1. A data processing system for generating trace data, the data processing system comprising: determining means, responsive to detecting a trace event, for determining whether at least one identifier for the detected trace event matches a recorded at least one identifier in a record of a set of previously recorded trace events; first placing means, responsive to determining that the at least one identifier for the detected trace event does not match a recorded at least one identifier in a record of the set of previously recorded trace events, for placing complete trace information for the detected trace event in the record; and second placing means, responsive to determining that the at least one identifier for the detected trace event matches a recorded at least one identifier in a record of the set of previously recorded trace events, for placing partial trace information for the detected trace event in the record in the trace data.