Question

I seem to remember reading somewhere that google app engine automatically caches the results of very frequent queries into memory so that they are retrieved faster.

Is this correct?

If so, is there still a charge for datastore reads on these queries?

Answer 1

If you’re using Python and the new ndb API, it DOES have automatic caching of entities, so if you fetch entities by key, it would be cached:

http://code.google.com/appengine/docs/python/ndb/cache.html

As the comments say, queries are not cached.
Cached requests don’t hit the datastore, so you save on reads there.

If you’re using Java, or the other APIs for accessing the datastore, then no, there’s no caching.

edited Fixed my mistake about queries getting cached.