1. A method for managing resource consumption in a computing system, the method comprising: predefining a resource policy by predefining a plurality of threshold values relating to the resource consumption, wherein the predefining includes predefining the plurality of threshold values and an action, wherein the resources are consumed by a plurality of user-defined functions performing tasks for a database management system, wherein the user-defined functions are fenced user-defined functions, wherein the user-defined function extends predefined functions of the database management system, wherein the user-defined functions are initiated by the database management system, wherein the resources comprises at least one of a number of database tables, a number of input operations per time unit, and a number of output operations per time unit, wherein the user-defined functions are executed by a plurality of processes external to the database management system; and performing the action, as defined by the resource policy, on at least one of the user-defined functions, wherein the action is first performed on one of a newest one of the at least one of the user-defined functions and an oldest one of the at least one of the user-defined functions, wherein the action is a queuing of a request for starting of a user-defined function additional to already executing user-defined functions when a first predefined threshold of the resource policy is exceeded, and wherein the action is a rejection of a request for starting of a user-defined function additional to already executing user-defined functions when a second predefined threshold of the resource policy is exceeded, wherein the action is a forced cancellation of a user-defined function when a third threshold of the resource policy is exceeded, wherein the first threshold is less than the second threshold and the second threshold is less than the third threshold, wherein the resource comprises an amount of main memory, wherein a calculation of the amount of main memory is based on an aggregated amount of memory of all executing user-defined functions, wherein the user-defined functions are registered as external processes to core database management system functions in a repository.