Write a message to a trace file or the alert.log file

In case you want to write something to the Oracle alert.log file, you can use an undocumented package procedure to do so.

The dbms_system.ksdwrt package procedure takes 2 arguments, the first parameter is where you want to write the message, indicated by the second parameter to.
The first parameter can take 3 different values:

• 1: Write the message to a trace file
• 2: Write the message to the alert.log file
• 3: Write the message to both a trace file and the alert.log file

For example, your application can write something to the alert.log file whenever a critical condition is encountered.
In order to write something to the alert.log, we need to provide 2 as the first parameter.

SQL> exec dbms_system.ksdwrt(2, '[YOURAPP] A Critical error was detected in module: INIT');

PL/SQL procedure successfully completed.

Now, if we check the alert.log file, we can see the message:

SQL> select value from v$parameter where name='background_dump_dest';

VALUE
--------------------------------------------------------------------------------
/u01/app/oracle/product/10.2.0/rdbms/log

SQL> select name from v$database;

NAME
---------------------------
ORA10G

SQL> host tail /u01/app/oracle/product/10.2.0/rdbms/log/alert_ORA10G.log
Mon Jun 15 21:57:47 2009
[YOURAPP] A Critical error was detected in module: INIT

Starting from Oracle 11g, you can query the X$DBGALERTEXT internal view to check the alert.log from within Oracle.