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Don Burleson Blog 







Multiple alert logs in RAC

Oracle Database Tips by Donald BurlesonJuly 29, 2015

Question:  Is it one alert log per instance or one per RAC database?  I want to monitor by RAC alerts and I need to know if Oracle has multiple alerts logs in RAC databases.  Are alert logs in the diagnostic_dest instance specific or database specific?  If they are instance specific, how can you consolidate the alert log messages?

Answer:  Yes, each instance in a RAC cluster has it's own alert log.  The 11g RAC Administrator's Guide under Appendix B Troubleshooting notes:

Using Instance-Specific Alert Files in Oracle RAC

Each instance in an Oracle RAC database has one alert file. The alert file for each instance, alert.SID.log, contains important information about error messages and exceptions that occur during database operations. Information is appended to the alert file each time you start the instance. All process threads can write to the alert file for the instance.

The alert_SID.log file is in the directory specified by the DIAGNOSTIC_DEST parameter in the initdb_name.ora initialization parameter file.

For monitoring you alert logs, I use scripts to scan each alert log in the RAC cluster for important messages and e-mail them to a separate location.  If you don't want to write your own custom scripts, see my Oracle script download.

  • In 11g and beyond, you can directly query the alert log with SQL, using x$dbgalertext.

  • SQL against the alert log - You can define the alert log file as an external table and detect important messages with SQL and e-mail them to a central repository.

  • Scripts - You can write Oracle shell scripts OS shell scripts to detect alert log messages. 

  • Ion - The Ion tool has complete mechanisms for setting custom alert log extracts.

  • PL/SQL - You can write a SQL*Plus procedure using utl_file to read the alert log.

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