The fetch.writeCommitGraph feature makes fetches write out a commit graph file for the newly downloaded pack on fetch. This improves the performance of various commands that would perform a revision walk and eventually ought to be the default for everyone. To prepare for that future, it's enabled by default for users that set feature.experimental=true to experience such future defaults. Alas, for --unshallow fetches from a shallow clone it runs into a snag: by the time Git has fetched the new objects and is writing a commit graph, it has performed a revision walk and r->parsed_objects contains information about the shallow boundary from *before* the fetch. The commit graph writing code is careful to avoid writing a commit graph file in shallow repositories, but the new state is not shallow, and the result is that from that point on, commands like "git log" make use of a newly written commit graph file representing a fictional history with the old shallow boundary. We could fix this by making the commit graph writing code more careful to avoid writing a commit graph that could have used any grafts or shallow state, but it is possible that there are other pieces of mutated state that fetch's commit graph writing code may be relying on. So disable it in the feature.experimental configuration. Google developers have been running in this configuration (by setting fetch.writeCommitGraph=false in the system config) to work around this bug since it was discovered in April. Once the fix lands, we'll enable fetch.writeCommitGraph=true again to give it some early testing before rolling out to a wider audience. In other words: - this patch only affects behavior with feature.experimental=true - it makes feature.experimental match the configuration Google has been using for the last few months, meaning it would leave users in a better tested state than without it - this should improve testing for other features guarded by feature.experimental, by making feature.experimental safer to use Reported-by: Jay Conrod <jayconrod@xxxxxxxxxx> Helped-by: Taylor Blau <me@xxxxxxxxxxxx> Signed-off-by: Jonathan Nieder <jrnieder@xxxxxxxxx> --- I realize this is late to send. That said, as described above, I think it's a good way to buy time by minimizing user exposure to fetch.writeCommitGraph=true until a fix for it is well cooked. In other words, I'd like to see this patch in Git 2.28-rc0. Thanks of all kinds welcome, as always. Previous discussion: https://lore.kernel.org/git/20200603034213.GB253041@xxxxxxxxxx/ Documentation/config/feature.txt | 8 -------- Documentation/config/fetch.txt | 3 +-- repo-settings.c | 8 ++++---- 3 files changed, 5 insertions(+), 14 deletions(-) diff --git a/Documentation/config/feature.txt b/Documentation/config/feature.txt index 28c33602d52..c0cbf2bb1cd 100644 --- a/Documentation/config/feature.txt +++ b/Documentation/config/feature.txt @@ -15,14 +15,6 @@ feature.experimental:: * `fetch.negotiationAlgorithm=skipping` may improve fetch negotiation times by skipping more commits at a time, reducing the number of round trips. + -* `fetch.writeCommitGraph=true` writes a commit-graph after every `git fetch` -command that downloads a pack-file from a remote. Using the `--split` option, -most executions will create a very small commit-graph file on top of the -existing commit-graph file(s). Occasionally, these files will merge and the -write may take longer. Having an updated commit-graph file helps performance -of many Git commands, including `git merge-base`, `git push -f`, and -`git log --graph`. -+ * `protocol.version=2` speeds up fetches from repositories with many refs by allowing the client to specify which refs to list before the server lists them. diff --git a/Documentation/config/fetch.txt b/Documentation/config/fetch.txt index b1a9b1461d3..b20394038d1 100644 --- a/Documentation/config/fetch.txt +++ b/Documentation/config/fetch.txt @@ -90,5 +90,4 @@ fetch.writeCommitGraph:: the existing commit-graph file(s). Occasionally, these files will merge and the write may take longer. Having an updated commit-graph file helps performance of many Git commands, including `git merge-base`, - `git push -f`, and `git log --graph`. Defaults to false, unless - `feature.experimental` is true. + `git push -f`, and `git log --graph`. Defaults to false. diff --git a/repo-settings.c b/repo-settings.c index dc6817daa95..0918408b344 100644 --- a/repo-settings.c +++ b/repo-settings.c @@ -51,14 +51,14 @@ void prepare_repo_settings(struct repository *r) UPDATE_DEFAULT_BOOL(r->settings.index_version, 4); UPDATE_DEFAULT_BOOL(r->settings.core_untracked_cache, UNTRACKED_CACHE_WRITE); } + if (!repo_config_get_bool(r, "fetch.writecommitgraph", &value)) r->settings.fetch_write_commit_graph = value; - if (!repo_config_get_bool(r, "feature.experimental", &value) && value) { - UPDATE_DEFAULT_BOOL(r->settings.fetch_negotiation_algorithm, FETCH_NEGOTIATION_SKIPPING); - UPDATE_DEFAULT_BOOL(r->settings.fetch_write_commit_graph, 1); - } UPDATE_DEFAULT_BOOL(r->settings.fetch_write_commit_graph, 0); + if (!repo_config_get_bool(r, "feature.experimental", &value) && value) + UPDATE_DEFAULT_BOOL(r->settings.fetch_negotiation_algorithm, FETCH_NEGOTIATION_SKIPPING); + /* Hack for test programs like test-dump-untracked-cache */ if (ignore_untracked_cache_config) r->settings.core_untracked_cache = UNTRACKED_CACHE_KEEP; -- 2.27.0.383.g050319c2ae
