1. A method for tracing dataflow in a distributed computing application, comprising: incrementally advancing a dataflow in a dataflow path of one or more dataflow paths according to two or more directives encoded in two or more data messages, the dataflow path comprising one or more operators comprising at least one merge operator operative to: (i) combine the two or more data messages; and (ii) combine the two or more directives; and performing the two or more directives; wherein one or more of the incrementally advancing of the dataflow and the performing of the two or more directives are implemented as instruction code performed on a processor device.