Menu
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?
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
...and yet subsequent accesses to the page don't generate a 304 round-trip for the image?
Also, the default applicationHost file for IIS7 has the following (1):
<caching enabled="true" enableKernelCache="true">
</caching>
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
(2) http://labs.episerver.com/en/Blogs/Per/Archive/2009/3/Configuring-cache-expiration-on-IIS-7/
978
Caching Images in IISSelect a folder in the left pane or a single file in the right pane and open the Properties dialog. Check "Enable content expiration" and choose when your content should expire. That's it! IIS tells the client with the " Cache-Control " header that the content may be cached on the client.
Cache Kernel caches OS system objects such as threads, address spaces, and application kernels. The higher level application kernels provide the management functions for the application, managing thread priority and address spaces and reducing supervisor-level complexity.
If you want to disable caching of all files in a folder and its subfolders you can add a Web. config in the root folder you want to disable browser caching for. Say you wanted to disable browser caching for the files in the folder js/nocache and all subfolders, then you would place the Web. config here: js/nocache/Web.
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.
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
That will show information about the files that are currently in the cache.
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.
56
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With
