Database query processing may be scaled using additional processing clusters. A database query is received at a processing cluster. A determination is made as to whether additional processing clusters will be used to process the database query. Operations to cause compute nodes of the processing cluster to instruct operations at the additional processing clusters are included in a plan generated to perform database queries determined to use additional processing clusters. The plan is executed to be perform the database query causing compute nodes of the processing cluster to send instructions to corresponding additional processing clusters in order to generate and return a response to the database query.