Question

Does anyone have an idea how the use of multiple ORs impacts performance in app engine (cpu time use maybe?). Something like:

select from users where username = 'bob' or
    username = 'jane' or
    username = 'greg' or
    username = 'Nth user';

I think we can only layer 30 of these in at once. I’m curious if this operation would be done in parallel (all the ors go out at once) or each is done serially.

Thanks

Answer 1

You can do:

SELECT FROM users WHERE username IN ('bob', 'jane', 'greg', 'Nth user')

For cleanliness. Here’s what Google says about its impact on performance:

Note: The IN and != operators use
multiple queries behind the scenes.
For example, the IN operator executes
a separate underlying datastore query
for every item in the list. The
entities returned are a result of the
cross-product of all the underlying
datastore queries and are
de-duplicated. A maximum of 30
datastore queries are allowed for any
single GQL query.

http://code.google.com/appengine/docs/python/datastore/gqlreference.html