1. A computer-implemented method comprising: as implemented by one or more computing devices configured with specific executable instructions, receiving a request to execute a first program code on a virtual compute system, the request including a first identifier identifying the first program code requested to be executed on the virtual compute system, wherein the virtual compute system comprises at least a first fleet of virtual machine instances configured to process low volume requests and a second fleet of virtual machine instances configured to process high volume requests; accessing, based on the first identifier included in the request, first program code data associated with the first program code from an electronic data store, wherein the first program code data indicates first execution frequency of the first program code, wherein the electronic data store is configured to store at least program code data associated with a plurality of program codes, the program code data indicating frequency of execution of the plurality of program codes on the virtual compute system; and based on the first execution frequency indicated by the first program code data, routing the request to the first fleet of virtual machine instances configured to process low volume requests.