I took a look at webgit, and it looks like at least for the "projects" page, the most common operation ends up being basically
git-rev-list --header --parents --max-count=1 HEAD
Now, the thing is, the way "git-rev-list" works, it always keeps on popping the parents and parsing them in order to build the list of parents, and it turns out that even though we just want a single commit, git-rev-list will invariably look up _three_ generations of commits.
It will parse: - the commit we want (it obviously needs this) - it's parent(s) as part of the "pop_most_recent_commit()" logic - it will then pop one of the parents before it notices that it doesn't need any more - and as part of popping the parent, it will parse the grandparent (again due to "pop_most_recent_commit()".
Now, I've strace'd it, and it really is pretty efficient on the whole, but if things aren't nicely cached, and with long-latency IO, doing those two extra objects (at a minimum - if the parent is a merge it will be more) is just wasted time, and potentially a lot of it.
So here's a quick special-case for the trivial case of "just one commit, and no date-limits or other special rules".
Signed-off-by: Linus Torvalds <email@example.com> Signed-off-by: Junio C Hamano <firstname.lastname@example.org>