How to save index with "cache tree" extension?

Hello,

I have a project with approx 2000 files stored on NFS partition. When I initialize repository with pygit2 all subsequent commits took about 5sec. But after I commit anything (even empty tree) via git subsequent commits via pygit2 took only 0.5sec. This is because commit via git writes cache tree (https://git-scm.com/docs/index-format#_cache_tree) extension to .git/index file.

Finally I found that reading tree back to the index builds internal "cache tree". And now I wondering if this is a correct way to buid cache tree on initial commit?

repo = pygit2.init_repository(path, bare=False, flags=pygit2.GIT_REPOSITORY_INIT_NO_REINIT)
index = repo.index
index.add_all()
tree_id = index.write_tree()
# NOTE: Adds "cache tree" extension to the index.
index.read_tree(tree_id)
index.write()
repo.create_commit("HEAD", SIGNATURE, SIGNATURE, "Inital commit", tree_id, [])

Inizia con le chiamate a pygit2.init_repository, index.add_all(), index.write_tree(), index.read_tree(), index.write() e repo.create_commit() mostrate nell’issue, quindi esamina come vengono gestite le index extensions. Confronta l’indice risultante con uno prodotto da git in un repository con molti file. Il lavoro è completato quando viene stabilito se cache tree è supportato e viene documentato o corretto il comportamento del commit iniziale.