Re: [PATCH] builtin/pack-objects.c: introduce `pack.extraCruftTips`

From: Taylor Blau <me@ttaylorr.com>
Date: Apr 20, 2023, 19:30 UTC
Message-ID: <ZEGSvfEkE5PhokKv@nand.local>
In-Reply-To: <xmqqzg72zalp.fsf@gitster.g>

On Thu, Apr 20, 2023 at 11:12:34AM -0700, Junio C Hamano wrote:

Show 12 quoted lines

> Taylor Blau <me@ttaylorr.com> writes:
>
> > This patch introduces a new configuration, `pack.extraCruftTips` which
> > allows the caller to specify a program (or set of programs) whose output
> > is treated as a set of objects to treat as "kept", even if they are
> > unreachable and have aged out of the retention period.
>
> I can see why this would make the implementation simpler, simply
> because no existing codepaths that determines if an object is still
> live knows about such a program hence all the codepaths by default
> keep considering them expungeable crufts except for a very limited
> set of codepaths that will pay attention to the program.

Right, this is about band-aiding a situation where there are objects that we want to save for whatever reason but which do not (need to) be reachable via any reference(s).

> But it makes me wonder if it would make the life of end-users simpler
> if we reserve a special ref hierarchy, say "refs/crufts/*", than
> having to write a program for doing something like this.

Ideally, yes. But I think there are certain instances where there are far too many (disconnected) objects that creating a reference for each part of the unreachable object graph that we want to keep is infeasible.

Another way to think about pack.extraCruftTips is that the program invocation is acting like the refs/crufts hierarchy would if it existed, but without actually having to write all of those references down.

Thanks, Taylor