A system and method for performing distributed execution of database queries includes a query server that receives a query to be executed on a database, forms a query plan based on the query, assigns tasks to task slots on a plurality of worker nodes in a cluster, and, upon receipt of a notification that a task has completed on a worker node, immediately assigns an unassigned task to a free task slot on that worker node, such that the task may begin executing on that worker node substantially immediately thereafter. The task slots on worker nodes include pools of resources that run tasks without start-up overhead.