1. A method for monitoring transaction based systems monitoring their system resource and transaction performance data with thresholds on metrics, said method comprising the steps of collecting system resource data and transaction performance data on a period basis and each time a transaction performance metric is passed, triggering the collection of the system resource and storing an identifier correlating the transaction performance data and the system resource data; merging the collected system resource and transaction performance data; calculating the mean value for each system resource or transaction performance metric of merged data; identifying the metrics for which there is a significant difference between mean value obtained with triggering or without triggering; according to the identified metric mean value, calculating new thresholds of system resource metrics to be used for monitoring. The steps of the method are repeated as many times as necessary for a good training of the system monitoring. Alternatively, the method can be applied to a service offering distributed environment wherein the servers collect locally monitoring data, sending it for further processing on a manager server which sends back the new resource monitoring inputs.