10 Metrics
Viewing metric data
Metric data created by the controller and applications can assist you when you are troubleshooting
issues with the controller or network.
The curl commands in this section interact with the
metrics/apps
REST API to display
information about metric data collected by the controller. These commands must be used on
individual controllers; they do not return information from controller teams.
About metrics
Metrics are created by controller components or applications and can be of several different
types, such as timers, counters, gauges, and histograms.
How metric values are processed
When the controller component or application creates a metric, it specifies what to do with the
resulting metric values. Metric values can be processed in one or more of the following ways:
•
They can be persisted to disk as a time-series of values.
•
They can be exposed for inspection by the user via JMX.
•
They can be retained in memory for internal use by the component or application.
For metric values that are persisted to disk:
•
The time-series values for each individual metric can be persisted at intervals of 1, 5, or 15
minutes. Controller administrators configure the default persistence interval using the
MetricManagerComponent
controller component. A controller component or application
that creates a metric can override the default persistence interval for that metric.
•
Each persisted value represents the value of the metric over the elapsed persistence interval.
For example, for a counter that increments from 100 to 145 during a 5-minute interval, the
persisted value for the interval is 45, which is the value of the counter at the start of the
interval subtracted from the value of the counter at the end of the interval. For each type of
metric, there is a different method of computing the persisted value.
•
Because some metric values are not updated at a steady rate, the persisted information for
a metric value includes the raw value and the time over which the value accrued. Providing
this information enables the metric viewer to normalize data. For example if the counter
value was updated only during the last 3 minutes of the 5-minute interval for which it was
persisted:
◦
The raw value accrued over the interval is 45, which is the value at the start of the
interval subtracted from the value at the end of the interval.
◦
The persisted value includes both the raw value and the time over which the data was
accrued, which is 3 minutes.
◦
The persistence interval configured for the metric is 5 minutes.
◦
A normalized rate of accrual over the interval is 15 increments per minute (45 increments
divided by 3 minutes) or 75 for the entire 5-minute interval.
•
Controller administrators use
MetricManagerComponent
controller component to configure
the length of time the controller retains persisted metric values on disk. Controller components
and applications cannot override this retention period.
Viewing metric data
141