Is Git's commit atomic?

Question

An update hook can reject parts of a commit and allow others.

update() in receive_pack.c runs in a loop which then calls the update hook possibly multiple times during a commit. Each time the update hook is called, it can return failure, seemingly allowing some refs to be updated and some not updated if rejected.

Does Git's feature of an update hook allowing possibly part of a commit to succeed and some fail mean that Git's commit is not atomic?

Or what am I missing here? Thanks.

Answer 1

Yes commits are atomic. It is not possible to reject part of a commit.

The update hook may be called multiple times during a single push (not commit) if multiple branches are being pushed at the same time. This allows accepting updates to some branches while rejecting updates to others, but each accepted update will still point to a complete commit from the pushing repository.