reuse-delta-base: improves some documentation The current code got me a bit confused initially. So a bit more documentation around it cannot hurt.

tests: expect the message from 1baf0fffd82f in test-hghave.t (issue6762) Couldn't reproduce locally, but apparently this message may occasionally pop up when running this test.

branching: merge stable into default

changelog-v2: add a configuration to disable rank computation We encountered a graph where rank computation was pathologically slow. We add an option to disable this computation while this is getting fixed. Disabling the rank computation should allow for testing other changelog-v2 features undisturbed (like changeset-based copy tracing). I am purposely not adding a test for the new non-default code path, as this is a temporary work around of an experimental feature.

debugrevlog: display total stored information This is an interesting statistis, so let's display it.

debug-revlog: details about non-ancestors delta-bases Deltas against a base that is not an ancestor of the revision that owns this delta are notable. For example, they introduce complexity during the bundling process as the base might not exist on the unbundling side. We detect them in `hg debugrevlog` and print information about them.

debug-revlog: move the code in revlogutils module We have a module dedicated to debug code, let us use it.

debug-revlog: move the --dump code in `revlogutils` module We have a module dedicated to debug code, let us use it.

delta-find: set the default candidate chunk size to 10 I ran performance and storage tests on repositories of various sizes and shapes for the following values of the config : 5, 10, 20, 50, 100, no-chunking The performance tests do not show any statistical impact on computation times for large pushes and pulls. For searching for an individual delta, this can provide a significant performance improvement with a minor degradation of space-quality on the result. (see data at the end of the commit). For overall store size, the change : - does not have any impact on many small repositories, - has an observable, but very negligible impact on most larger repositories. - One private repository we use for testing sees a small increase in size (1%) in the narrower version. We will try to get more numbers on a larger version of that repository to make sure nothing pathological happens. We pick "10" as the limit as "5" seems a bit more risky. There are room to improve the current code, by using more aggressive filtering and better (i.e any) sorting of the candidates. However this is already a large improvement for pathological cases, with little impact in the common situations. The initial motivation for this change is to fix performance of delta computation for a file where the previous code ended up testing 20 000 possible candidate-bases in one go, which is… slow. This affected about ½ of the file revisions leading to atrocious performance, especially during some push/pull operations. Details about individual delta finding timing: ---------------------------------------------- The vast majority of benchmark cases are unchanged but the three below. The first two do not see any impact on the final delta. The last one sees a change in delta-size that is negligible compared to the full text size. ### data-env-vars.name = mozilla-try-2019-02-18-zstd-sparse-revlog # benchmark.name = perf-delta-find # benchmark.variants.rev = manifest-snapshot-many-tries-a (revision 756096) ∞: 5.844783 5: 4.473523 (-23.46%) 10: 4.970053 (-14.97%) 20: 5.770386 (-1.27%) 50 5.821358 100: 5.834887 MANIFESTLOG: rev = 756096: (no-limit) delta-base = 301840 search-rounds = 6 try-count = 60 delta-type = snapshot snap-depth = 7 delta-size = 179 MANIFESTLOG: rev=756096: (limit = 10) delta-base=301840 search-rounds=9 try-count=51 delta-type=snapshot snap-depth=7 delta-size=179 ### data-env-vars.name = mozilla-try-2019-02-18-zstd-sparse-revlog # benchmark.name = perf-delta-find # benchmark.variants.rev = manifest-snapshot-many-tries-d (revision 754060) ∞: 5.017663 5: 3.655931 (-27.14%) 10: 4.095436 (-18.38%) 20: 4.828949 (-3.76%) 50 4.987574 100: 4.994889 MANIFESTLOG: rev=754060: (no limit) delta-base=301840 search-rounds=5 try-count=53 delta-type=snapshot snap-depth=7 delta-size = 179 MANIFESTLOG: rev=754060: (limite = 10) delta-base=301840 search-rounds=8 try-count=45 delta-type=snapshot snap-depth=7 delta-size = 179 ### data-env-vars.name = mozilla-try-2019-02-18-zstd-sparse-revlog # benchmark.name = perf-delta-find # bin-env-vars.hg.flavor = rust # benchmark.variants.rev = manifest-snapshot-many-tries-e (revision 693368) ∞: 4.869282 5: 2.039732 (-58.11%) 10: 2.413537 (-50.43%) 20: 4.449639 (-8.62%) 50 4.865863 100: 4.882649 MANIFESTLOG: rev=693368: delta-base=693336 search-rounds=6 try-count=53 delta-type=snapshot snap-depth=6 full-test-size=131065 delta-size=199 MANIFESTLOG: rev=693368: delta-base=278023 search-rounds=5 try-count=21 delta-type=snapshot snap-depth=4 full-test-size=131065 delta-size=278 Raw data for store size (in bytes) for various chunk size value below: ---------------------------------------------------------------------- 440 134 384 5 pypy/.hg/store/ 440 134 384 10 pypy/.hg/store/ 440 134 384 20 pypy/.hg/store/ 440 134 384 50 pypy/.hg/store/ 440 134 384 100 pypy/.hg/store/ 440 134 384 ... pypy/.hg/store/ 666 987 471 5 netbsd-xsrc-2022-11-15/.hg/store/ 666 987 471 10 netbsd-xsrc-2022-11-15/.hg/store/ 666 987 471 20 netbsd-xsrc-2022-11-15/.hg/store/ 666 987 471 50 netbsd-xsrc-2022-11-15/.hg/store/ 666 987 471 100 netbsd-xsrc-2022-11-15/.hg/store/ 666 987 471 ... netbsd-xsrc-2022-11-15/.hg/store/ 852 844 884 5 netbsd-pkgsrc-2022-11-15/.hg/store/ 852 844 884 10 netbsd-pkgsrc-2022-11-15/.hg/store/ 852 844 884 20 netbsd-pkgsrc-2022-11-15/.hg/store/ 852 844 884 50 netbsd-pkgsrc-2022-11-15/.hg/store/ 852 844 884 100 netbsd-pkgsrc-2022-11-15/.hg/store/ 852 844 884 ... netbsd-pkgsrc-2022-11-15/.hg/store/ 1 504 227 981 5 netbeans-2018-08-01-sparse-zstd/.hg/store/ 1 504 227 871 10 netbeans-2018-08-01-sparse-zstd/.hg/store/ 1 504 227 813 20 netbeans-2018-08-01-sparse-zstd/.hg/store/ 1 504 227 813 50 netbeans-2018-08-01-sparse-zstd/.hg/store/ 1 504 227 813 100 netbeans-2018-08-01-sparse-zstd/.hg/store/ 1 504 227 813 ... netbeans-2018-08-01-sparse-zstd/.hg/store/ 3 875 801 068 5 netbsd-src-2022-11-15/.hg/store/ 3 875 696 767 10 netbsd-src-2022-11-15/.hg/store/ 3 875 696 757 20 netbsd-src-2022-11-15/.hg/store/ 3 875 696 653 50 netbsd-src-2022-11-15/.hg/store/ 3 875 696 653 100 netbsd-src-2022-11-15/.hg/store/ 3 875 696 653 ... netbsd-src-2022-11-15/.hg/store/ 4 531 441 314 5 mozilla-central/.hg/store/ 4 531 435 157 10 mozilla-central/.hg/store/ 4 531 432 045 20 mozilla-central/.hg/store/ 4 531 429 119 50 mozilla-central/.hg/store/ 4 531 429 119 100 mozilla-central/.hg/store/ 4 531 429 119 ... mozilla-central/.hg/store/ 4 875 861 390 5 mozilla-unified/.hg/store/ 4 875 855 155 10 mozilla-unified/.hg/store/ 4 875 852 027 20 mozilla-unified/.hg/store/ 4 875 848 851 50 mozilla-unified/.hg/store/ 4 875 848 851 100 mozilla-unified/.hg/store/ 4 875 848 851 ... mozilla-unified/.hg/store/ 11 498 764 601 5 mozilla-try/.hg/store/ 11 497 968 858 10 mozilla-try/.hg/store/ 11 497 958 730 20 mozilla-try/.hg/store/ 11 497 927 156 50 mozilla-try/.hg/store/ 11 497 925 963 100 mozilla-try/.hg/store/ 11 497 923 428 ... mozilla-try/.hg/store/ 10 047 914 031 5 private-repo 9 969 132 101 10 private-repo 9 944 745 015 20 private-repo 9 939 756 703 50 private-repo 9 939 833 016 100 private-repo 9 939 822 035 ... private-repo

delta-find: add a way to control the number of bases tested at the same time See inline comment for details. The feature is currently disabled, but should be enabled by default to mitigate some existing pathological cases. Also see the next changeset for details.