Re: [PATCH v3 2/3] shallow: offer to prune only non-existing entries

From: Johannes Schindelin <johannes.schindelin@gmx.de>
Date: Oct 29, 2018, 20:45 UTC
Message-ID: <nycvar.QRO.7.76.6.1810292047130.4546@tvgsbejvaqbjf.bet>
In-Reply-To: <20181026204914.134946-1-jonathantanmy@google.com>

Hi Jonathan,

On Fri, 26 Oct 2018, Jonathan Tan wrote:

Show 9 quoted lines

> > So even better would be to use `is_promisor_object(oid) ||
> > has_object_file(oid)`, right?
> > 
> > This is something that is probably not even needed: as I mentioned,
> > the shallow commits are *expected* to be local. It should not ever
> > happen that they are fetched.
> 
> That would help, but I don't think it would help in the "fast-forward
> from A to B where A is B's parent" case I describe in [1].

I don't think that that analysis is correct. It assumes that there could be a promised commit that is also listed as shallow. I do not think that is a possible scenario.

And even if it were, why would asking for a promised commit object download not only that object but also all of its trees and all of its ancestors? That's not how I understood the idea of the lazy clone: I understood promised objects to be downloaded on demand, individually.

Show 9 quoted lines

> My suggestion was:
> 
> > It sounds safer to me to use the fast approach in this patch when the
> > repository is not partial, and stick to the slow approach when it is.
> 
> which can be done by replacing "prune_shallow(0, 1)" in patch 3 with
> "prune_shallow(0, !repository_format_partial_clone)", possibly with a comment
> that the fast method checks object existence for each shallow line directly,
> which is undesirable when the repository is a partial clone.

I am afraid that that would re-introduce the bug pointed out by Peff: you *really* would need to traverse all reachable commits to use the non-fast pruning method. And we simply don't.

Ciao, Dscho

Show 5 quoted lines

> (repository_format_partial_clone is non-NULL with the name of the promisor
> remote if the repository is a partial clone, and NULL otherwise).
> 
> [1] https://public-inbox.org/git/20181025185459.206127-1-jonathantanmy@google.com/
>