ETags，IIS7，内核缓存策略（enableKernelCache） [英] ETags, IIS7, Kernel Cache Policy (enableKernelCache)

问题描述

两部分问题（部分密切相关）：使用IIS7采用的默认OOTB ETag策略，为什么我们在浏览页面时看不到If-None-Match / 304交互？

Two-part question (parts are closely related): with the default OOTB ETag policy that IIS7 employs, why don't we see the If-None-Match/304 interaction as we navigate through pages?

例如，为空缓存请求返回的标头是：

The headers returned for an empty-cache request, for instance, are:

Content-Type    image/png
Last-Modified   Thu, 03 Dec 2009 15:51:56 GMT
Accept-Ranges   bytes
Etag    "a8a0628a3074ca1:0"
Server  Microsoft-IIS/7.0
X-Powered-By    ASP.NET
Date    Tue, 22 Dec 2009 19:47:36 GMT
Content-Length  1780

...然后对页面的后续访问不会为图像生成304往返？

...and yet subsequent accesses to the page don't generate a 304 round-trip for the image?

此外，IIS7的默认 applicationHost 文件具有以下（1）：

Also, the default applicationHost file for IIS7 has the following (1):

   <caching enabled="true" enableKernelCache="true">
   </caching>

enableKernelCache ='true'是否扩展到所有静态文件，释放你需要明确注册扩展名以授予 CacheUntilChange 作为内核策略（2）：

Does enableKernelCache='true' extend to all static files, freeing you of the need to register extensions explicitly to grant CacheUntilChange as the kernel policy (2):

<caching>
  <profiles>
    <add extension=".gif" policy="DontCache" kernelCachePolicy="CacheUntilChange" duration="0.00:01:00" location="Any" />
    <add extension=".png" policy="DontCache" kernelCachePolicy="CacheUntilChange" duration="0.00:01:00" location="Any" />
    <add extension=".js" policy="DontCache" kernelCachePolicy="CacheUntilChange" duration="0.00:01:00" location="Any" />
    <add extension=".css" policy="DontCache" kernelCachePolicy="CacheUntilChange" duration="0.00:01:00" location="Any" />
    <add extension=".jpg" policy="DontCache" kernelCachePolicy="CacheUntilChange" duration="0.00:01:00" location="Any" />
    <add extension=".jpeg" policy="DontCache" kernelCachePolicy="CacheUntilChange" duration="0.00:01:00" location="Any" />
  </profiles>
</caching>

（1）％systemroot％\ System32 \inetsrv \ config \ applicationHost.config

(1) %systemroot%\System32\inetsrv\config\applicationHost.config

（2） http://labs.episerver.com/en/Blogs/Per/Archive/2009/3/Configuring-cache-expiration-on-IIS-7/

推荐答案

ETag的处理和相关的If-None-Match / If-Modified-Since在某种程度上取决于浏览器。您可以尝试使用几种不同的浏览器，看看会发生什么 - 一般情况下，如果您没有设置明确的到期时间，我会期望看到304，就像您说的那样。

The handling of ETags and the associated If-None-Match / If-Modified-Since is somewhat browser dependent. You might try a few different browsers and see what happens -- in general, if you don't set an explicit expiration time, I would expect to see the 304's, as you said.

对于内核缓存，默认情况下会启用静态文件。为了帮助看看发生了什么，我发现运行以下命令很有帮助：

For kernel caching, it is enabled for static files by default. To help see what's happening, I've found it helpful to run the following command:

netsh http show cachestate

这将显示有关当前缓存中的文件的信息。

That will show information about the files that are currently in the cache.

请记住，在内核缓存文件之前，通常必须在特定时间窗口内多次引用文件。

Keep in mind that files normally have to be referenced a couple of times within a certain time window before the kernel will cache them.

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