much like tracing the difference is that the inserted code increments a pre defined accumulator or accumulates elapsed time into such an accumulator each time an event occurs rather than recording the event itself data collection and reduction program 21 receives the produced data 12 and will reduce the data before any logging takes place program 21 groups the reduced data into three groups and logs different details for each group the first group is global data logged in global data file 23 the second group is process data logged in process data file 24 the third group is workload data logged in workload data file 25 global data in global data file 23 consists of global data records of standard metrics which report system performance on computing system 11 as a whole records are added to this file for example at the rate of one every five minutes process data in process data file 24 consists of process data records of standard metrics which contains information on any process which is found to be 34 interesting 34 during a specified interval specified interval is for example one minute records are typically added to process data file 24 at the end of each specified interval a process is found to be 34 interesting 34 when it meets any one or more of the following criteria a process is seen for the first time i e it is started a process uses more of a given resource than a user defined.