13. The next window prompts for host credentials, which will be your operating
system username and password, and database credentials, which will be the
SYS username and password. If you want to save these to prevent having to
enter them repeatedly, check the box Save As Preferred Credential. Click
OK
.
Use the Alert Log and Trace Files
The alert log is a continuous record of critical operations applied to the instance and
the database. Its location is determined by the instance parameter BACKGROUND_
DUMP_DEST, and its name is alert_SID.log, where SID is the name of the instance.
The critical operations recorded in the alert log include
• All startup and shutdown commands, including intermediate commands such
as ALTER DATABASE MOUNT
• All errors internal to the instance (for example, any ORA-600 errors)
• Any detected datafile block corruptions
• Any record locking deadlocks that may have occurred
• All operations that affect the physical structure of the database, such as
creating or renaming datafiles and online redo logfiles
• All ALTER SYSTEM commands that adjust the values of initialization parameters
• All log switches and log archives
The alert log entry for a startup shows all the nondefault initialization parameters.
This information, together with the subsequent record of changes to the instance
made with ALTER SYSTEM commands and to the database physical structures made
with ALTER DATABASE commands, means that it is always possible to reconstruct the
history of changes to the database and the instance. This can be invaluable when
trying to backtrack in order to find the source of a problem.
TIP For many DBAs, the first thing they do when they are asked to look at
a database for the first time is locate the alert log and scan through it, just to
get an idea of what has been going on.
Trace files are generated by the various background processes, usually when they
encounter an error. These files are located in the BACKGROUND_DUMP_DEST
directory, along with the alert log. If a background process has failed because of an
error, the trace file generated will be invaluable in diagnosing the problem.
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