On 8/11/2020 7:36 AM, Abhishek Kumar wrote: > On Mon, Aug 10, 2020 at 12:42:29PM -0400, Derrick Stolee wrote: >> On 8/8/2020 10:53 PM, Abhishek Kumar via GitGitGadget wrote: >> >> ... >> >> Hm. So this scenario actually disables generation numbers completely >> in the event that anything in the chain disagrees. I think this is >> not the right way to approach the situation, as it will significantly >> punish users in this state with slow performance. >> >> The patch I sent [1] is probably better: it uses generation number >> v1 if the tip of the chain does not have a GDAT chunk. >> >> [1] https://lore.kernel.org/git/a3910f82-ab2e-bf35-ac43-c30d77f3c96b@xxxxxxxxx/ >> > > Yes, the patch is an clear improvement over my (convoluted and incorrect) > logic. Will add. > >> >> ... >> >> Please make a point to move the line that checks GIT_TEST_COMMIT_GRAPH_NO_GDAT >> from its current location to after this line. We want to make sure that the >> environment variable is checked _last_. The best location is likely the start >> of the implementation of compute_generation_numbers(), or immediately before >> the call to the method. >> > > Sure, will do. > >> >> ... >> >> It would be valuable to double-check here that the values in the GDAT chunk >> are correct. I'm concerned about the possibility that the 'generation' >> member of struct commit_graph_data gets filled with topological level during >> parsing and then that is written as an offset into the CDAT chunk. >> >> Perhaps this is best left for a follow-up series that updates the 'verify' >> subcommand to check the GDAT chunk. > > If I can understand it correctly, one of ways to update 'verify' > subcommand to check the GDAT chunk as well would to be make use of the > flag variable introduced in your patch. We can isolate generation number > related checks and run checks once with flag = 1 (checking corrected > commit dates) and once with flag = 0 (checking topological levels). > > This has the unfortunate effect of filling all commits twice, but as we > cannot change the commit_graph_data->generation any other way, I see no > alternatives without changing how commit_graph_generation() works. > > Would it make more sense if we add the flag to struct commit_graph > instead of making it depend solely on g->chunk_generation_data and set > it within parse_commit_graph()? > > We would be able to control the behavior of fill_commit_graph_info() and > we will not need to check g->chunk_generation_data before filling every > commit. I missed that you _already_ updated the logic in verify_commit_graph() based on the generation. That logic should catch the problem, so it might be enough to just add some "git commit-graph verify" commands into your multi-level tests. Specifically, the end result is this check: corrected_commit_date = commit_graph_generation(graph_commit); if (corrected_commit_date < max_parent_corrected_commit_date + 1) graph_report(_("commit-graph generation for commit %s is %"PRItime" < %"PRItime), oid_to_hex(&cur_oid), corrected_commit_date, max_parent_corrected_commit_date + 1); This will catch the order violations I was proposing could happen. It doesn't go the extra mile to ensure that the commit-graph stores the exact correct value or that the two bits of data are correct (both topo-level and corrected commit date). That is fine for now, and we can revisit if necessary. The diff below makes some tweaks to your split-level test to show the logic _was_ incorrect without my patch. Please incorporate the test changes into your series. Note in particular that I added a base layer that includes the GDAT chunk and _then_ adds a layer without the GDAT chunk. That is an important case! Thanks, -Stolee --- >8 --- diff --git a/commit-graph.c b/commit-graph.c index 17623274d9..d891a8ba3a 100644 --- a/commit-graph.c +++ b/commit-graph.c @@ -674,14 +674,6 @@ int generation_numbers_enabled(struct repository *r) if (!g->num_commits) return 0; - /* We cannot compare topological levels and corrected commit dates */ - while (g->base_graph) { - warning(_("commit-graph-chain contains mixed generation versions")); - if ((g->chunk_generation_data == NULL) ^ (g->base_graph->chunk_generation_data == NULL)) - return 0; - g = g->base_graph; - } - first_generation = get_be32(g->chunk_commit_data + g->hash_len + 8) >> 2; @@ -787,7 +779,7 @@ static void fill_commit_graph_info(struct commit *item, struct commit_graph *g, date_low = get_be32(commit_data + g->hash_len + 12); item->date = (timestamp_t)((date_high << 32) | date_low); - if (g->chunk_generation_data && (flags & COMMIT_GRAPH_GENERATION_V2)) + if (g->chunk_generation_data) graph_data->generation = item->date + (timestamp_t) get_be32(g->chunk_generation_data + sizeof(uint32_t) * lex_index); else diff --git a/t/t5324-split-commit-graph.sh b/t/t5324-split-commit-graph.sh index 1a9be5e656..721515cc23 100755 --- a/t/t5324-split-commit-graph.sh +++ b/t/t5324-split-commit-graph.sh @@ -443,6 +443,7 @@ test_expect_success 'setup repo for mixed generation commit-graph-chain' ' test_commit $i && git branch commits/$i || return 1 done && + git commit-graph write --reachable --split && git reset --hard commits/2 && for i in $(test_seq 6 10) do @@ -455,14 +456,15 @@ test_expect_success 'setup repo for mixed generation commit-graph-chain' ' git reset --hard commits/4 && git merge commits/6 && git branch merge/2 && - GIT_TEST_COMMIT_GRAPH_NO_GDAT=1 git commit-graph write --reachable --split && + GIT_TEST_COMMIT_GRAPH_NO_GDAT=1 git commit-graph write --reachable --split=no-merge && test-tool read-graph >output && cat >expect <<-EOF && - header: 43475048 1 1 3 0 - num_commits: 12 + header: 43475048 1 1 4 1 + num_commits: 7 chunks: oid_fanout oid_lookup commit_metadata EOF - test_cmp expect output + test_cmp expect output && + git commit-graph verify ' test_expect_success 'does not write generation data chunk if not present on existing tip' ' @@ -472,23 +474,25 @@ test_expect_success 'does not write generation data chunk if not present on exis git merge commits/5 && git merge merge/2 && git branch merge/3 && - git commit-graph write --reachable --split && + git commit-graph write --reachable --split=no-merge && test-tool read-graph >output && cat >expect <<-EOF && header: 43475048 1 1 4 1 num_commits: 3 chunks: oid_fanout oid_lookup commit_metadata EOF - test_cmp expect output + test_cmp expect output && + git commit-graph verify ' test_expect_success 'writes generation data chunk when commit-graph chain is replaced' ' cd "$TRASH_DIRECTORY/mixed" && - git commit-graph write --reachable --split='replace' && + git commit-graph write --reachable --split=replace && test_path_is_file $graphdir/commit-graph-chain && test_line_count = 1 $graphdir/commit-graph-chain && verify_chain_files_exist $graphdir && - graph_read_expect 15 + graph_read_expect 15 && + git commit-graph verify ' test_done
