java git gc似乎覆盖了一个packfile，留下了一个打开的文件描述符，其中包含对“oldxxx.pack”的引用

Question

在调试生产问题期间，我正在处理一个应用程序（Gerrit），该应用程序在缓存结构中保存对RandomAccessFile的引用

这些文件引用的是git存储库包文件

在存储库上的带外git gc（不在应用程序内）未发生更改的过程中，似乎：

1. 重写相同的包文件（相同的uuid）
2. 文件描述符以（old xxx.pack）的形式出现在lsof的输出列表中，但立即被标记（删除）

我已经为这个重命名搜索了很多代码库，但都没有结果

我的问题是，如果git gc对具有打开的文件描述符的文件进行重命名/覆盖，这会是一个文件系统的怪癖吗

入境限制：

java    25700 user  246r      REG                8,3      5090   1855936 ~/gerrit/git/RepoF.git/objects/pack/old-f4b8054434be1a227bdf8b12729efc1719f39708.pack (deleted)

git gc期间的inotify事件：

~/gerrit/git/RepoF.git/objects/pack/ OPEN,ISDIR 
~/gerrit/git/RepoF.git/objects/pack/ CLOSE_NOWRITE,CLOSE,ISDIR 
~/gerrit/git/RepoF.git/objects/pack/ OPEN pack-f4b8054434be1a227bdf8b12729efc1719f39708.idx
~/gerrit/git/RepoF.git/objects/pack/ OPEN pack-f4b8054434be1a227bdf8b12729efc1719f39708.pack
~/gerrit/git/RepoF.git/objects/pack/ ACCESS pack-f4b8054434be1a227bdf8b12729efc1719f39708.pack
~/gerrit/git/RepoF.git/objects/pack/ CLOSE_NOWRITE,CLOSE pack-f4b8054434be1a227bdf8b12729efc1719f39708.pack
~/gerrit/git/RepoF.git/objects/pack/ CLOSE_NOWRITE,CLOSE pack-f4b8054434be1a227bdf8b12729efc1719f39708.idx
~/gerrit/git/RepoF.git/objects/pack/ OPEN,ISDIR 
~/gerrit/git/RepoF.git/objects/pack/ CLOSE_NOWRITE,CLOSE,ISDIR 
~/gerrit/git/RepoF.git/objects/pack/ OPEN,ISDIR 
~/gerrit/git/RepoF.git/objects/pack/ CLOSE_NOWRITE,CLOSE,ISDIR 
~/gerrit/git/RepoF.git/objects/pack/ OPEN,ISDIR 
~/gerrit/git/RepoF.git/objects/pack/ CLOSE_NOWRITE,CLOSE,ISDIR 
~/gerrit/git/RepoF.git/objects/pack/ OPEN pack-f4b8054434be1a227bdf8b12729efc1719f39708.idx
~/gerrit/git/RepoF.git/objects/pack/ OPEN pack-f4b8054434be1a227bdf8b12729efc1719f39708.pack
~/gerrit/git/RepoF.git/objects/pack/ ACCESS pack-f4b8054434be1a227bdf8b12729efc1719f39708.pack
~/gerrit/git/RepoF.git/objects/pack/ CREATE tmp_pack_rG4dBh
~/gerrit/git/RepoF.git/objects/pack/ OPEN tmp_pack_rG4dBh
~/gerrit/git/RepoF.git/objects/pack/ MODIFY tmp_pack_rG4dBh
~/gerrit/git/RepoF.git/objects/pack/ CLOSE_WRITE,CLOSE tmp_pack_rG4dBh
~/gerrit/git/RepoF.git/objects/pack/ CREATE tmp_idx_NfF4Jh
~/gerrit/git/RepoF.git/objects/pack/ OPEN tmp_idx_NfF4Jh
~/gerrit/git/RepoF.git/objects/pack/ MODIFY tmp_idx_NfF4Jh
~/gerrit/git/RepoF.git/objects/pack/ CLOSE_WRITE,CLOSE tmp_idx_NfF4Jh
~/gerrit/git/RepoF.git/objects/pack/ MOVED_FROM tmp_pack_rG4dBh
~/gerrit/git/RepoF.git/objects/pack/ MOVED_TO .tmp-27710-pack-f4b8054434be1a227bdf8b12729efc1719f39708.pack
~/gerrit/git/RepoF.git/objects/pack/ MOVED_FROM tmp_idx_NfF4Jh
~/gerrit/git/RepoF.git/objects/pack/ MOVED_TO .tmp-27710-pack-f4b8054434be1a227bdf8b12729efc1719f39708.idx
~/gerrit/git/RepoF.git/objects/pack/ CLOSE_NOWRITE,CLOSE pack-f4b8054434be1a227bdf8b12729efc1719f39708.pack
~/gerrit/git/RepoF.git/objects/pack/ CLOSE_NOWRITE,CLOSE pack-f4b8054434be1a227bdf8b12729efc1719f39708.idx
~/gerrit/git/RepoF.git/objects/pack/ MOVED_FROM pack-f4b8054434be1a227bdf8b12729efc1719f39708.pack
---> ~/gerrit/git/RepoF.git/objects/pack/ MOVED_TO old-f4b8054434be1a227bdf8b12729efc1719f39708.pack   <----
~/gerrit/git/RepoF.git/objects/pack/ MOVED_FROM pack-f4b8054434be1a227bdf8b12729efc1719f39708.idx
~/gerrit/git/RepoF.git/objects/pack/ MOVED_TO old-f4b8054434be1a227bdf8b12729efc1719f39708.idx
~/gerrit/git/RepoF.git/objects/pack/ ATTRIB .tmp-27710-pack-f4b8054434be1a227bdf8b12729efc1719f39708.pack
~/gerrit/git/RepoF.git/objects/pack/ MOVED_FROM .tmp-27710-pack-f4b8054434be1a227bdf8b12729efc1719f39708.pack
~/gerrit/git/RepoF.git/objects/pack/ MOVED_TO pack-f4b8054434be1a227bdf8b12729efc1719f39708.pack
~/gerrit/git/RepoF.git/objects/pack/ ATTRIB .tmp-27710-pack-f4b8054434be1a227bdf8b12729efc1719f39708.idx
~/gerrit/git/RepoF.git/objects/pack/ MOVED_FROM .tmp-27710-pack-f4b8054434be1a227bdf8b12729efc1719f39708.idx
~/gerrit/git/RepoF.git/objects/pack/ MOVED_TO pack-f4b8054434be1a227bdf8b12729efc1719f39708.idx
---> ~/gerrit/git/RepoF.git/objects/pack/ DELETE old-f4b8054434be1a227bdf8b12729efc1719f39708.pack  <----
~/gerrit/git/RepoF.git/objects/pack/ DELETE old-f4b8054434be1a227bdf8b12729efc1719f39708.idx
~/gerrit/git/RepoF.git/objects/pack/ OPEN,ISDIR 
~/gerrit/git/RepoF.git/objects/pack/ CLOSE_NOWRITE,CLOSE,ISDIR 
~/gerrit/git/RepoF.git/objects/pack/ OPEN pack-f4b8054434be1a227bdf8b12729efc1719f39708.idx
~/gerrit/git/RepoF.git/objects/pack/ OPEN pack-f4b8054434be1a227bdf8b12729efc1719f39708.pack
~/gerrit/git/RepoF.git/objects/pack/ ACCESS pack-f4b8054434be1a227bdf8b12729efc1719f39708.pack
~/gerrit/git/RepoF.git/objects/pack/ OPEN,ISDIR 
~/gerrit/git/RepoF.git/objects/pack/ CLOSE_NOWRITE,CLOSE,ISDIR 
~/gerrit/git/RepoF.git/objects/pack/ CLOSE_NOWRITE,CLOSE pack-f4b8054434be1a227bdf8b12729efc1719f39708.pack
~/gerrit/git/RepoF.git/objects/pack/ CLOSE_NOWRITE,CLOSE pack-f4b8054434be1a227bdf8b12729efc1719f39708.idx
~/gerrit/git/RepoF.git/objects/pack/ OPEN,ISDIR 
~/gerrit/git/RepoF.git/objects/pack/ CLOSE_NOWRITE,CLOSE,ISDIR 
~/gerrit/git/RepoF.git/objects/pack/ OPEN pack-f4b8054434be1a227bdf8b12729efc1719f39708.idx
~/gerrit/git/RepoF.git/objects/pack/ OPEN pack-f4b8054434be1a227bdf8b12729efc1719f39708.pack
~/gerrit/git/RepoF.git/objects/pack/ ACCESS pack-f4b8054434be1a227bdf8b12729efc1719f39708.pack
~/gerrit/git/RepoF.git/objects/pack/ OPEN,ISDIR 
~/gerrit/git/RepoF.git/objects/pack/ CLOSE_NOWRITE,CLOSE,ISDIR 
~/gerrit/git/RepoF.git/objects/pack/ CLOSE_NOWRITE,CLOSE pack-f4b8054434be1a227bdf8b12729efc1719f39708.pack
~/gerrit/git/RepoF.git/objects/pack/ CLOSE_NOWRITE,CLOSE pack-f4b8054434be1a227bdf8b12729efc1719f39708.idx
~/gerrit/git/RepoF.git/objects/pack/ OPEN,ISDIR 
~/gerrit/git/RepoF.git/objects/pack/ CLOSE_NOWRITE,CLOSE,ISDIR 

Answer 1

如果在存储库中执行标准git gc而不做任何更改，则这是意料之中的。Git根据其内容的散列来命名其打包文件。因为Git不会为现有包重新计算增量，当您git gc并且只有一个包而没有松散对象时，它很可能会将所有数据打包到一个与旧包相同的包中

发生这种情况时，Git仍然会打开旧包的文件描述符，因为它不会立即关闭包。这是因为经常需要再次访问它们，所以它会尝试让它们打开一段时间。仍处于打开状态的旧包将重命名为旧名称，新包将重命名到位；然后删除旧包。在Unix系统上，完全可以删除打开了文件描述符的文件；当最后一个进程关闭其文件描述符时，存储被释放

因此，对于您描述的场景来说，这一切似乎完全正常。通常git gc不是no op，因为会向包中添加或删除其他对象，或者将多个包合并为一个包。但是，如果您在运行一个git gc之后立即运行一个git gc，而没有中间更改，那么这是意料之中的