Re: tb/cruft-packs (was Re: What's cooking in git.git (Mar 2022, #01; Thu, 3))

> Derrick Stolee wrote:
>> On 3/7/2022 1:18 PM, Taylor Blau wrote:
>>> On Mon, Mar 07, 2022 at 10:06:00AM -0800, Jonathan Nieder wrote:
> 
>>>>  2. Marking this as a repository format extension so it doesn't interact
>>>>     poorly with Git implementations (including older versions of Git
>>>>     itself) that are not aware of the new feature
>>>
>>> The design of cruft packs was done intentionally to avoid needing a
>>> format extension. The cruft pack is "just a pack" to any older version
>>> of Git. The only thing an older version of Git wouldn't understand is
>>> how to interpret the .mtimes file. But that's no different than the
>>> current behavior without cruft packs, where any unreachable object
>>> inherits the mtime of its containing pack.
>>>
>>> So an older version of Git might prune a different set of objects than a
>>> version that understands cruft packs depending on the contents of the
>>> .mtimes file, the mtime of the cruft pack, and the width of the grace
>>> period. But I think by downgrading you are more or less buying into the
>>> existing behavior. So I don't think there is a compelling reason to
>>> introduce a format extension here.
>>
>> In particular, older versions would first explode unreachable objects
>> out of the cruft pack and into loose objects before expiring any of
>> them based on the loose object mtime. There is no risk here of causing
>> problems with older versions of Git and does not need an extension.
> 
> Surely when older and versions are acting on the same repository, they
> would fight by exploding out unreachable objects, packing them back
> into a cruft pack, etc, no?