Memcached is one of the most common In-Memory cache implementation.  It was originally developed by Danga Interactive for LiveJournal, but is now used by many other sites as a side cache to speed up read mostly operations. It gained popularity in the non-Java world, too, especially since it’s a language-neutral side cache for which few alternatives existed.  

As a side-cache, Memcache clients relies on the database as the system of record, The database is still used for write,update and complex query operations.  Since the  memcached specification includes no query operations, memcached is not a database alternative, unlike most of the NoSQL offerings. It also exclude memcache from being a real solution for write scalability. As a result of that many of the heavy sites started to move away from Memcache and replace it with other NoSQL alternatives as noted in a recent highscalability post MySQL And Memcached: End Of An Era?

The transition away from memcached to NoSQL could represent a large investment as many sites are already heavily invested in memcached usage. In this post, I'll illustrate an alternative approach in which we’ll extend the use of memcache for write scaling, add other goodies such as high availability and elasticity by plugging GigaSpaces as the backend datastore, and avoid the need for a re-write. The pure Java implementation could also be seen as a benefit as it can increase the adoption of memcached within the Java community and leverage the portability of java to other platforms. more...