Does anyone know what haystack backends work on appengine with the cloudsql db?
I had a similar problem and did not find any GAE friendly way to use Django Haystack. You may be able to do something with Whoosh as it is pure Python, but I have my doubts.
An alternative is the use of Django nonrel search. It does not contain all the features of Haystack and its associated backends, but it may provide what you need.