Re: What's cooking in git.git (May 2025, #07; Fri, 23)

From: Justin Tobler <jltobler@gmail.com>
Date: May 27, 2025, 19:45 UTC
Message-ID: <shpx4piigp5sqgpbzx4vdgu4zdn7z3ykxhu2cdyjh5vpr6zbqb@rf2sxg6hukpd>
In-Reply-To: <xmqqtt56ov4k.fsf@gitster.g>

On 25/05/27 09:50AM, Junio C Hamano wrote:

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> Patrick Steinhardt <ps@pks.im> writes:
> > I think the only outstanding discussion is whether to name things
> > `odb_alternate` or `odb_source` [1]. In case others agree that
> > `odb_source` is a better name I'm happy to revise, but if not I'd rather
> > keep it as-is.
> 
> The model in which the term "alternates" was born is "A repository
> has its own object directory, the primary one, and in addition it
> can borrow from zero or more alternate object directories that are
> used by other repositories".  The presence of the primary makes the
> word "alternate" meaningful.
> 
> Is the model now "A repository has one object store, which consists
> of one or more X, all of which are equals"?  If there is no primary
> that is more special than others, then calling X an "alternate" may
> indeed sound funny, although (1) I do not find it terribly confusing
> and (2) I do not find "source" much better, either.

My understanding is that the object store still has a primary X and zero or more alternative X. The idea is that eventually, with pluggable ODBs, X can be a different backend/provider instead of just being "files". If this is the case, calling X an "alternate" would mean we have a primary "alternate" and potentially a set of "alternate" alternates.

This sounds a bit odd and doesn't quite match what I would intuitively expect. But, I also don't find it super confusing either.

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> The names we use to call the collection and the underlying
> implementations of the collection in the reference world
> unfortunately does not quite help to guide us, as we do not take two
> implementations and compose into one unified view, which is what we
> are doing in the object store.  Hmmm...

Similar to references, I still think of a pluggable ODB as a "backend". The main difference being that with references there is only a single backend active ("file" or "reftables") at a time, while for the object store there could be multiple.

-Justin

> We call pathspec elements given on the command line collectively a
> pathspec.  "Object store elements like loose object directories and
> packfiles form the object store"?  That may be a mouthful.  I dunno.