Object caching

Cache functionality, including remote synchronization, is part of the EPiServer framework available for all EPiServer products. To allow cache management to be effectively shared between for instance CMS and Commerce. There are two interfaces, IObjectInstanceCache and ISynchronizedObjectInstanceCache, that can be used to access this functionality. Changes made using the ISynchronizedObjectInstanceCache interface are synchronized between servers using events in load balanced environments.

CacheEvictionPolicy

The CacheDependency class is tightly coupled to the HttpRuntime implementation and if you want to have a custom cache implementation you cannot rely on CacheDependency. For the object caching support in EPiServer framework you have the CacheEvictionPolicy class instead. It is very similar to CacheDependency but is completely de-coupled from any specific cache implementation.

Example on how to use CacheEvictionPolicy

public void AddToCache(string key, object val)
{
    // If you don't care about specific cache management, use CacheEvictionPolicy.Empty
    _cache.Insert(key, val, CacheEvictionPolicy.Empty);

    // To enable sliding expiration for 10s, depending on "otherKey"
    _cache.Insert(key, val, new CacheEvictionPolicy(
        new string[] { "otherKey" }, // Cache key dependency
        new TimeSpan(0, 0, 10),      // Always a timespan for timeouts
        CacheTimeoutType.Sliding);
}

Master keys

There is frequently a need to define a common dependency for cached data, frequently referred to as a master dependency or master key. To simplify the management of master keys this has been rolled into CacheEvictionPolicy – by including a list of key names these will automatically be added to the cache (if they do not exist) as regular cache entries. This means that you don't need to add code to conditionally add these entries before inserting your specific data into the cache.

In the example below the difference between the cache key dependency and the master key dependency is that if “otherKey” is not present in the cache then the data will never be inserted. If en entry with key “MasterKey” does not exist, then a dummy value will be added with the given key, thus allowing the data to be inserted successfully.

public void AddToCacheWithMasterDependency(string key, object val)
{
    // To enable absolute expiration for 5 minutes, depending on "otherKey" and master key dependency to "MasterKey"
    _cache.Insert(key, val, new CacheEvictionPolicy(
        null,                         // No file dependencies
        new string[] { "otherKey" },  // Cache key dependency
        new string[] { "MasterKey" }, // Master key dependency
        new TimeSpan(0, 5, 0),        // Always a timespan for timeouts
        CacheTimeoutType.Absolute);
}

Configuring caching of files

For the EPiServer platform, it is possible to configure which cache information is added to the response headers at request of static files. This can be used so files can be cached by the client and not served by the web server at each request meaning the total request time for a client can be reduced significantly.

The setting in web.config that controls the cache header directives “Expires” and “Cache-Control” is the configuration section staticFile that is allowed to be set on location level. This means it is possible to set different expiration times depending on the path to the static file. The staticFile configuration is used by both the StaticFileHandler that delivers files from Virtual Path Providers and by the media system in CMS.

Example:

<configuration>

<!--Configures expiration for files in CMS/VPP-->
<staticFile expirationTime="12:0:0" />

<!--Configures expiration in IIS-->
<system.webServer>
   <!--Configures client headers for static files from IIS-->
   <staticContent>
       <clientCache cacheControlMode="UseMaxAge" cacheControlMaxAge="1.00:00:00"></clientCache>
   </staticContent>
   <!--Configures output and kernel caching for ALL images (both CMS and IIS)-->
   <caching>
      <profiles>
        <add extension=".gif" policy="CacheUntilChange" kernelCachePolicy="CacheUntilChange" duration="0.00:01:00" location="Any" />
        <add extension=".png" policy="CacheUntilChange" kernelCachePolicy="CacheUntilChange" duration="0.00:01:00" location="Any" />
        <add extension=".js" policy="CacheUntilChange" kernelCachePolicy="CacheUntilChange" duration="0.00:01:00" location="Any" />
        <add extension=".css" policy="CacheUntilChange" kernelCachePolicy="CacheUntilChange" duration="0.00:01:00" location="Any" />
        <add extension=".jpg" policy="CacheUntilChange" kernelCachePolicy="CacheUntilChange" duration="0.00:01:00" location="Any" />
        <add extension=".jpeg" policy="CacheUntilChange" kernelCachePolicy="CacheUntilChange" duration="0.00:01:00" location="Any" />
      </profiles>
   </caching>
</system.webServer>
</configuration>