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

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.