> As a general rule (and why I'm raising this issue in reply to Jonathan's
> patch), I think most or all sites that want OBJECT_INFO_QUICK will want
> SKIP_FETCH_OBJECT as well, and vice versa. The reasoning is generally
> the same:
>
> - it's OK to racily have a false negative (we'll still be correct, but
> possibly a little less optimal)
>
> - it's expected and normal to be missing the object, so spending time
> double-checking the pack store wastes measurable time in real-world
> cases
I took a look on "next" and it's true for these reasons in most cases
but not all.
QUICK implies SKIP_FETCH_OBJECT:
fetch-pack.c: Run with fetch_if_missing=0 (from builtin/fetch.c,
builtin/fetch-pack.c, or through a lazy fetch) so OK.
builtin/index-pack.c: Run with fetch_if_missing=0, so OK.
builtin/fetch.c: Run with fetch_if_missing=0, so OK.
object-store.h, sha1-file.c: Definition and implementation of this
flag.
Everything is OK here. Now, SKIP_FETCH_OBJECT implies QUICK:
cache-tree.c: I added this recently in f981ec18cf ("cache-tree: do not
lazy-fetch tentative tree", 2019-09-09). No problem with a false
negative, since we know how to reconstruct the tree. OK.
object-store.h, sha1-file.c: Definition and implementation of this
flag.
send-pack.c: This patch (which is already in "next"). If we have a
false negative, we might accidentally send more than we need. But that
is not too bad.
promisor-remote.c: This is the slightly tricky one. We use this
information to determine if we got our lazily-fetched object from the
most recent lazy fetch, or if we should continue attempting to fetch the
given object from other promisor remotes; so this information is
important. However, adding QUICK doesn't lose us anything because the
lack of QUICK only helps us when there is another process packing
loose objects: if we got our object, our object will be in a pack
(because of the way the fetch is implemented - in particular, we need
a pack because we need the ".promisor" file).
So everything is OK except for promisor-remote.c, but even that is OK
for another reason.
Having said that, perhaps we should consider promisor-remote.c as
low-level code and expect it to know that objects are fetched into a
packfile (as opposed to loose objects), so it can safely use QUICK
(which is documented as checking packed after packed and loose). If no
one disagrees, I can make such a patch after jt/push-avoid-lazy-fetch is
merged to master (as is the plan, according to What's Cooking [1]).
[1] https://public-inbox.org/git/xmqq8sprhgzc.fsf@xxxxxxxxxxxxxxxxxxxxxxxxx/
