By Courtney Llamas on Feb 18, 2014
One of the most critical events to monitor on an Oracle Database is your archive area. If the archive area fills up, your database will halt until it can continue to archive the redo logs. If your archive destination is set to a file system, then the Archive Area % Used metric is often the best way to go. This metric allows you to monitor a particular file system for the percentage space that has been used. However, there are a couple of things to be aware of for this critical metric.
Cluster Database vs. Database Instance
You will notice in EM 12c, the Archive Area metric exists on both the Cluster Database and the Database Instance targets. The majority of Cluster Databases (RAC) are built against database best practices which indicate that the Archive destination should be shared read/write between all instances. The purpose for this is that in case of recovery, any instance can perform the recovery and has all necessary archive logs to do so. Monitoring this destination for a Cluster Database at the instance level caused duplicate alerts and notifications, as both instances would hit the Warning/Critical threshold for Archive Area % Used within minutes of each other. To eliminate duplicate notifications, the Archive Area % Used metric for Cluster Databases was introduced. This allows the archive destination to be monitored at a database level, much like tablespaces are monitored in a RAC database.
In the Database Instance (RAC Instance) target, you will notice the Archive Area % Used metric collection schedule is set to Disabled.
If you have a RAC database and you do not share archive destinations between instances, you will want to Disable the Cluster Database metric, and enable the Database Instance metric to ensure that each destination is monitored individually.