Merging upstream version 1.46.3.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 97 insertions, 0 deletions

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+<!--
+title: "standard deviation (`stddev`)"
+sidebar_label: "standard deviation (`stddev`)"
+custom_edit_url: https://github.com/netdata/netdata/edit/master/src/web/api/queries/stddev/README.md
+learn_status: "Published"
+learn_topic_type: "References"
+learn_rel_path: "Developers/Web/Api/Queries"
+-->
+
+# standard deviation (`stddev`)
+
+The standard deviation is a measure that is used to quantify the amount of variation or dispersion
+of a set of data values.
+
+A low standard deviation indicates that the data points tend to be close to the mean (also called the
+expected value) of the set, while a high standard deviation indicates that the data points are spread
+out over a wider range of values.
+
+## how to use
+
+Use it in alerts like this:
+
+```
+ alarm: my_alert
+    on: my_chart
+lookup: stddev -1m unaligned of my_dimension
+  warn: $this > 1000
+```
+
+`stdev` does not change the units. For example, if the chart units is `requests/sec`, the standard
+deviation will be again expressed in the same units. 
+
+It can also be used in APIs and badges as `&group=stddev` in the URL.
+
+## Examples
+
+Examining last 1 minute `successful` web server responses:
+
+-   ![](https://registry.my-netdata.io/api/v1/badge.svg?chart=web_log_nginx.response_statuses&dimensions=success&group=min&after=-60&label=min)
+-   ![](https://registry.my-netdata.io/api/v1/badge.svg?chart=web_log_nginx.response_statuses&dimensions=success&group=average&after=-60&label=average&value_color=yellow)
+-   ![](https://registry.my-netdata.io/api/v1/badge.svg?chart=web_log_nginx.response_statuses&dimensions=success&group=stddev&after=-60&label=standard+deviation&value_color=orange)
+-   ![](https://registry.my-netdata.io/api/v1/badge.svg?chart=web_log_nginx.response_statuses&dimensions=success&group=max&after=-60&label=max)
+
+## References
+
+Check <https://en.wikipedia.org/wiki/Standard_deviation>.
+
+---
+
+# Coefficient of variation (`cv`)
+
+> This query is also available as `rsd`.
+
+The coefficient of variation (`cv`), also known as relative standard deviation (`rsd`),
+is a standardized measure of dispersion of a probability distribution or frequency distribution.
+
+It is defined as the ratio of the **standard deviation** to the **mean**.  
+
+In simple terms, it gives the percentage of change. So, if the average value of a metric is 1000
+and its standard deviation is 100 (meaning that it variates from 900 to 1100), then `cv` is 10%.
+
+This is an easy way to check the % variation, without using absolute values.
+
+For example, you may trigger an alert if your web server requests/sec `cv` is above 20 (`%`)
+over the last minute. So if your web server was serving 1000 reqs/sec over the last minute,
+it will trigger the alert if had spikes below 800/sec or above 1200/sec.
+
+## how to use
+
+Use it in alerts like this:
+
+```
+ alarm: my_alert
+    on: my_chart
+lookup: cv -1m unaligned of my_dimension
+ units: %
+  warn: $this > 20
+```
+
+The units reported by `cv` is always `%`.
+
+It can also be used in APIs and badges as `&group=cv` in the URL.
+
+## Examples
+
+Examining last 1 minute `successful` web server responses:
+
+-   ![](https://registry.my-netdata.io/api/v1/badge.svg?chart=web_log_nginx.response_statuses&dimensions=success&group=min&after=-60&label=min)
+-   ![](https://registry.my-netdata.io/api/v1/badge.svg?chart=web_log_nginx.response_statuses&dimensions=success&group=average&after=-60&label=average&value_color=yellow)
+-   ![](https://registry.my-netdata.io/api/v1/badge.svg?chart=web_log_nginx.response_statuses&dimensions=success&group=cv&after=-60&label=coefficient+of+variation&value_color=orange&units=pcent)
+-   ![](https://registry.my-netdata.io/api/v1/badge.svg?chart=web_log_nginx.response_statuses&dimensions=success&group=max&after=-60&label=max)
+
+## References
+
+Check <https://en.wikipedia.org/wiki/Coefficient_of_variation>.
+
+