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Median

The median is the value separating the higher half from the lower half of a data sample (a population or a probability distribution). For a data set, it may be thought of as the "middle" value.

median is not an accurate average. However, it eliminates all spikes, by sorting all the values in a period, and selecting the value in the middle of the sorted array.

Netdata also supports trimmed-median, which trims a percentage of the smaller and bigger values prior to finding the median. The following trimmed-median functions are defined:

  • trimmed-median1
  • trimmed-median2
  • trimmed-median3
  • trimmed-median5
  • trimmed-median10
  • trimmed-median15
  • trimmed-median20
  • trimmed-median25

The function trimmed-median is an alias for trimmed-median5.

how to use

Use it in alarms like this:

 alarm: my_alarm
    on: my_chart
lookup: median -1m unaligned of my_dimension
  warn: $this > 1000

median does not change the units. For example, if the chart units is requests/sec, the result will be again expressed in the same units.

It can also be used in APIs and badges as &group=median in the URL. Additionally, a percentage may be given with &group_options= to trim all small and big values before finding the median.

Examples

Examining last 1 minute successful web server responses:

References