Checking Content Freshness

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Checking Content Freshness

Typically, when a client requests content, the cache proxy plug-in first checks the expiration date. If the cached content has expired, the plug-in calls either CompareContentInformation on the IWMSCacheProxyServer interface or GetContentInformation on the IWMSCacheProxyServer interface. The cache server responds by contacting the origin server and requesting a content information context that can be used to determine whether the cached content remains up to date. This process is called a Get Content Information (GCI) request.

If a GCI request passes through an upstream cache proxy server before getting to the origin server, it is possible that the cache proxy server will fulfill the request from cache rather than passing it on.

The expiration date is determined by a content administrator. If the administrator does not identify a date, the content can be cached indefinitely and it is not necessary to perform a freshness check. For more information, see Persisting Cached Content. Alternatively, if content is set to expire immediately, the cache plug-in must always request a freshness check.

  • Note   Windows Media Services version 4.1 does not support expiration dates or freshness checking. Therefore, a server running Windows Media Services 9 Series sets the expiration time to one hour when obtaining content from a server running Windows Media Services version 4.1.

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