Currently, admission control queuing occurs synchronously w.r.t. the ExecuteStatement client RPC. That is, a query handle is not returned until the query is admitted.
Instead, the queuing should occur on the asynchronous path. That way, the client gets a query handle back immediately and can e.g. cancel a query that is in the admission control queue.
We'll also need a way to better expose the progress of a query handle (related to IMPALA-124). E.g. that the query is queued for admission and what resource(s) it's waiting on.