Web-based applications do not commonly use HTTP error codes to send error information. Instead, they typically send error information within HTML content. In such scenarios, errors are normally detected only when scripts attempt to call links on pages that include error messages rather than their original content. Such attempts typically lead to link not found errors. Such messages generally are insufficient for uncovering the reasons why errors occurred and determining how errors can be reproduced in debugging environments. The only way to track down the causes of such elusive errors is to record error histories under load and determine the actions of the virtual users and the server before the error occurred.
TrueLogs provide this information even when several thousand virtual users are simulated and errors occur only occasionally over long periods of time.
TrueLogs facilitate visual verification under load, which reveals elusive application-level errors that usually are encountered only by subsets of users when applications are under heavy load. For most applications, this sort of load is only experienced once an application is deployed. Typical non-HTTP errors for Web applications include incorrect text on Web pages, incorrect value computations, and application-related messages such as Servlet Error and Server Too Busy.