Re: [PATCH] experimental: default to fetch.writeCommitGraph=false

[Taylor Blau <me@ttaylorr.com>]

Hi Junio,

On Tue, Jul 07, 2020 at 08:09:36AM -0700, Junio C Hamano wrote:
> Jonathan Nieder <jrnieder@gmail.com> writes:
>
> > The fetch.writeCommitGraph feature makes fetches write out a commit
>
> > In other words:
> >
> > - this patch only affects behavior with feature.experimental=true
> >
> > - it makes feature.experimental match the configuration Google has
> >   been using for the last few months, meaning it would leave users in
> >   a better tested state than without it
> >
> > - this should improve testing for other features guarded by
> >   feature.experimental, by making feature.experimental safer to use
>
>
> In other words, fetch.writeCommitGraph in its current form is too
> broken to be recommended even for brave souls with "experimental"
> bit on.
>
> I wonder if we perhaps wnat to add to the documentation for
> writeCommitGraph configuration that its use is currently not
> recommended in a shallow clone or something (I know it is not
> a problem just to use it with shallow but the breakage needs
> to involve unshallowing, but by definition those who do not
> use shallow would not hit the unshallowing bug, so...).

I think this is a good direction if you don't want to take the patch I
sent in [1] for v2.28.0. If you do, though, I don't think that this
would be necessary.

> > Reported-by: Jay Conrod <jayconrod@google.com>
> > Helped-by: Taylor Blau <me@ttaylorr.com>
> > Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
> > ---
> > I realize this is late to send.  That said, as described above, I
> > think it's a good way to buy time by minimizing user exposure to
> > fetch.writeCommitGraph=true until a fix for it is well cooked.
> >
> > In other words, I'd like to see this patch in Git 2.28-rc0.
>
> Yes, I do, too.
>
> Thanks.
>
> > diff --git a/Documentation/config/fetch.txt b/Documentation/config/fetch.txt
> > index b1a9b1461d3..b20394038d1 100644
> > --- a/Documentation/config/fetch.txt
> > +++ b/Documentation/config/fetch.txt
> > @@ -90,5 +90,4 @@ fetch.writeCommitGraph::
> >  	the existing commit-graph file(s). Occasionally, these files will
> >  	merge and the write may take longer. Having an updated commit-graph
> >  	file helps performance of many Git commands, including `git merge-base`,
> > -	`git push -f`, and `git log --graph`. Defaults to false, unless
> > -	`feature.experimental` is true.
> > +	`git push -f`, and `git log --graph`. Defaults to false.
> > diff --git a/repo-settings.c b/repo-settings.c
> > index dc6817daa95..0918408b344 100644
> > --- a/repo-settings.c
> > +++ b/repo-settings.c
> > @@ -51,14 +51,14 @@ void prepare_repo_settings(struct repository *r)
> >  		UPDATE_DEFAULT_BOOL(r->settings.index_version, 4);
> >  		UPDATE_DEFAULT_BOOL(r->settings.core_untracked_cache, UNTRACKED_CACHE_WRITE);
> >  	}
> > +
> >  	if (!repo_config_get_bool(r, "fetch.writecommitgraph", &value))
> >  		r->settings.fetch_write_commit_graph = value;
> > -	if (!repo_config_get_bool(r, "feature.experimental", &value) && value) {
> > -		UPDATE_DEFAULT_BOOL(r->settings.fetch_negotiation_algorithm, FETCH_NEGOTIATION_SKIPPING);
> > -		UPDATE_DEFAULT_BOOL(r->settings.fetch_write_commit_graph, 1);
> > -	}
> >  	UPDATE_DEFAULT_BOOL(r->settings.fetch_write_commit_graph, 0);
> >
> > +	if (!repo_config_get_bool(r, "feature.experimental", &value) && value)
> > +		UPDATE_DEFAULT_BOOL(r->settings.fetch_negotiation_algorithm, FETCH_NEGOTIATION_SKIPPING);
> > +
> >  	/* Hack for test programs like test-dump-untracked-cache */
> >  	if (ignore_untracked_cache_config)
> >  		r->settings.core_untracked_cache = UNTRACKED_CACHE_KEEP;

Thanks,
Taylor

[1]: https://lore.kernel.org/git/20200707144338.GA26342@syl.lan/T/#t