1. A computer-implemented method executed by at least one processor for improving performance of an application at runtime, the method comprising the steps of: (A) displaying an operator graph that represents the application using a plurality of operators and a plurality of data flows between the plurality of operators; (B) analyzing the operator graph at runtime when the application runs; (C) detecting at least one problem in the operator graph based on at least one data bottleneck in the operator graph; and (D) performing at least one resource reallocation to improve performance of the application represented in the operator graph.