1. A method for analysing computer system behavior comprising the steps of: a) detecting first actual computer system behaviors occurring during first run time executions in the computer system of operations including store operations, retrieve operations, create operations, delete operations and make directory operations; b) storing, respective records of valid traces relating to the computer system execution responsive to detecting that ones of the respective first run times resulted in respective valid system executions, wherein the records are stored in respective sets corresponding to valid system executions of the respective store, retrieve, create, delete and make directory operations; c) recording, during a second run time execution for the computer system, second actual computer system behavior as a record of traces of the computer system execution, the first and second behaviors being selected from among behaviors including: i) sequences of functions called during run times, ii) conditions evaluated as true during run times, iii) conditions evaluated as false during run times, iv) loops encountered and numbers of iterations of the encountered loops during run times, and v) goto statements encountered that affect execution flow during run times; d) detecting a failure for the second run time execution, wherein the second run time execution is an execution of a type of operation selected from a group including a store operation, a retrieve operation and a delete operation; e) responsive to the failure detection in d), comparing, by the computer system, the trace record of the second behavior to a selected one of the sets of the trace records of the first behaviors, wherein the selected set is for the same type of operation as the operation of the second run time execution; f) selecting one of the first behavior trace records responsive to the comparing in e), wherein the selected first behavior trace record has, in comparison to the trace record of the second behavior, fewer differences than any of the other trace records of the selected first behavior trace record set; and g) determining and presenting one or more differences between the selected one of the first behavior trace records and the trace record of the second behavior, wherein the one more differences between the selected one of the first behavior trace records and the trace record of the second behavior indicate a cause of the detected failure.