Channel Types

Channel Type setting completely changes the style of how raw values are processed to calculate channel's Primary Data Points. There are four channel types:

• Gauge
• Counter
• Derive
• Absolute

Value of Primary Data Point equals to the channel Expression evaluation result, i.e. the only conversion is application of NULL Value Processing and Out Of Range Value Processing rules.

This type is suitable for simple metering like temperature, number of people in the room or stock price.

Suitable for continuous incrementing counters. The Counter data source assumes that the counter never decreases, except when a counter overflows. The statistics update function takes the overflow into account. The counter is stored as a per-second rate. When the counter overflows, channel checks if the overflow happened at the 32bit or 64bit border and acts accordingly by adding an appropriate value to the result.

Simply speaking, Counter will look at the difference between the previous value and the current value (the delta). An example would be an odometer. The Primary Data Point is computed as: delta(counter) divided by delta(time).

Examples of counters:

- Vehicle travel distance (number of meters passed by the vehicle)

- Error count (number of errors occurred since device startup)

- Interface traffic (number of ingress/egress bytes on the interface since network device power up).

- CPU load caused by a process (number of milliseconds of CPU time consumed by the process since its startup)

Derive-type channel can measure both increments and decrements. This can be useful for gauges, for example, to measure the rate of people entering or leaving a room. Internally, derive works exactly like Counter but without overflow checks. So if your counter does not reset at 32 or 64 bit you might want to use Derive and combine it with a Minimum Value of 0.

Derive is really similar to Counter, but now it can also go back. An example could be something monitoring a bidirectional pump. The resulting pumping rate can be negative as well as positive.

Absolute channels are used for counters which get reset upon reading. This is used for fast counters which tend to overflow. So instead of reading them normally you reset them after every read to make sure you have a maximum time available before the next overflow. Another usage is for things you count like number of messages since the last update.

Absolute channel is also similar to the odometer, but here the counter is reset every time it is read. Primary Data Point computed as: value divided by delta(time).

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