Spotlight on Oracle 10.5 - Release Notes

CPU shows the rate (in milliseconds per second) at which CPU time is consumed by each service for all sessions on the database. Among the services deployed are:

• A default Oracle database service.
• The internal SYS$BACKGROUND service used by background processes.
• The internal SYS$USERS service for user sessions not associated with an application service.

The aggregated CPU time for all services cannot exceed (1000 ms/s) x (the number of CPUs on the cluster).

DB Time shows the rate (in milliseconds per second) at which elapsed time is spent in database user calls by the specified services.

DB time includes all wait time, and does not have the same limitations as CPU time. Because in theory ALL sessions may be waiting at the same time, the aggregated DB Time for all services can be as much as (1000 ms/s) x (the number of sessions connected).

There will always be some sessions connected on each instance in the cluster — even before a user logs in.

Logical Reads shows the rate of logical reads for the specified services across the instances in the Oracle RAC cluster.

A logical read occurs when Oracle finds data in the local buffer cache of an instance without needing to read the data from physical disk. The rate of logical reads can be used to measure the balance between the instances in a cluster.

• The X-axis displays Units per Second for each chart.
• The list of services is arranged on the Y-axis.
• There are separate data series for each database instance in the Oracle RAC cluster.