The move puts App Engine on a more equal footing with Microsoft's Windows Azure and Amazon Web Services, which launched its ElastiCache service in August 2011. Platform-as-a-service (PaaS) offerings Heroku and Engine Yard also offer caching services.
The App Engine service is based on open source Memcached (pronounced "mem-cache d"), a caching system that automatically saves frequently used data to cache and, when necessary, pushes out aging data as it falls into disuse. It was created by Brad Fitzpatrick in 2003 to support the operation of the interactive consumer site LiveJournal. It was later rewritten in C and became a popular open source code module.
Caching systems are frequently used with transaction processing and high-activity Web applications. They store data as objects in server memory or add on solid state modules, retrieving data at high rates of speed without going to a disk-based data store. Facebook, Zynga, You Tube, Twitter and Reddit are all examples of applications that rely on Memcached.
[ Want to learn more about Amazon's ElastiCache? See Amazon Goes After Cloud App Speed Bumps. ]
Google App Engine's caching service is available through its API and is still in preview form. It nevertheless allows a developer using App Engine to designate an amount of cache to be used with his, and only his, application, rather than relying on the platform's shared caching service. Google announced the addition of the service to App Engine release 1.8.2 in a blog post Wednesday.
Google will charge 12 cents per GB for up to 20 GBs of dedicated cache. The alternative, shared Memcache service is free. The Google pricing appears to be higher than Amazon's ElastiCache pricing, although an exact comparison is difficult because of what might be varying amounts of CPU power provided with the caching service. Amazon lists the amount of CPU assigned to the cache node; Google didn't in its "preview" announcement.
Amazon ElastiCache's on-demand, standard extra-large cache node is priced at 62 cents for 14.6 GBs of memory, or 4.25 cents per GB. Google's charge would be $1.80 for a slightly larger 15 GB cache node at 12 cents a GB.
The Google blog said users could move between the shared cache service and dedicated cache without changing their applications.