Provided are methods, apparatus and computer programs for monitoring operational data relating to a sequence of data processing operations in a network of data processing units. In response to specified boundaries for data gathering, operational data is selectively gathered into discrete data partitions for a desired time period, a desired set of processing nodes, and/or a desired set of process executions. A set of event listeners invoke operations of a data gatherer in response to events within a processing sequence and the data gatherer allocates operational data to different ones of a set of discrete logical data containers in response to notifications from the event listeners. The data collection is responsive to system events such as a collection interval expiry to end data collection for a first partition and start data collection for a second partition.