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Lesson 3Types of alert log messages
Objective Identify the main types of alert log messages.

Types of alert log messages

The Oracle alert log contains several types of informative messages. While all of the alert log messages provide information about events within the Oracle database, we'll look at these messages according to the severity of the situation.

Informational Messages

The alert log was originally created by Oracle to hold internal messages about the status of the database. As such, we see the following "noise" messages in the alert log messages that are informational in nature and that are not necessarily important to monitor.
These include:
  1. Startup and shutdown messages
  2. Log switch messages

Task termination messages

These messages indicate an individual task that does not hurt the overall Oracle database. These messages include:
  1. Failure to extend a rollback segment
  2. Snapshot too old message

Diagnostic Events

These are set as init.ora parameters or with the ALTER SYSTEM SET EVENTS command.

Serious Oracle messages

In addition, you will also see important error messages that indicate the status of the database and the tasks that are executing within the database. Sometimes these messages will be found when the database crashes, and other times the database will continue to run after a serious message. These include:
  1. Corrupt Oracle blocks (ORA-1578)
  2. Unknown serious error (ORA-600)
  3. Internal error (ORA-7445)

The alert file grows over time

The alert log is a never-ending file in that new messages are always appended to the end of the existing alert log file. Over a period of a year, an alert log file can become quite large, so the Oracle DBA will periodically purge the alert log. Oracle will automatically re-initialize the alert.log file the next time a message needs to be written.
In the next two lessons, you will take a closer look at the messages in the alert log and learn what to do when you find them.