1. A computer program product comprising a non-transitory computer readable storage medium having a computer readable program stored therein, wherein the computer readable program, when executed on a computing device, causes the computing device to: use a model to represent a system of annotators of a Question and Answer (QA) system pipeline, wherein the model represents each annotator in the system of annotators as a node having one or more performance parameters for indicating a performance of an execution of an annotator corresponding to the node, wherein each annotator in the system of annotators is a program that takes a portion of unstructured input text, extracts structured information from the portion of the unstructured input text, and generates annotations or metadata that are attached by the annotator to a source of the unstructured input text, wherein, for each node in the model, the one or more performance parameters corresponding to the node comprise an arrival rate parameter and a service rate parameter of the annotator associated with the node, wherein the arrival rate parameter indicates a number of jobs arriving in the node per second, and wherein the service rate parameter indicates a number of jobs being serviced by the node per second; determine, for each annotator in a set of annotators of the system of annotators, an effective response time for the annotator based on the one or more performance parameters; calculate a pre-execution start interval for a first annotator based on an effective response time of a second annotator, wherein execution of the first annotator is sequentially after execution of the second annotator; and schedule execution of pre-execution operations associated with the first annotator based on the calculated pre-execution start interval for the first annotator.