Distributed Caching On The Path To Scalability

By Iqbal Khan

If you're developing an ASP.NET application, Web services or a high-performance computing (HPC) application, you're likely to encounter major scalability issues as you try to scale and put more load on your application. With an ASP.NET application, bottlenecks occur in two data stores. The first is the application data that resides in the database, and the other is ASP.NET session state data that is typically stored in one of three modes (InProc, StateServer, or SqlServer) provided by Microsoft. All three have major scalability issues.

Web services typically do not use session state, but they do have scalability bottlenecks when it comes to application data. Just like ASP.NET applications, Web services can be hosted in IIS and deployed in a Web farm for scalability.

HPC applications that are designed to perform massive parallel processing also have scalability problems because the data store does not scale in the same manner. HPC (also called grid computing) has traditionally used Java, but as .NET gains market share, it is becoming more popular for HPC applications as well. HPC applications are deployed to hundreds and sometimes thousands of computers for parallel processing, and they often need to operate on large amounts of data and share intermediate results with other computers. HPC applications use a database or a shared file system as a data store, and both of these do not scale very well.

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Distributed Caching

Caching is a well-known concept in both the hardware and software worlds. Traditionally, caching has been a stand-alone mechanism, but that is not workable anymore in most environments because applications now run on multiple servers and in multiple processes within each server.

In-memory distributed caching is a form of caching that allows the cache to span multiple servers so that it can grow in size and in transactional capacity. Distributed caching has become feasible now for a number of reasons. First, memory has become very cheap, and you can stuff computers with many gigabytes at throwaway prices. Second, network cards have become very fast, with 1Gbit now standard everywhere and 10Gbit gaining traction. Finally, unlike a database server, which usually requires a high-end machine, distributed caching works well on lower cost machines (like those used for Web servers), which allows you to add more machines easily.

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