async db access between requests on GAE/Python
You cannot start an async API call in one request and get its result in another.  The HTTP serving infrastructure will wait for all API calls started in a request to complete before the HTTP response is sent back; the data structure representing the async API call will be useless in the second request (even if it hits the same instance).
You might try Appstats to figure out what API calls your request is making and see if you can avoid some, use memcache for some, or parallellize.
You  might also use NDB which integrates memcache in the datastore API.
I'm trying to optimize my GAE webapp for latency.
The app has two requests which usually come one after another.
Is it safe to start an async db/memcache request during the first request and then use its results inside the following request?
(I'm aware that the second request might hit another instance. It would be handled as a cache miss)