Re: [PATCH v2 6/9] index-format: update preamble to cached tree extension

Derrick Stolee [off-list ref] writes:

quoted

We later found out that we rather often compare the index against
the tree of HEAD (think: "git status"), and diff-lib.c::diff_cache()
does take advantage of the fact that an entire directory can be
skipped if the tree object taken from the HEAD side exactly matches
the tree recorded for the subdirectory in the cache tree extension.

I need to read more about this. traverse_by_cache_tree() seems to
be a good place to start. Thanks.

Ah, that one I forgot about.

What I had in mind was a different optimization that is far more
aggressive in unpack-trees.c::unpack_callback(); look for a comment
that begins with "Everything under the name matches".  The block
allows us to skip an entire subdirectory hierarchy.