Sliding and Absolute expiration in Caching

Caching Mechanism and Its Expirations

ASP.net cache or AppFabric Caching are ways to increase the performance of the web application by reducing server round trips to database.


However the validity of the cached data needs to be ensured, to enforce this, we have the following options
1. Dependency Mechanisms:
     Files, SQL Cache Dependency etc
This ensures that the cache is re-validated or refreshed once a dependent has changed or been altered


2.  Expire Cache:
     The cache will expire after a time frame and the newer items will be added to cache when ever accessed or processed after expiry. 


In Cache Expiry, we have the following options

1. Absolute Expiration:  Absolute expiration means It will expire cache after some time period set at the time of activating cache. This will be absolute expiration whether cache will be used or not It will expire the cache. This type of expiration used to  cache data which are not frequently changing.

2. Sliding Expiration: Sliding expiration means It will expire cache after time period at the time of activating cache if any request is not made during this time period. This type of expiration is useful when there are so many data to cache. So It will put those items in the cache which are frequently used in the application. So it will not going to use unnecessary memory.

Example:

string cacheData = "The data to be cached";

//Absolute Expiration

Cache.Insert("AbsoluteCacheKey", cacheData, null,

 DateTime.Now.AddMinutes(1), System.Web.Caching.Cache.NoSlidingExpiration);

//Sliding Expiration

Cache.Insert("SlidingExpiration", cacheData, null,

System.Web.Caching.Cache.NoAbsoluteExpiration, TimeSpan.FromMinutes(1));

-- Saravanan