1. A computer program product for processing a stream of tuples, the computer program product comprising a non-transitory computer readable storage device 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, each processing element having one or more stream operators, wherein an operator graph defines how tuples are routed to processing elements for processing, the operator graph including a source operator to output the stream of tuples to the plurality of processing elements, each processing element receiving tuples from and outputting tuples into the stream of tuples; identify a processing location within the one or more stream operators, the processing location including a first stream operator, wherein a second stream operator receives tuples from the first stream operator; determine an output pattern at the second stream operator and identify a grouping location within the one or more stream operators based on the output pattern, the determining an output pattern includes determining that the second stream operator outputs a first quantity of one or more tuples for every second quantity of one or more tuples that the second stream operator receives, the first and second quantity of one or more tuples being included in the stream of tuples, the grouping location including the second stream operator, wherein the second stream operator is capable of receiving tuples according to a runtime grouping condition; and modify processing at the first stream operator within the processing location based on the second stream operator outputting the first quantity and receiving the second quantity, the modifying including adding the runtime grouping condition to the first stream operator, the runtime grouping condition to cause the first stream operator to group a third quantity of one or more tuples to send to the second stream operator, wherein the third quantity of one or more tuples matches the second quantity of one or more tuples that the second stream operator receives.