Re: [PATCH 07/15] commit-graph: new filter ver. that fixes murmur3

[Taylor Blau <me@ttaylorr.com>]

On Mon, Oct 09, 2023 at 12:52:13PM -0700, Junio C Hamano wrote:
> Taylor Blau <me@ttaylorr.com> writes:
>
> > However, I am not entirely sure I agree with you that this is a "new"
> > issue. At least in the sense that Git (on 'master') does not currently
> > know how to deal with Bloom filters that have different settings across
> > commit-graph layers.
> >
> > IOW, you could produce this problem today using the test you wrote in
> > <20201015132147.GB24954@szeder.dev> using different values of the
> > GIT_BLOOM_SETTINGS environment variables as a proxy for different values
> > of the commitGraph.changedPathsVersion configuration variable introduced
> > in this series.
> >
> > So I think that this series makes it easier to fall into that trap, but
> > the trap itself is not new. I think a reasonable stopgap (which IIUC you
> > have suggested earlier) is to prevent writing a new commit-graph layer
> > with a different hash version than the previous layer.
>
> What we probably want more urgently than that stopgap is to perhaps
> teach the code pretend as if commit-graph did not exist when we
> detect multiple layers use different hash versions (or perhaps only
> use the base layer and ignore the rest as an anti-pessimization), to
> protect correctness first, no?

Very good suggestion, thanks.

Thanks,
Taylor