A system optimizes performance of parallel queries by dividing a query into a plurality of sub queries. The query is divided according to a plurality of data ranges associated with the query. The system creates an available queue, and a defer queue. The system assigns the plurality of sub queries into the available queue. The system then processes, in parallel, the plurality of sub queries in the available queue. During the processing, if the system determines that a data range associated with a sub query comprises unavailable data, the system assigns the sub query to the defer queue as a defer range sub query. After completing the processing of the plurality of sub queries in the available queue, the system processes a plurality of defer range sub queries in the defer queue.