libgit2 / libgit2/libgit2sharp

RewriteHistory extremely slow

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主要语言
C#
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描述

Reproduction steps

Find a repo with 3000+ commits
Run the below code against that repo to rewrite the repo history:

private static void RewriteHistory(string repoPath, ICollection<string> subFolders)
{
    using (var repo = new Repository(repoPath))
    {
        var refs = repo.Refs.Where(r => r.CanonicalName.EndsWith("develop")).OrderBy(r => r.CanonicalName).ToList();
        var commits = repo.Commits.QueryBy(new CommitFilter { IncludeReachableFrom = refs }).ToArray();
        var count = 0;
        var stopwatch = Stopwatch.StartNew();

        Logger.InfoFormat("Found {0} commits", commits.Length);
        Logger.InfoFormat("Rewrite history started");

        repo.Refs.RewriteHistory(new RewriteHistoryOptions
        {
            OnError = OnError,
            OnSucceeding = OnSucceeding,
            PruneEmptyCommits = true,
            CommitTreeRewriter = commit =>
            {
                Logger.InfoFormat("Commit {0}/{1}", ++count, commits.Length);

                var tree = TreeDefinition.From(commit);
                foreach (var treeEntry in commit.Tree)
                {
                    var match = subFolders.FirstOrDefault(s => treeEntry.Path.StartsWithIgnoreCase(s));

                    if (match == null)
                        tree.Remove(treeEntry.Path);
                }

                return tree;
            }
        }, commits);
        Logger.InfoFormat("Rewrite history ended. Took {0}", stopwatch.Elapsed);

        repo.Reset(ResetMode.Hard, repo.Head.Commits.First());
    }
}
Expected behavior

This should take a reasonable time. I expect it to take a few minutes for sure but not hours. For example when running something similar in git from the command like it takes minutes. I'm sorry I don't have specific times but I can try to provide more data to compare performance if necessary.

Actual behavior

This takes 1h 43 minutes of which 1h 40 to just start the rewrite and about a couple of minutes to go through all the commits.
INFO : Found 3486 commits
INFO : Rewrite history started
[between these two log messages there is a 1h 40m gap]
INFO : Commit 1/3486
INFO : Commit 2/3486
...
INFO : Rewrite history ended. Took 01:43:51.5536779

Version of LibGit2Sharp (release number or SHA1)

0.26.0 + 2.0.267 (native)

Operating system(s) tested; .NET runtime tested

.net 4.6.1 - Win 2012R2

贡献指南

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  2. 在 Issue 下留言说明你要接手 —— 这能避免两个人做同样的事。
  3. Fork 仓库,在一个分支上完成修改。
  4. 提交 Pull Request,并在描述里引用这个 Issue 编号。

调研方向

首先,使用包含 3,000 多个提交的 repository 重现该报告,并测量“Rewrite history started”与第一个 CommitTreeRewriter callback 之间的延迟。检查 issue 中显示的 RewriteHistory 调用及其 CommitTreeRewriter 设置。当相同的历史重写在几分钟而不是几小时内完成,同时保留报告中的 pruning 行为时,即表示完成。

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评估

技术栈
csharp, git
领域
devtools, performance
Issue 类型
缺陷
难度
4/5
预计耗时
3-5 天
活跃度
停滞
描述清晰度
基本清楚
新手友好度
35/100

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