The purgeServerSideCache method is deprecated and calling it has no effect - you'll get a console warning about that. This method is now replaced with refreshServerSideStore
Varnish is a state-of-the-art, high-performance HTTP accelerator. It uses the advanced features in Linux 2.6, FreeBSD 6/7 and Solaris 10 to achieve its high performance.
Overview Java Memcached is a high-performance, distributed memory object caching system, generic in nature, but intended for use in speeding up dynamic web applications by alleviating database load.