René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"git_revwalk_next is slow on first iteration since v0.25","articleBody":"git_revwalk_next is slow on its first iteration for versions 0.25, 0.26 and master when compared to v0.24. This is especially noticeable on large repositories.\r\n\r\n### Reproduction steps\r\nRun the following program on the Linux kernel source tree (https://github.com/torvalds/linux):\r\n\r\n```c\r\n#include \u003cstdio.h\u003e\r\n#include \u003cgit2.h\u003e\r\n\r\nint main(int argc, char *argv[]) {\r\n        git_libgit2_init();\r\n\r\n        git_repository *repo;\r\n        if (git_repository_open(\u0026repo, \".git\")) {\r\n                fprintf(stderr, \"Failed to open repository\\n\");\r\n                return 1;\r\n        }\r\n\r\n        git_oid oid;\r\n        git_oid_fromstr(\u0026oid, \"a0651c7fa2c088a605f63792279859608ed7f2c8\");\r\n\r\n        git_revwalk *revwalk;\r\n        git_revwalk_new(\u0026revwalk, repo);\r\n        git_revwalk_sorting(revwalk, GIT_SORT_TIME);\r\n        git_revwalk_push(revwalk, \u0026oid);\r\n\r\n        if (!git_revwalk_next(\u0026oid, revwalk)) {\r\n                git_commit *commit;\r\n\r\n                if (git_commit_lookup(\u0026commit, repo, \u0026oid)) {\r\n                        fprintf(stderr, \"Failed to lookup commit\\n\");\r\n                        return 1;\r\n                }\r\n\r\n                printf(\"%s\\n\", git_commit_message(commit));\r\n                git_commit_free(commit);\r\n        }\r\n\r\n        git_revwalk_free(revwalk);\r\n        git_repository_free(repo);\r\n\r\n        return 0;\r\n}\r\n```\r\n\r\n### Expected behavior\r\nWhen using v0.24 this program runs in a couple of milliseconds:\r\n```\r\nrichard@DevNew:~/code/linux$ time ./revwalktest \u003e/dev/null\r\n\r\nreal\t0m0.006s\r\nuser\t0m0.000s\r\nsys\t0m0.006s\r\n```\r\n\r\n### Actual behavior\r\nWhen using v0.25, v0.26 or master this program has not completed after 1 minute:\r\n```\r\nrichard@DevNew:~/code/linux$ timeout 60s ./revwalktest\r\nrichard@DevNew:~/code/linux$ echo $?\r\n124\r\n```\r\n\r\n### Version of libgit2 (release number or SHA1)\r\nv0.25, v0.26 \u0026 master\r\n\r\n### Operating system(s) tested\r\n```\r\nLinux DevNew 4.13.0-17-generic #20-Ubuntu SMP Mon Nov 6 10:04:08 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux\r\n```","author":{"url":"https://github.com/rgburke","@type":"Person","name":"rgburke"},"datePublished":"2017-12-01T21:24:00.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":30},"url":"https://github.com/4428/libgit2/issues/4428"}