One of the most important abilities needed for a DBA is the ability to diagnose database problems. The data dictionary is often used for this task. However, Oracle has several other tools that we can use to diagnose problems, including logfiles, trace files, and the Automatic Diagnostic Repository.
The most primary diagnostic tool used by DBAs is the database alert log . The alert log is a plain text log (with an exception for Version 11g that we will discuss shortly) that contains both messages and errors regarding the functioning of the database. As such, many DBAs consider the alert log to be the "first stop" when attempting to diagnose a database problem.
Up until Oracle Version 11g, the alert log was stored in a standard directory. This directory is usually referred to as the BDUMP
directory, for background dump. This directory held the alert log as well as files known as trace files, particularly those for the...