A system selects multiple operators in a query graph by determining whether a corresponding value satisfies a threshold for each operator. The system sorts each selected operator in an ascending order based on a corresponding maximum thread capacity and determines an average number of threads of control based on available threads and the selected operators. The system allocates an initial number of threads to an initial selected operator in the ascending order, the initial number based on a minimum of the average number of threads and corresponding maximum thread capacity. The system determines a revised average number of threads based on remaining number of available threads and remaining number of the selected operators and allocates a next number of threads to a next selected operator in the ascending order, the next number based on a minimum of the revised average number of threads and corresponding maximum thread capacity.