On Fri, Mar 04, 2022 at 09:03:15AM -0500, Derrick Stolee wrote: > On 3/3/2022 11:00 AM, Derrick Stolee wrote: > > On 3/3/2022 6:19 AM, Patrick Steinhardt wrote: > >> On Wed, Mar 02, 2022 at 09:57:17AM -0500, Derrick Stolee wrote: > >>> On 3/2/2022 8:57 AM, Patrick Steinhardt wrote: > >>>> On Tue, Mar 01, 2022 at 10:25:46AM -0500, Derrick Stolee wrote: > >>>>> On 3/1/2022 9:53 AM, Patrick Steinhardt wrote: > >>> > >>>>>> Hum. I have re-verified, and this indeed seems to play out. So I must've > >>>>>> accidentally ran all my testing with the state generated without the > >>>>>> final patch which fixes the corruption. I do see lots of the following > >>>>>> warnings, but overall I can verify and write the commit-graph just fine: > >>>>>> > >>>>>> commit-graph generation for commit c80a42de8803e2d77818d0c82f88e748d7f9425f is 1623362063 < 1623362139 > >>>>> > >>>>> But I'm not able to generate these warnings from either version. I > >>>>> tried generating different levels of a split commit-graph, but > >>>>> could not reproduce it. If you have reproduction steps using current > >>>>> 'master' (or any released Git version) and the four patches here, > >>>>> then I would love to get a full understanding of your errors. > >>>>> > >>>>> Thanks, > >>>>> -Stolee > >>>> > >>>> I haven't yet been able to reproduce it with publicly available data, > >>>> but with the internal references I'm able to evoke the warnings > >>>> reliably. It only works when I have two repositories connected via > >>>> alternates, when generating the commit-graph in the linked-to repo > >>>> first, and then generating the commit-graph in the linking repo. > >>>> > >>>> The following recipe allows me to reproduce, but rely on private data: > >>>> > >>>> $ git --version > >>>> git version 2.35.1 > >>>> > >>>> # The pool repository is the one we're linked to from the fork. > >>>> $ cd "$pool" > >>>> $ rm -rf objects/info/commit-graph objects/info/commit-graph > >>>> $ git commit-graph write --split > >>>> > >>>> $ cd "$fork" > >>>> $ rm -rf objects/info/commit-graph objects/info/commit-graph > >>>> $ git commit-graph write --split > >>>> > >>>> $ git commit-graph verify --no-progress > >>>> $ echo $? > >>>> 0 > >>>> > >>>> # This is 715d08a9e51251ad8290b181b6ac3b9e1f9719d7 with your full v2 > >>>> # applied on top. > >>>> $ ~/Development/git/bin-wrappers/git --version > >>>> git version 2.35.1.358.g7ede1bea24 > >>>> > >>>> $ ~/Development/git/bin-wrappers/git commit-graph verify --no-progress > >>>> commit-graph generation for commit 06a91bac00ed11128becd48d5ae77eacd8f24c97 is 1623273624 < 1623273710 > >>>> commit-graph generation for commit 0ae91029f27238e8f8e109c6bb3907f864dda14f is 1622151146 < 1622151220 > >>>> commit-graph generation for commit 0d4582a33d8c8e3eb01adbf564f5e1deeb3b56a2 is 1631045222 < 1631045225 > >>>> commit-graph generation for commit 0daf8976439d7e0bb9710c5ee63b570580e0dc03 is 1620347739 < 1620347789 > >>>> commit-graph generation for commit 0e0ee8ffb3fa22cee7d28e21cbd6df26454932cf is 1623783297 < 1623783380 > >>>> commit-graph generation for commit 0f08ab3de6ec115ea8a956a1996cb9759e640e74 is 1621543278 < 1621543339 > >>>> commit-graph generation for commit 133ed0319b5a66ae0c2be76e5a887b880452b111 is 1620949864 < 1620949915 > >>>> commit-graph generation for commit 1341b3e6c63343ae94a8a473fa057126ddd4669a is 1637344364 < 1637344384 > >>>> commit-graph generation for commit 15bdfc501c2c9f23e9353bf6e6a5facd9c32a07a is 1623348103 < 1623348133 > >>>> ... > >>>> $ echo $? > >>>> 1 > >>>> > >>>> When generating commit-graphs with your patches applied the `verify` > >>>> step works alright. > >>>> > >>>> I've also by accident stumbled over the original error again: > >>>> > >>>> fatal: commit-graph requires overflow generation data but has none > >>>> > >>>> This time it's definitely not caused by generating commit-graphs with an > >>>> in-between state of your patch series because the data comes straight > >>>> from production with no changes to the commit-graphs performed by > >>>> myself. There we're running Git v2.33.1 with a couple of backported > >>>> patches (see [1]). While those patches cause us to make more use of the > >>>> commit-graph, none modify the way we generate them. > >>>> > >>>> Of note is that the commit-graph contains references to commits which > >>>> don't exist in the ODB anymore. > >>>> > >>>> Patrick > >>>> > >>>> [1]: https://gitlab.com/gitlab-org/gitlab-git/-/commits/pks-v2.33.1.gl3 > >>> > >>> Thank you for your diligence here, Patrick. I really appreciate the > >>> work you're putting in to verify the situation. > >>> > >>> Since our repro relies on private information, but is consistent, I > >>> wonder if we should take the patch below, which starts to ignore the > >>> older generation number v2 data and only writes freshly-computed > >>> numbers. > >>> > >>> Thanks, > >>> -Stolee > >> > >> Thanks. With your patch below the `fatal:` error is gone, but I'm still > >> seeing the same errors with regards to the commit-graph generations. > > > > This is disappointing and unexpected. Thanks for verifying. > > > >> So to summarize my findings: > >> > >> - This bug occurs when writing commit-graphs with v2.35.1, but > >> reading them with your patches. > >> > >> - This bug occurs when I have two repositories connected via an > >> alternates file. I haven't yet been able to reproduce it in a > >> single repository that is not connected to a separate ODB. > > > > This is an interesting distinction. One that I didn't think would > > matter, but I'll look into the code to see how that could affect > > things. > > > >> - This bug only occurs when I first generate the commit-graph in the > >> repository I'm borrowing objects from. > >> > >> - This bug only occurs when I write commit-graphs with `--split` in > >> both repositories. "Normal" commit-graphs don't have this issue, > >> and neither can I see it with `--split=replace` or mixed-type > >> commit-graphs. > >> > >> Beware, the following explanation is based on my very basic > >> understanding of the commit-graph code and thus more likely to be wrong > >> than right: > >> > >> With the old Git version, we've been mis-parsing the generation because > >> `read_generation_data` wasn't ever set. As a result it can happen that > >> the second split commit-graph we're generating computes its own > >> generation numbers from the wrong starting point because it uses the > >> mis-parsed generation numbers from the parent commit-graph. > >> > >> With your patches, we start to correctly account for overflows and would > >> thus end up with a different value for the generation depending on where > >> we parse the commit from: if we parse it from the first commit-graph it > >> would be correct because it's contains the "root" of the generation > >> numbers. But if we parse a commit from the second commit-graph we may > >> have a mismatch because the generation numbers in there may have been > >> derived from generation numbers mis-parsed from the first commit-graph. > >> And because these would be wrong in case there was an overflow it is > >> clear that the new corrected generation number may be wrong, as well. > > > > Hm. My expectation was that the older layers of the split commit-graph > > would have read_generation_data disabled (because the new Git version > > cannot read the GDAT chunk) and then the validate_mixed_generation_chain() > > method would remove read_generation_data from all of the graphs in the > > list. > > > > Combining this with your thoughts on cross-alternate split commit-graphs, > > this makes me think we should try this: > > > > --- >8 --- > > > > diff --git a/commit-graph.c b/commit-graph.c > > index fb2ced0bd6..74c6534f56 100644 > > --- a/commit-graph.c > > +++ b/commit-graph.c > > @@ -609,8 +609,6 @@ struct commit_graph *read_commit_graph_one(struct repository *r, > > if (!g) > > g = load_commit_graph_chain(r, odb); > > > > - validate_mixed_generation_chain(g); > > - > > return g; > > } > > > > @@ -668,7 +666,13 @@ static int prepare_commit_graph(struct repository *r) > > !r->objects->commit_graph && odb; > > odb = odb->next) > > prepare_commit_graph_one(r, odb); > > - return !!r->objects->commit_graph; > > + > > + if (r->objects->commit_graph) { > > + validate_mixed_generation_chain(r->objects->commit_graph); > > + return 1; > > + } > > + > > + return 0; > > } > > > > int generation_numbers_enabled(struct repository *r) > > > > > > --- >8 --- > > > > Notice that I'm moving the validate_mixed_generation_chain() call > > out of read_commit_graph_one() and into prepare_commit_graph(). To > > my understanding, this _should_ have an equivalent end state as the > > old code, but might be worth trying just as a quick check. > > > > I will continue investigating and try to reproduce with this > > additional constraint of working across an alternate. > > My attempts to reproduce this across an alternate have failed. I > tried running the following test against Git without these patches, > then verify with the newer version of Git. (I also have generated > a few new layers on top with these patches, and they correctly drop > the GDA2 and GDO2 chunks when the lower layers "don't have gen v2".) > > > test_description='commit-graph with offsets across alternates' > . ./test-lib.sh > > if ! test_have_prereq TIME_IS_64BIT || ! test_have_prereq TIME_T_IS_64BIT > then > skip_all='skipping 64-bit timestamp tests' > test_done > fi > > > UNIX_EPOCH_ZERO="@0 +0000" > FUTURE_DATE="@4147483646 +0000" > > GIT_TEST_COMMIT_GRAPH_CHANGED_PATHS=0 > > test_expect_success 'generate alternate split commit-graph' ' > git init alternate && > ( > cd alternate && > test_commit --date "$UNIX_EPOCH_ZERO" 1 && > test_commit --date "$FUTURE_DATE" 2 && > git commit-graph write --reachable && > test_commit --date "$UNIX_EPOCH_ZERO" 3 && > test_commit --date "$FUTURE_DATE" 4 && > git commit-graph write --reachable --split=no-merge > ) && > git clone --shared alternate fork && > ( > cd fork && > test_commit --date "$UNIX_EPOCH_ZERO" 5 && > test_commit --date "$FUTURE_DATE" 6 && > git commit-graph write --reachable --split=no-merge && > test_commit --date "$UNIX_EPOCH_ZERO" 7 && > test_commit --date "$FUTURE_DATE" 8 && > git commit-graph write --reachable --split=no-merge > ) > ' > > test_done > > > My testing after running this with -d allows me to reliably see these > layers being created with GDAT and GDOV chunks. Running the 'git > commit-graph verify' command with the new code does not show those > errors, even after adding commits and another layer to the split > commit-graph. > > I look forward to any additional insights you might have here. I don't really know why, but now I've become unable to reproduce it again. I think we should just go with your patch 5/4 on top -- it does fix the most important issue, which is the `die()` I saw on almost all commands. The second part about the warnings I'm just not sure about, but I don't think it should stop this patch series given my own uncertainty. Patrick
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