child" repo does 'git gc' or 'git repack', will it 
delete the local objects that is sees exist in the alternate?

GVFS uses alternates in this same way: we create a drive-wide "shared 
object cache" that GVFS manages. We put our prefetch packs filled with 
commits and trees in there, and any loose objects that are downloaded 
via the object virtualization are placed as loose objects in the 
alternate. We also store the multi-pack-index and commit-graph in that 
alternate. This means that the only objects in each src dir are those 
created by the developer doing their normal work.

Thanks,
-Stolee