On Sat, Jun 25, 2022 at 12:56 AM Junio C Hamano <gitster@xxxxxxxxx> wrote: > > Han Xin <hanxin.hx@xxxxxxxxxxxxx> writes: > > > If a commit is in the commit graph, we would expect the commit to also > > be present. > > > When we found the commit in the graph in lookup_commit_in_graph(), > > but the commit is missing from the repository, we will try > > promisor_remote_get_direct() and then enter another loop. While > > sometimes it will finally succeed because it cannot fork > > subprocess, > > Is that a mode of "succeed"-ing? Or merely a way to exit an endless > loop that does not make any progress with a failure? For the user, "fetch-pack" does succeed, because in deref_without_lazy_fetch(), even if lookup_commit_in_graph() fails to lazy fetch the lost commit, the following oid_object_info_extended() will help us complete the previous work. In a sense, this infinite loop is based on the fact that infinite processes can be created. However, your attempt to express the reasoning bellow is clearer. > > > it has exhausted the local process resources and can be harmful to the > > remote service. > > > > Signed-off-by: Han Xin <hanxin.hx@xxxxxxxxxxxxx> > > --- > > I think the single-liner change in the patch is a good one, but I am > having a hard time to agree with the reasoning above that explains > why it is a good change. > > Here is an attempt to express a reasoning I can understand, can > agree with, and (I think) better describes why the change is a good > one. Does my understanding of the problem and the solution totally > misses the mark? > > The commit-graph is used to opportunistically optimize > accesses to certain pieces of information on commit objects, > and lookup_commit_in_graph() tries to say "no" when the > requested commit does not locally exist by returning NULL, > in which case the caller can ask for (which may result in > on-demand fetching from a promisor remote) and parse the > commit object itself. > > However, it uses a wrong helper, repo_has_object_file(), to > do so. This helper not only checks if an object is > immediately available in the local object store, but also > tries to fetch from a promisor remote. But the fetch > machinery calls lookup_commit_in_graph(), thus causing an > infinite loop. > > We should make lookup_commit_in_graph() expect that a commit > given to it can be legitimately missing from the local > object store, by using the has_object_file() helper instead. > > > diff --git a/t/t5329-no-lazy-fetch-with-commit-graph.sh b/t/t5329-no-lazy-fetch-with-commit-graph.sh > > new file mode 100755 > > index 0000000000..4d25d2c950 > > --- /dev/null > > +++ b/t/t5329-no-lazy-fetch-with-commit-graph.sh > > Hmph, does this short-test need a completely new file? > > > @@ -0,0 +1,47 @@ > > +#!/bin/sh > > + > > +test_description='test for no lazy fetch with the commit-graph' > > + > > +. ./test-lib.sh > > + > > +test_expect_success 'setup: prepare a repository with a commit' ' > > + git init with-commit && > > + test_commit -C with-commit the-commit && > > + oid=$(git -C with-commit rev-parse HEAD) > > +' > > + > > +test_expect_success 'setup: prepare a repository with commit-graph contains the commit' ' > > + git init with-commit-graph && > > + echo "$(pwd)/with-commit/.git/objects" \ > > + >with-commit-graph/.git/objects/info/alternates && > > + # create a ref that points to the commit in alternates > > + git -C with-commit-graph update-ref refs/ref_to_the_commit "$oid" && > > + # prepare some other objects to commit-graph > > + test_commit -C with-commit-graph somthing && > > somthing? something? Nod. > > > + git -c gc.writeCommitGraph=true -C with-commit-graph gc && > > + test_path_is_file with-commit-graph/.git/objects/info/commit-graph > > +' > > + > > +test_expect_success 'setup: change the alternates to what without the commit' ' > > + git init --bare without-commit && > > + echo "$(pwd)/without-commit/objects" \ > > + >with-commit-graph/.git/objects/info/alternates && > > Doesn't this deliberately _corrupt_ the with-commit-graph repository > that depended on the object whose name is $oid in with-commit > repository? Do we require a corrupt repository to trigger the "bug"? > The "bug" depends on the commit exist in the commit-graph but missing in the repository. I didn't find a better way to make this kind of scene. This bug was first found when alternates and commit-graph were both used. Since the promise did not maintain all the references, I suspect that the "auto gc" during the update process of the promise caused the loss of the unreachable commits in the promise. > > + test_must_fail git -C with-commit-graph cat-file -e $oid > > +' > > + > > +test_expect_success 'setup: prepare another commit to fetch' ' > > + test_commit -C with-commit another-commit && > > + anycommit=$(git -C with-commit rev-parse HEAD) > > anycommit? another_commit? Be consistent in naming. > Nod. > > +' > > + > > +test_expect_success ULIMIT_PROCESSES 'fetch any commit from promisor with the usage of the commit graph' ' > > So we did all of the above set-up sequences only to skip the most > interesting test, if we were testing with "dash"? I suspect that it > may be cleaner to put the prerequisite to the whole file with the > "early test_done" trick like t0051 and t3008. > It make sense to me. Thanks. -Han Xin
