1. A computer-implemented method for classifying messages, comprising: monitoring a plurality of messages which are sent to an application, each message includes a request for the application to perform a transaction, and the application executes in response to the request of each message; obtaining a string from each message; for each message, obtaining runtime data regarding execution of the application, and associating the runtime data with the string of the message; calculating a distance between the string of each message and the strings of each other message of the plurality of messages by comparing the string of each message and the strings of each other message of the plurality of messages using a message distance algorithm; grouping the strings according to the distances into a plurality of groups, each group has a message group identifier, and each string is associated with one of the message group identifiers; and for each message group identifier, aggregating the runtime data which is associated with the strings which are associated with the message group identifier, so that aggregated runtime data is provided for each group of the plurality of groups.