Re: [PATCH] list-objects: don't queue root trees unless revs->tree_objects is set

[Jeff King <peff@peff.net>]

On Thu, Sep 12, 2019 at 09:52:53AM -0700, Junio C Hamano wrote:

> Jeff King <peff@peff.net> writes:
> 
> >> I was surprised we ever called repo_get_commit_tree() at all, since
> >> we're literally just traversing commits here. It looks like
> >> list-objects.c is very happy to queue pending trees for each commit,
> >> even if we're just going to throw them away when we get to
> >> process_tree()! I wonder if could be checking revs->tree_objects here
> >> and saving ourselves some work.
> >
> > Indeed, this seems to help quite a bit in the commit-graph case. I think
> > it's worth doing (and is independent of the other patch).
> 
> Yeah, I agree this is very much worth doing and is orthogonal to the
> other one.
> 
> Thanks for spotting it.  I wonder if it was broken like this forever
> since the beginning X-<.

Not quite since the beginning; it comes from 8d2dfc49b1
(process_{tree,blob}: show objects without buffering, 2009-04-10). I
suspect nobody noticed because the cost for the normal case is really
just shuffling some pointers around. It's only because it actively works
against the commit-graph optimizations that it's so expensive there.

I was surprised (and pleased) by how much such a simple thing helped.

-Peff