Re: [PATCH v5 1/4] gitformat-commit-graph: describe version 2 of BDAT

Taylor Blau [off-list ref] writes:

This is a little beyond the scope of your series, but since we're
changing the on-disk format here a little bit, I think that it might be
worth it to consider whether there are any other changes that we'd like
to perform at the same time.

One that comes to mind is serializing the `max_changed_paths` value of
the Bloom filter settings, which is currently hard-coded as a constant,
c.f. 97ffa4fab50 (commit-graph.c: store maximum changed paths,
2020-09-17).

We always assume that the value there is 512, or the environment
variable GIT_TEST_BLOOM_SETTINGS_MAX_CHANGED_PATHS, if it is set. But it
might be nice to write it to disk, since it would allow us to do
something like:

That's true...I do think it makes sense to either have both
bits_per_entry and max_changed_paths (because if we are reusing Bloom
filters when writing, presumably we would want to make sure that the
existing ones were generated using the same settings), or have neither
(since we don't need them for reading).

Having said that, I am inclined to not change this, so that the offset
calculations are the same for both versions (e.g. in the test tool
too), and as far as I know, we haven't had problems with this. But I can
change it if people want.

quoted

+	in Probabilistic Verification". Version 1 Bloom filters have a bug that appears
+	when char is signed and the repository has path names that have characters >=
+	0x80; Git supports reading and writing them, but this ability will be removed
+	in a future version of Git.

Makes sense.

Thanks,
Taylor

Thanks for taking a look.