The invention introduces a non-transitory computer program product for scheduling execution of host commands when executed by a processing unit of a flash controller. Space of a random access memory of the flash controller is allocated for a first queue and a second queue, and the first queue stores the host commands issued by a host side in an order of time when the host commands arrive to the flash controller. The non-transitory computer program product includes program code to: migrate one or more host write commands from the top of the first queue to the second queue in an order of time when the host write commands arrive to the flash controller until the top of the first queue stores a host read command; fetch the host read command from the top of the first queue; execute the host read command to read user data from a flash module; and reply to the host side with the user data.