  We present some measurements and ideas for response time statistics in ERP
systems. It is shown that the response time distribution of a given transaction
in a given system is generically a log-normal distribution or, in some
situations, a sum of two or more log-normal distributions. We present some
arguments for this form of the distribution based on heuristic rules for
response times, and we show data from performance measurements in actual
systems to support the log-normal form. Deviations of the log-normal form can
often be traced back to performance problems in the system. Consequences for
the interpretation of response time data and for service level agreements are
discussed.
