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