Merge branch 'jc/worktree-git-path'

2024-06-24T23:39:15Z

Code cleanup. * jc/worktree-git-path: worktree_git_path(): move the declaration to path.h

worktree_git_path(): move the declaration to path.h

2024-06-08T18:42:37Z

The definition of this function is in path.c but its declaration is in worktree.h, which is something unexpected. The function is explained as "Similar to git_path()"; declaring it next to where git_path() is declared would make more sense. Signed-off-by: Junio C Hamano

path: move `validate_headref()` to its only user

2024-05-07T05:50:48Z

While `validate_headref()` is only called from `is_git_directory()` in "setup.c", it is currently implemented in "path.c". Move it over such that it becomes clear that it is only really used during setup in order to discover repositories. Signed-off-by: Patrick Steinhardt Signed-off-by: Junio C Hamano

Merge branch 'rs/apply-lift-path-length-limit'

2024-04-15T21:11:42Z

"git apply" has been updated to lift the hardcoded pathname length limit, which in turn allowed a mksnpath() function that is no longer used. * rs/apply-lift-path-length-limit: path: remove mksnpath() apply: avoid fixed-size buffer in create_one_file()

path: remove mksnpath()

2024-04-05T16:49:38Z

Remove the function mksnpath(), which has become unused. Signed-off-by: René Scharfe Signed-off-by: Junio C Hamano

refs: introduce reftable backend

2024-02-07T16:28:37Z

Due to scalability issues, Shawn Pearce has originally proposed a new "reftable" format more than six years ago [1]. Initially, this new format was implemented in JGit with promising results. Around two years ago, we have then added the "reftable" library to the Git codebase via a4bbd13be3 (Merge branch 'hn/reftable', 2021-12-15). With this we have landed all the low-level code to read and write reftables. Notably missing though was the integration of this low-level code into the Git code base in the form of a new ref backend that ties all of this together. This gap is now finally closed by introducing a new "reftable" backend into the Git codebase. This new backend promises to bring some notable improvements to Git repositories: - It becomes possible to do truly atomic writes where either all refs are committed to disk or none are. This was not possible with the "files" backend because ref updates were split across multiple loose files. - The disk space required to store many refs is reduced, both compared to loose refs and packed-refs. This is enabled both by the reftable format being a binary format, which is more compact, and by prefix compression. - We can ignore filesystem-specific behaviour as ref names are not encoded via paths anymore. This means there is no need to handle case sensitivity on Windows systems or Unicode precomposition on macOS. - There is no need to rewrite the complete refdb anymore every time a ref is being deleted like it was the case for packed-refs. This means that ref deletions are now constant time instead of scaling linearly with the number of refs. - We can ignore file/directory conflicts so that it becomes possible to store both "refs/heads/foo" and "refs/heads/foo/bar". - Due to this property we can retain reflogs for deleted refs. We have previously been deleting reflogs together with their refs to avoid file/directory conflicts, which is not necessary anymore. - We can properly enumerate all refs. With the "files" backend it is not easily possible to distinguish between refs and non-refs because they may live side by side in the gitdir. Not all of these improvements are realized with the current "reftable" backend implementation. At this point, the new backend is supposed to be a drop-in replacement for the "files" backend that is used by basically all Git repositories nowadays. It strives for 1:1 compatibility, which means that a user can expect the same behaviour regardless of whether they use the "reftable" backend or the "files" backend for most of the part. Most notably, this means we artificially limit the capabilities of the "reftable" backend to match the limits of the "files" backend. It is not possible to create refs that would end up with file/directory conflicts, we do not retain reflogs, we perform stricter-than-necessary checks. This is done intentionally due to two main reasons: - It makes it significantly easier to land the "reftable" backend as tests behave the same. It would be tough to argue for each and every single test that doesn't pass with the "reftable" backend. - It ensures compatibility between repositories that use the "files" backend and repositories that use the "reftable" backend. Like this, hosters can migrate their repositories to use the "reftable" backend without causing issues for clients that use the "files" backend in their clones. It is expected that these artificial limitations may eventually go away in the long term. Performance-wise things very much depend on the actual workload. The following benchmarks compare the "files" and "reftable" backends in the current version: - Creating N refs in separate transactions shows that the "files" backend is ~50% faster. This is not surprising given that creating a ref only requires us to create a single loose ref. The "reftable" backend will also perform auto compaction on updates. In real-world workloads we would likely also want to perform pack loose refs, which would likely change the picture. Benchmark 1: update-ref: create refs sequentially (refformat = files, refcount = 1) Time (mean ± σ): 2.1 ms ± 0.3 ms [User: 0.6 ms, System: 1.7 ms] Range (min … max): 1.8 ms … 4.3 ms 133 runs Benchmark 2: update-ref: create refs sequentially (refformat = reftable, refcount = 1) Time (mean ± σ): 2.7 ms ± 0.1 ms [User: 0.6 ms, System: 2.2 ms] Range (min … max): 2.4 ms … 2.9 ms 132 runs Benchmark 3: update-ref: create refs sequentially (refformat = files, refcount = 1000) Time (mean ± σ): 1.975 s ± 0.006 s [User: 0.437 s, System: 1.535 s] Range (min … max): 1.969 s … 1.980 s 3 runs Benchmark 4: update-ref: create refs sequentially (refformat = reftable, refcount = 1000) Time (mean ± σ): 2.611 s ± 0.013 s [User: 0.782 s, System: 1.825 s] Range (min … max): 2.597 s … 2.622 s 3 runs Benchmark 5: update-ref: create refs sequentially (refformat = files, refcount = 100000) Time (mean ± σ): 198.442 s ± 0.241 s [User: 43.051 s, System: 155.250 s] Range (min … max): 198.189 s … 198.670 s 3 runs Benchmark 6: update-ref: create refs sequentially (refformat = reftable, refcount = 100000) Time (mean ± σ): 294.509 s ± 4.269 s [User: 104.046 s, System: 190.326 s] Range (min … max): 290.223 s … 298.761 s 3 runs - Creating N refs in a single transaction shows that the "files" backend is significantly slower once we start to write many refs. The "reftable" backend only needs to update two files, whereas the "files" backend needs to write one file per ref. Benchmark 1: update-ref: create many refs (refformat = files, refcount = 1) Time (mean ± σ): 1.9 ms ± 0.1 ms [User: 0.4 ms, System: 1.4 ms] Range (min … max): 1.8 ms … 2.6 ms 151 runs Benchmark 2: update-ref: create many refs (refformat = reftable, refcount = 1) Time (mean ± σ): 2.5 ms ± 0.1 ms [User: 0.7 ms, System: 1.7 ms] Range (min … max): 2.4 ms … 3.4 ms 148 runs Benchmark 3: update-ref: create many refs (refformat = files, refcount = 1000) Time (mean ± σ): 152.5 ms ± 5.2 ms [User: 19.1 ms, System: 133.1 ms] Range (min … max): 148.5 ms … 167.8 ms 15 runs Benchmark 4: update-ref: create many refs (refformat = reftable, refcount = 1000) Time (mean ± σ): 58.0 ms ± 2.5 ms [User: 28.4 ms, System: 29.4 ms] Range (min … max): 56.3 ms … 72.9 ms 40 runs Benchmark 5: update-ref: create many refs (refformat = files, refcount = 1000000) Time (mean ± σ): 152.752 s ± 0.710 s [User: 20.315 s, System: 131.310 s] Range (min … max): 152.165 s … 153.542 s 3 runs Benchmark 6: update-ref: create many refs (refformat = reftable, refcount = 1000000) Time (mean ± σ): 51.912 s ± 0.127 s [User: 26.483 s, System: 25.424 s] Range (min … max): 51.769 s … 52.012 s 3 runs - Deleting a ref in a fully-packed repository shows that the "files" backend scales with the number of refs. The "reftable" backend has constant-time deletions. Benchmark 1: update-ref: delete ref (refformat = files, refcount = 1) Time (mean ± σ): 1.7 ms ± 0.1 ms [User: 0.4 ms, System: 1.2 ms] Range (min … max): 1.6 ms … 2.1 ms 316 runs Benchmark 2: update-ref: delete ref (refformat = reftable, refcount = 1) Time (mean ± σ): 1.8 ms ± 0.1 ms [User: 0.4 ms, System: 1.3 ms] Range (min … max): 1.7 ms … 2.1 ms 294 runs Benchmark 3: update-ref: delete ref (refformat = files, refcount = 1000) Time (mean ± σ): 2.0 ms ± 0.1 ms [User: 0.5 ms, System: 1.4 ms] Range (min … max): 1.9 ms … 2.5 ms 287 runs Benchmark 4: update-ref: delete ref (refformat = reftable, refcount = 1000) Time (mean ± σ): 1.9 ms ± 0.1 ms [User: 0.5 ms, System: 1.3 ms] Range (min … max): 1.8 ms … 2.1 ms 217 runs Benchmark 5: update-ref: delete ref (refformat = files, refcount = 1000000) Time (mean ± σ): 229.8 ms ± 7.9 ms [User: 182.6 ms, System: 46.8 ms] Range (min … max): 224.6 ms … 245.2 ms 6 runs Benchmark 6: update-ref: delete ref (refformat = reftable, refcount = 1000000) Time (mean ± σ): 2.0 ms ± 0.0 ms [User: 0.6 ms, System: 1.3 ms] Range (min … max): 2.0 ms … 2.1 ms 3 runs - Listing all refs shows no significant advantage for either of the backends. The "files" backend is a bit faster, but not by a significant margin. When repositories are not packed the "reftable" backend outperforms the "files" backend because the "reftable" backend performs auto-compaction. Benchmark 1: show-ref: print all refs (refformat = files, refcount = 1, packed = true) Time (mean ± σ): 1.6 ms ± 0.1 ms [User: 0.4 ms, System: 1.1 ms] Range (min … max): 1.5 ms … 2.0 ms 1729 runs Benchmark 2: show-ref: print all refs (refformat = reftable, refcount = 1, packed = true) Time (mean ± σ): 1.6 ms ± 0.1 ms [User: 0.4 ms, System: 1.1 ms] Range (min … max): 1.5 ms … 1.8 ms 1816 runs Benchmark 3: show-ref: print all refs (refformat = files, refcount = 1000, packed = true) Time (mean ± σ): 4.3 ms ± 0.1 ms [User: 0.9 ms, System: 3.3 ms] Range (min … max): 4.1 ms … 4.6 ms 645 runs Benchmark 4: show-ref: print all refs (refformat = reftable, refcount = 1000, packed = true) Time (mean ± σ): 4.5 ms ± 0.2 ms [User: 1.0 ms, System: 3.3 ms] Range (min … max): 4.2 ms … 5.9 ms 643 runs Benchmark 5: show-ref: print all refs (refformat = files, refcount = 1000000, packed = true) Time (mean ± σ): 2.537 s ± 0.034 s [User: 0.488 s, System: 2.048 s] Range (min … max): 2.511 s … 2.627 s 10 runs Benchmark 6: show-ref: print all refs (refformat = reftable, refcount = 1000000, packed = true) Time (mean ± σ): 2.712 s ± 0.017 s [User: 0.653 s, System: 2.059 s] Range (min … max): 2.692 s … 2.752 s 10 runs Benchmark 7: show-ref: print all refs (refformat = files, refcount = 1, packed = false) Time (mean ± σ): 1.6 ms ± 0.1 ms [User: 0.4 ms, System: 1.1 ms] Range (min … max): 1.5 ms … 1.9 ms 1834 runs Benchmark 8: show-ref: print all refs (refformat = reftable, refcount = 1, packed = false) Time (mean ± σ): 1.6 ms ± 0.1 ms [User: 0.4 ms, System: 1.1 ms] Range (min … max): 1.4 ms … 2.0 ms 1840 runs Benchmark 9: show-ref: print all refs (refformat = files, refcount = 1000, packed = false) Time (mean ± σ): 13.8 ms ± 0.2 ms [User: 2.8 ms, System: 10.8 ms] Range (min … max): 13.3 ms … 14.5 ms 208 runs Benchmark 10: show-ref: print all refs (refformat = reftable, refcount = 1000, packed = false) Time (mean ± σ): 4.5 ms ± 0.2 ms [User: 1.2 ms, System: 3.3 ms] Range (min … max): 4.3 ms … 6.2 ms 624 runs Benchmark 11: show-ref: print all refs (refformat = files, refcount = 1000000, packed = false) Time (mean ± σ): 12.127 s ± 0.129 s [User: 2.675 s, System: 9.451 s] Range (min … max): 11.965 s … 12.370 s 10 runs Benchmark 12: show-ref: print all refs (refformat = reftable, refcount = 1000000, packed = false) Time (mean ± σ): 2.799 s ± 0.022 s [User: 0.735 s, System: 2.063 s] Range (min … max): 2.769 s … 2.836 s 10 runs - Printing a single ref shows no real difference between the "files" and "reftable" backends. Benchmark 1: show-ref: print single ref (refformat = files, refcount = 1) Time (mean ± σ): 1.5 ms ± 0.1 ms [User: 0.4 ms, System: 1.0 ms] Range (min … max): 1.4 ms … 1.8 ms 1779 runs Benchmark 2: show-ref: print single ref (refformat = reftable, refcount = 1) Time (mean ± σ): 1.6 ms ± 0.1 ms [User: 0.4 ms, System: 1.1 ms] Range (min … max): 1.4 ms … 2.5 ms 1753 runs Benchmark 3: show-ref: print single ref (refformat = files, refcount = 1000) Time (mean ± σ): 1.5 ms ± 0.1 ms [User: 0.3 ms, System: 1.1 ms] Range (min … max): 1.4 ms … 1.9 ms 1840 runs Benchmark 4: show-ref: print single ref (refformat = reftable, refcount = 1000) Time (mean ± σ): 1.6 ms ± 0.1 ms [User: 0.4 ms, System: 1.1 ms] Range (min … max): 1.5 ms … 2.0 ms 1831 runs Benchmark 5: show-ref: print single ref (refformat = files, refcount = 1000000) Time (mean ± σ): 1.6 ms ± 0.1 ms [User: 0.4 ms, System: 1.1 ms] Range (min … max): 1.5 ms … 2.1 ms 1848 runs Benchmark 6: show-ref: print single ref (refformat = reftable, refcount = 1000000) Time (mean ± σ): 1.6 ms ± 0.1 ms [User: 0.4 ms, System: 1.1 ms] Range (min … max): 1.5 ms … 2.1 ms 1762 runs So overall, performance depends on the usecases. Except for many sequential writes the "reftable" backend is roughly on par or significantly faster than the "files" backend though. Given that the "files" backend has received 18 years of optimizations by now this can be seen as a win. Furthermore, we can expect that the "reftable" backend will grow faster over time when attention turns more towards optimizations. The complete test suite passes, except for those tests explicitly marked to require the REFFILES prerequisite. Some tests in t0610 are marked as failing because they depend on still-in-flight bug fixes. Tests can be run with the new backend by setting the GIT_TEST_DEFAULT_REF_FORMAT environment variable to "reftable". There is a single known conceptual incompatibility with the dumb HTTP transport. As "info/refs" SHOULD NOT contain the HEAD reference, and because the "HEAD" file is not valid anymore, it is impossible for the remote client to figure out the default branch without changing the protocol. This shortcoming needs to be handled in a subsequent patch series. As the reftable library has already been introduced a while ago, this commit message will not go into the details of how exactly the on-disk format works. Please refer to our preexisting technical documentation at Documentation/technical/reftable for this. [1]: https://public-inbox.org/git/CAJo=hJtyof=HRy=2sLP0ng0uZ4=S-DpZ5dR1aF+VHVETKG20OQ@mail.gmail.com/ Original-idea-by: Shawn Pearce Based-on-patch-by: Han-Wen Nienhuys Signed-off-by: Patrick Steinhardt Signed-off-by: Junio C Hamano

refs: convert MERGE_AUTOSTASH to become a normal pseudo-ref

2024-01-19T19:10:41Z

Similar to the preceding conversion of the AUTO_MERGE pseudo-ref, let's convert the MERGE_AUTOSTASH ref to become a normal pseudo-ref as well. Signed-off-by: Patrick Steinhardt Signed-off-by: Junio C Hamano

refs: convert AUTO_MERGE to become a normal pseudo-ref

2024-01-19T19:10:41Z

In 70c70de616 (refs: complete list of special refs, 2023-12-14) we have inrtoduced a new `is_special_ref()` function that classifies some refs as being special. The rule is that special refs are exclusively read and written via the filesystem directly, whereas normal refs exclucsively go via the refs API. The intent of that commit was to record the status quo so that we know to route reads of such special refs consistently. Eventually, the list should be reduced to its bare minimum of refs which really are special, namely FETCH_HEAD and MERGE_HEAD. Follow up on this promise and convert the AUTO_MERGE ref to become a normal pseudo-ref by using the refs API to both read and write it instead of accessing the filesystem directly. Signed-off-by: Patrick Steinhardt Signed-off-by: Junio C Hamano

path: move related function to path

2023-06-12T20:49:36Z

Move path-related function from strbuf.[ch] to path.[ch] so that strbuf is focused on string manipulation routines with minimal dependencies. repository.h is no longer a necessary dependency after moving this function out. Signed-off-by: Calvin Wan Signed-off-by: Junio C Hamano

path.h: move function declarations for path.c functions from cache.h

2023-03-21T17:56:52Z

Signed-off-by: Elijah Newren Signed-off-by: Junio C Hamano

git/path.h, branch v2.46.2