Seamless memcache caching of all entities

This is a class that seamlessly caches entities. Everything happens transparently.

All you need to do is:

import datastore_cache datastore_cache.DatastoreCachingShim.Install()

Details

Then use the datastore as you would without using memcache. All entities will be cached in memcache as they pass through this api proxy. Your get requests will be served out of memcache if there is a hit. The cache is updated through:

• puts
• gets
• queries

Limitations:

The cache is completely pessimistic in the case of transactions. In case of a request that is part of a transaction:

• gets are not served from the cache
• puts/deletes invalidate those entities from the cache when they commit
• puts/deletes do not change the cache if they rollback

If your entity keys are larger than the size allowed for memcache keys the cache will fail

Thanks to Nick Johnson for the original idea to do this at the api proxy stub level and the original sketch of the code.