Technology is described for debugging in a multi-processor environment. An example system can include a plurality of process icons representing processes executing on compute nodes. A plurality of relationship arc icons between the process icons can represent messages being sent between source processes and destination processes on the compute nodes. A tabular display control can have rows to display attributes for relationship arc icons representing the messages being sent. In addition, a grouping module can be used to identify groups of messages that are related and to highlight relationship arc icons which are part of a group.