Question

Appengine docs mention a 1Mb limit on both entity size and batch get requests (db.get()):
http://code.google.com/appengine/docs/python/datastore/overview.html

Is there also a limit on the total size of all entities returned by a query for a single fetch() call?

Example query:

db.Model.all().fetch(1000)

Update: As of 1.4.0 batch get limits have been removed!

• Size and quantity limits on datastore batch get/put/delete operations have
  been removed. Individual entities are still limited to 1 MB, but your app
  may
  batch as many entities together for get/put/delete calls as the overall
  datastore deadline will allow for.

Answer 1

Theres no longer a limit on the number of entities that can be returned by a query, but the same entity size limit applies when you are actually retrieving / iterating over the entities. This will only be on a single entity at a time though; it is not a limit on the total size of all entities returned by the query.

Bottom line: as long as you don’t have a single entity that is > 1Mb you should be OK with queries.