Re: [PATCH v2 0/4] [RFC] repack: add --filter=

> On Mon, Feb 21, 2022 at 10:10:15PM +0100, Christian Couder wrote:
>>>> Also, to have more protection we can either
>>>>
>>>> 1. add a config value that needs to be set to true for repack to remove
>>>> objects (repack.allowDestroyFilter).
>>
>> I don't think it's of much value. We don't have such config values for
>> other possibly destructive operations.
>>
>>>> 2. --filter is dry-run by default and prints out objects that would have been removed,
>>>> and it has to be combined with another flag --destroy in order for it to actually remove
>>>> objects from the odb.
>>
>> I am not sure it's of much value either compared to naming it
>> --filter-destroy. It's likely to just make things more difficult for
>> users to understand.
>
> On this and the above, I agree with Christian.
>
>>> I share the same concern as Robert and Stolee do. But I think this issue
>>> goes deeper than just naming.
>>>
>>> Even if we called this `git repack --delete-filter` and only ran it with
>>> `--i-know-what-im-doing` flag, we would still be leaving repository
>>> corruption on the table, just making it marginally more difficult to
>>> achieve.
>>
>> My opinion on this is that the promisor object mechanism assumes by
>> design that some objects are outside a repo, and that this repo
>> shouldn't care much about these objects possibly being corrupted.
>
> For what it's worth, I am fine having a mode of repack which allows us
> to remove objects that we know are stored by a promisor remote. But this
> series doesn't do that, so users could easily run `git repack -d
> --filter=...` and find that they have irrecoverably corrupted their
> repository.
>
> I think that there are some other reasonable directions, though. One
> which Robert and I discussed was making it possible to split a
> repository into two packs, one which holds objects that match some
> `--filter` criteria, and one which holds the objects that don't match
> that filter.
>
> Another option would be to prune the repository according to objects
> that are already made available by a promisor remote.

>
> An appealing quality about the above two directions is that the first
> doesn't actually remove any objects, just makes it easier to push a
> whole pack of unwanted objects off to a promsior remote. The second
> prunes the repository according to objects that are already made
> available by the promisor remote. (Yes, there is a TOCTOU race there,
> too, but it's the same prune-while-pushing race that Git already has
> today).
>
>> I am not against a name and some docs that strongly state that users
>> should be very careful when using such a command, but otherwise I
>> think such a command is perfectly ok. We have other commands that by
>> design could lead to some objects or data being lost.
>
> I can think of a handful of ways to remove objects which are unreachable
> from a repository, but I am not sure we have any ways to remove objects
> which are reachable.
>
>>> But as it stands right now, I worry that this feature is too easily
>>> misused and could result in unintended repository corruption.
>>
>> Are you worrying about the UI or about what it does?
>>
>> I am ok with improving the UI, but I think what it does is reasonable.
>
> I am more worried about the proposal's functionality than its UI,
> hopefully my concerns there are summarized above.
>
> Thanks,
> Taylor