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.
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.