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diff --git a/src/web/api/queries/des/README.md b/src/web/api/queries/des/README.md new file mode 100644 index 000000000..6dc19e732 --- /dev/null +++ b/src/web/api/queries/des/README.md @@ -0,0 +1,77 @@ +<!-- +title: "double exponential smoothing" +sidebar_label: "double exponential smoothing" +custom_edit_url: https://github.com/netdata/netdata/edit/master/src/web/api/queries/des/README.md +learn_status: "Published" +learn_topic_type: "References" +learn_rel_path: "Developers/Web/Api/Queries" +--> + +# double exponential smoothing + +Exponential smoothing is one of many window functions commonly applied to smooth data in signal +processing, acting as low-pass filters to remove high frequency noise. + +Simple exponential smoothing does not do well when there is a trend in the data. +In such situations, several methods were devised under the name "double exponential smoothing" +or "second-order exponential smoothing.", which is the recursive application of an exponential +filter twice, thus being termed "double exponential smoothing". + +In simple terms, this is like an average value, but more recent values are given more weight +and the trend of the values influences significantly the result. + +> **IMPORTANT** +> +> It is common for `des` to provide "average" values that far beyond the minimum or the maximum +> values found in the time-series. +> `des` estimates these values because of it takes into account the trend. + +This module implements the "Holt-Winters double exponential smoothing". + +Netdata automatically adjusts the weight (`alpha`) and the trend (`beta`) based on the number +of values processed, using the formula: + +``` +window = max(number of values, 15) +alpha = 2 / (window + 1) +beta = 2 / (window + 1) +``` + +You can change the fixed value `15` by setting in `netdata.conf`: + +``` +[web] + des max window = 15 +``` + +## how to use + +Use it in alerts like this: + +``` + alarm: my_alert + on: my_chart +lookup: des -1m unaligned of my_dimension + warn: $this > 1000 +``` + +`des` 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=des` in the URL. + +## Examples + +Examining last 1 minute `successful` web server responses: + +-  +-  +-  +-  +-  + +## References + +- <https://en.wikipedia.org/wiki/Exponential_smoothing>. + + |