1. A computer program product for processing a stream of tuples, the computer program product comprising a computer readable storage medium having program code embodied therewith, the program code comprising computer readable program code configured to: receive a stream of tuples to be processed by a plurality of processing elements operating on one or more computer processors; generate a model of performance for processing the stream of tuples at runtime, wherein one or more tuples from the stream of tuples potentially cause adverse performance; predict a parameter for a tuple from the stream of tuples, the parameter indicating a potential for adverse performance, the predicting including using the model; and modify processing of the tuple if the parameter falls outside a threshold.