为什么文件属性中的“访问时间”和“修改时间”不一致？

深碍√TFBOYSˉ_ 2022-06-13 12:18 414阅读 0赞

转载地址：http://greenerycn.cnblogs.com/

在Win7下，我注意到一个现象，就是经常文件属性中的“访问时间”和“修改时间”是不一致的，如下图：

[![image][]][image 1]

这个文件是我在21:41 创建的，然后我在21:42修理里面的内容并保存。按照常理，访问时间应该和修改时间一致才对。现象是反而比修改时间早，很奇怪。

根据[GetFileTime][]这个API，和文件相关的时间有3个：

BOOL WINAPI GetFileTime(
      __in       HANDLE hFile,
      __out_opt  LPFILETIME lpCreationTime,
      __out_opt  LPFILETIME lpLastAccessTime,
      __out_opt  LPFILETIME lpLastWriteTime
    );

CreationTime:创建时间，很好理解，就是这个文件创建时的时间。

LastAccessTime:最后访问时间，表示文件读取，写入，复制或者执行的最后时间.

LastWriteTime:  文件最后写入的时间。

从这个定义来看的话，LastAccessTime应该大于等于LastWriteTime.但是从使用来看的话，却又不是这样的。

### Why? ###

今天看了[The Old New Thing][]才明白过来，原来从2003 SP1起，为了性能，默认把LastAccessTime给禁用了。

我使用的是Win7系统，默认是关闭的。

### 那么它为什么会影响性能呢？ ###

LastAccessTime会保存到两个地方：

*  文件属性中，作为MFT中的一条记录
 *  该文件所属的目录索引中。

影响性能的主要原因是如果一个文件只是读操作的话，为了更新这个时间，就必须做一个写操作，把该信息写入到文件属性和目录索引中去，这样一个读操作就变成了一个读+写操作。由于现在的硬盘都非常大，几十万个文件都是常事，如果读操作再加一个写操作，那么这个确实影响性能。（详细可以参考Fsutil: behavior 中对于DisableLastAccess的描述，地址附后）。

下面是各个文件系统对文件时间的支持文档：

<table style="margin:0px; padding:0px; border:1px solid silver; border-collapse:collapse; word-break:break-word; color:rgb(51,51,51); font-family:arial,nsimsun,sans-serif; font-size:14px; width:443pt"> 
 <tbody style="margin:0px; padding:0px"> 
 <tr style="margin:0px; padding:0px; height:14.25pt"> 
 <td style="margin:0px; padding:3px; border:1pt solid rgb(187,187,187); border-collapse:collapse; background-color:rgb(229,229,229); width:214pt; height:14.25pt"> Feature</td> 
 <td style="margin:0px; padding:3px; border-width:1pt 1pt 1pt 1px; border-style:solid; border-color:rgb(187,187,187); border-collapse:collapse; background-color:rgb(229,229,229); width:40pt"> NTFS</td> 
 <td style="margin:0px; padding:3px; border-width:1pt 1pt 1pt 1px; border-style:solid; border-color:rgb(187,187,187); border-collapse:collapse; background-color:rgb(229,229,229); width:49pt"> exFAT</td> 
 <td style="margin:0px; padding:3px; border-width:1pt 1pt 1pt 1px; border-style:solid; border-color:rgb(187,187,187); border-collapse:collapse; background-color:rgb(229,229,229); width:49pt"> UDF</td> 
 <td style="margin:0px; padding:3px; border-width:1pt 1pt 1pt 1px; border-style:solid; border-color:rgb(187,187,187); border-collapse:collapse; background-color:rgb(229,229,229); width:91pt"> FAT32</td> 
 </tr> 
 <tr style="margin:0px; padding:0px; height:24.75pt"> 
 <td style="margin:0px; padding:3px; border-width:1px 1pt 1pt; border-style:solid; border-color:rgb(187,187,187); border-collapse:collapse; width:214pt; height:24.75pt"> Creation time stamps（创建时间）</td> 
 <td style="margin:0px; padding:3px; border-width:1px 1pt 1pt 1px; border-style:solid; border-color:rgb(187,187,187); border-collapse:collapse; width:40pt"> Yes</td> 
 <td style="margin:0px; padding:3px; border-width:1px 1pt 1pt 1px; border-style:solid; border-color:rgb(187,187,187); border-collapse:collapse; width:49pt"> Yes</td> 
 <td style="margin:0px; padding:3px; border-width:1px 1pt 1pt 1px; border-style:solid; border-color:rgb(187,187,187); border-collapse:collapse; width:49pt"> Yes</td> 
 <td style="margin:0px; padding:3px; border-width:1px 1pt 1pt 1px; border-style:solid; border-color:rgb(187,187,187); border-collapse:collapse; width:91pt"> Yes</td> 
 </tr> 
 <tr style="margin:0px; padding:0px; height:24.75pt"> 
 <td style="margin:0px; padding:3px; border-width:1px 1pt 1pt; border-style:solid; border-color:rgb(187,187,187); border-collapse:collapse; width:214pt; height:24.75pt"> Last access time stamps(最后访问时间)</td> 
 <td style="margin:0px; padding:3px; border-width:1px 1pt 1pt 1px; border-style:solid; border-color:rgb(187,187,187); border-collapse:collapse; width:40pt"> No*</td> 
 <td style="margin:0px; padding:3px; border-width:1px 1pt 1pt 1px; border-style:solid; border-color:rgb(187,187,187); border-collapse:collapse; width:49pt"> Yes</td> 
 <td style="margin:0px; padding:3px; border-width:1px 1pt 1pt 1px; border-style:solid; border-color:rgb(187,187,187); border-collapse:collapse; width:49pt"> Yes</td> 
 <td style="margin:0px; padding:3px; border-width:1px 1pt 1pt 1px; border-style:solid; border-color:rgb(187,187,187); border-collapse:collapse; width:91pt"> Yes (只更新日期)</td> 
 </tr> 
 <tr style="margin:0px; padding:0px; height:24.75pt"> 
 <td style="margin:0px; padding:3px; border-width:1px 1pt 1pt; border-style:solid; border-color:rgb(187,187,187); border-collapse:collapse; width:214pt; height:24.75pt"> Last change time stamps(最后改变时间)</td> 
 <td style="margin:0px; padding:3px; border-width:1px 1pt 1pt 1px; border-style:solid; border-color:rgb(187,187,187); border-collapse:collapse; width:40pt"> Yes</td> 
 <td style="margin:0px; padding:3px; border-width:1px 1pt 1pt 1px; border-style:solid; border-color:rgb(187,187,187); border-collapse:collapse; width:49pt"> Yes</td> 
 <td style="margin:0px; padding:3px; border-width:1px 1pt 1pt 1px; border-style:solid; border-color:rgb(187,187,187); border-collapse:collapse; width:49pt"> Yes</td> 
 <td style="margin:0px; padding:3px; border-width:1px 1pt 1pt 1px; border-style:solid; border-color:rgb(187,187,187); border-collapse:collapse; width:91pt"> Yes</td> 
 </tr> 
 <tr style="margin:0px; padding:0px; height:24.75pt"> 
 <td style="margin:0px; padding:3px; border-width:1px 1pt 1pt; border-style:solid; border-color:rgb(187,187,187); border-collapse:collapse; width:214pt; height:24.75pt"> Last archive time stamps(最后存档时间)</td> 
 <td style="margin:0px; padding:3px; border-width:1px 1pt 1pt 1px; border-style:solid; border-color:rgb(187,187,187); border-collapse:collapse; width:40pt"> No</td> 
 <td style="margin:0px; padding:3px; border-width:1px 1pt 1pt 1px; border-style:solid; border-color:rgb(187,187,187); border-collapse:collapse; width:49pt"> No</td> 
 <td style="margin:0px; padding:3px; border-width:1px 1pt 1pt 1px; border-style:solid; border-color:rgb(187,187,187); border-collapse:collapse; width:49pt"> No</td> 
 <td style="margin:0px; padding:3px; border-width:1px 1pt 1pt 1px; border-style:solid; border-color:rgb(187,187,187); border-collapse:collapse; width:91pt"> No</td> 
 </tr> 
 </tbody> 
</table>

说明：

1.NTFS 本身是支持更新LastAccessTime,在Windows 2000,XP,2003中默认是开启的，Vista之后需要单独开启。

### 如何开启LastAccessTime的更新呢？ ###

使用命令查询当前系统是否关闭了LastAccessTime的更新：

fsutil behavior query disablelastaccess

[![image][image 2]][image_image 2]

1 表示关闭，0表示开启

关闭LastAccessTime的更新：

fsutil behavior set disablelastaccess 1

[![image][image 3]][image_image 3]

注意：需要重启。

打开LastAccessTime的更新：

fsutil behavior set disablelastaccess 0

[![image][image 4]][image_image 4]

注意：需要重启。

事实上，上面的修改都是修改的注册表

Key: \[HKEY\_LOCAL\_MACHINE\\SYSTEM\\CurrentControlSet\\Control\\FileSystem\]   
Value Name: NtfsDisableLastAccessUpdate   
Data Type: REG\_DWORD (DWORD Value)   
Value Data: (0 = disable, 1 = enable)

[![image][image 5]][image_image 5]

### 参考资料 ###

FILE\_BASIC\_INFO Structure

[http://msdn.microsoft.com/zh-cn/library/aa364217(VS.85).aspx][http_msdn.microsoft.com_zh-cn_library_aa364217_VS.85_.aspx]

SetFileTime Function

[http://msdn.microsoft.com/en-us/library/ms724933(VS.85).aspx][http_msdn.microsoft.com_en-us_library_ms724933_VS.85_.aspx]

GetFileTime Function

[http://msdn.microsoft.com/en-us/library/ms724320(v=VS.85).aspx][GetFileTime]

File System Functionality Comparison

[http://msdn.microsoft.com/en-us/library/ee681827(VS.85).aspx][http_msdn.microsoft.com_en-us_library_ee681827_VS.85_.aspx]

What's the difference between LastWriteTime and ChangeTime in FILE\_BASIC\_INFO?

[http://blogs.msdn.com/b/oldnewthing/archive/2010/07/09/10036162.aspx][The Old New Thing]

Disabling Last Access Time in Windows Vista to improve NTFS performance

[http://blogs.technet.com/b/filecab/archive/2006/11/07/disabling-last-access-time-in-windows-vista-to-improve-ntfs-performance.aspx][http_blogs.technet.com_b_filecab_archive_2006_11_07_disabling-last-access-time-in-windows-vista-to-improve-ntfs-performance.aspx]

Enable Last Access Time Stamp To Files In Windows 7 \[How-To\]

[http://www.groovypost.com/howto/microsoft/enable-last-access-time-stamp-to-files-folder-windows-7/][http_www.groovypost.com_howto_microsoft_enable-last-access-time-stamp-to-files-folder-windows-7]

KB894372:Support for Windows Server 2003 SP1 on Windows Storage Server 2003-based server appliances

[http://support.microsoft.com/?scid=kb;en-us;894372&x=9&y=15][http_support.microsoft.com_scid_kb_en-us_894372_x_9_y_15]

NtfsDisableLastAccessUpdate

[http://technet.microsoft.com/en-us/library/cc758569(WS.10).aspx][http_technet.microsoft.com_en-us_library_cc758569_WS.10_.aspx]

Fsutil: behavior

[http://www.microsoft.com/resources/documentation/windows/xp/all/proddocs/en-us/fsutil\_behavior.mspx?mfr=true][http_www.microsoft.com_resources_documentation_windows_xp_all_proddocs_en-us_fsutil_behavior.mspx_mfr_true]

[image]: /images/20220613/f1d4fb66c49a4e0580a69d7c127a2bd7.png
[image 1]: http://images.cnblogs.com/cnblogs_com/greenerycn/WindowsLiveWriter/a961f47e35f7_132E3/image_2.png
[GetFileTime]: http://msdn.microsoft.com/en-us/library/ms724320%28v=VS.85%29.aspx
[The Old New Thing]: http://blogs.msdn.com/b/oldnewthing/archive/2010/07/09/10036162.aspx
[image 2]: http://images.cnblogs.com/cnblogs_com/greenerycn/WindowsLiveWriter/a961f47e35f7_132E3/image_thumb_1.png
[image_image 2]: /images/20220613/47a33a8615a34b00aef63c3bef11051d.png
[image 3]: http://images.cnblogs.com/cnblogs_com/greenerycn/WindowsLiveWriter/a961f47e35f7_132E3/image_thumb_2.png
[image_image 3]: /images/20220613/4e43e7a0b3354128884d53fc0d05367b.png
[image 4]: http://images.cnblogs.com/cnblogs_com/greenerycn/WindowsLiveWriter/a961f47e35f7_132E3/image_thumb_3.png
[image_image 4]: /images/20220613/97e1924d693146ccb8ca6b6af92b3714.png
[image 5]: http://images.cnblogs.com/cnblogs_com/greenerycn/WindowsLiveWriter/a961f47e35f7_132E3/image_thumb_4.png
[image_image 5]: /images/20220613/40f3ff572c2f4b83b2700b7ca1318ea9.png
[http_msdn.microsoft.com_zh-cn_library_aa364217_VS.85_.aspx]: http://msdn.microsoft.com/zh-cn/library/aa364217%28VS.85%29.aspx
[http_msdn.microsoft.com_en-us_library_ms724933_VS.85_.aspx]: http://msdn.microsoft.com/en-us/library/ms724933%28VS.85%29.aspx
[http_msdn.microsoft.com_en-us_library_ee681827_VS.85_.aspx]: http://msdn.microsoft.com/en-us/library/ee681827%28VS.85%29.aspx
[http_blogs.technet.com_b_filecab_archive_2006_11_07_disabling-last-access-time-in-windows-vista-to-improve-ntfs-performance.aspx]: http://blogs.technet.com/b/filecab/archive/2006/11/07/disabling-last-access-time-in-windows-vista-to-improve-ntfs-performance.aspx
[http_www.groovypost.com_howto_microsoft_enable-last-access-time-stamp-to-files-folder-windows-7]: http://www.groovypost.com/howto/microsoft/enable-last-access-time-stamp-to-files-folder-windows-7/
[http_support.microsoft.com_scid_kb_en-us_894372_x_9_y_15]: http://support.microsoft.com/?scid=kb;en-us;894372&x=9&y=15
[http_technet.microsoft.com_en-us_library_cc758569_WS.10_.aspx]: http://technet.microsoft.com/en-us/library/cc758569%28WS.10%29.aspx
[http_www.microsoft.com_resources_documentation_windows_xp_all_proddocs_en-us_fsutil_behavior.mspx_mfr_true]: http://www.microsoft.com/resources/documentation/windows/xp/all/proddocs/en-us/fsutil_behavior.mspx?mfr=true