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ASP.NET Cache Limitations:

ASP.NET Cache provides a within a category of application so that you can cache frequently used data in an application data base and reduce costly trips. However, the ASP.NET cache is an in-process and stand-alone cache and therefore has many limitations and problems.

Restrictions deploying ASP.NET Cache:

Since the ASP.NET cache is always in progress, creates many limitations and problems. None of these problems occur when using the ASP.NET application NCache. Here is a list of problems and limitations.

Web Data Integrity Problem: Web garden is configured Web server by specifying multiple worker processes in application pool. However, in this case, ASP.NET will create a number of specific examples of the Cache class, one for each worker process. And the cache of each work process is not synchronized with other employees in the process of creating a problem of data integrity.

Loss of data with the recycling process work: The ASP.NET worker processes are carried out each of these employees and recycling processes by default. When the process recycles, the cache memory all is lost, because it was in the process. This can lead to serious problems if you do not have a backup archive of data stored in the cache. At a minimum, is a performance problem, because it is now necessary to download the entire cache.

Limit the cache size in-process cache to limit the amount of an individual process can be saved. Most ASP.NET applications these days, running 32-bit platforms, so it is 2GB or 3GB of memory size limit, which is a distributed cache and the ASP.NET application. While the 64-bit, this limit goes away, the recycling process will become even more serious performance problem, because the cache is now much larger and more performance to be recharged.

Single point of failure: the entire cache is stored on a single server, and thus will be lost if the server fails for any reason.

Problem of data integrity in the Web farm: A web farm is composed of multiple Web servers connected together via a load balancer. Load balance user requests directions to all Web servers and thus distribute the load evenly. In a configuration of Web farm, each Web server creates its own copy cache isolated from ASP.NET, which is not synchronized with other Web servers. This creates problems of data integrity.

Scalable Web Farm Problem: The ideal way to distribute the load evenly is a Web farm load balancing will send each request to the web server is appropriate for the load of all web servers. Since the ASP.NET cache is a stand-alone and in the process, load balancing, sends the request to the same web server where the user is initially maintained. This will significantly limit the scalability, because you may end up in situations where some servers are overloaded and very slow, while others are free, and with the addition of servers does not increase the total throughput processing.

Limitations SqlCacheDependency ASP.NET Cache

ASP.NET lets you use the SqlCacheDependency class to create a cache item dependent on a table or a row in a database. When there is a change in this table or a feature specific to the cache that this dependency has invalidated and removed from the cache. With SQL Server 2000, you can create a dependency at the tables, but SQL Server 2005, you can create a certain level of dependency.

Although SqlCacheDependency trying to deal with serious scalability limitations of ASP.NET Cache above, will not be able to completely solve the problems. Here are the problems SqlCacheDependency:

Performance Problem: The idea of ​​caching is to reduce expensive database trips. However, SqlCacheDependency stored in a database, and thus cause a significant degradation in performance. Whenever an ASP.NET adds, updates, or to remove any cache, the same information will be updated once the application database and the database SqlCacheDependency seconds. And ‘the database column, then all other cases, the garden of the Web cache or a web farm configuration. This makes the cache to be updated very slowly.

Scalability question database server is not able to mount with increasing farm. You may be able to build an active-active cluster of database, but until you can not grow beyond 2-3 server database without providing a significant performance degradation. In addition, this configuration is extremely costly. So if your farm grows, if you use SqlCacheDependency will see a significant decrease in performance.