python.d changefinder

Plugin: python.d.plugin Module: changefinder

Overview

This collector uses the Python changefinder library to perform online changepoint detection on your Netdata charts and/or dimensions.

Instead of this collector just collecting data, it also does some computation on the data it collects to return a changepoint score for each chart or dimension you configure it to work on. This is an online machine learning algorithm so there is no batch step to train the model, instead it evolves over time as more data arrives. That makes this particular algorithm quite cheap to compute at each step of data collection (see the notes section below for more details) and it should scale fairly well to work on lots of charts or hosts (if running on a parent node for example).

Notes - It may take an hour or two (depending on your choice of `n_score_samples`) for the collector to ‘settle’ into it’s

typical behaviour in terms of the trained models and scores you will see in the normal running of your node. Mainly this is because it can take a while to build up a proper distribution of previous scores in over to convert the raw score returned by the ChangeFinder algorithm into a percentile based on the most recent n_score_samples that have already been produced. So when you first turn the collector on, it will have a lot of flags in the beginning and then should ‘settle down’ once it has built up enough history. This is a typical characteristic of online machine learning approaches which need some initial window of time before they can be useful.

As this collector does most of the work in Python itself, you may want to try it out first on a test or development system to get a sense of its performance characteristics on a node similar to where you would like to use it.
On a development n1-standard-2 (2 vCPUs, 7.5 GB memory) vm running Ubuntu 18.04 LTS and not doing any work some of the typical performance characteristics we saw from running this collector (with defaults) were:
- A runtime (netdata.runtime_changefinder) of ~30ms.
- Typically ~1% additional cpu usage.
- About ~85mb of ram (apps.mem) being continually used by the python.d.plugin under default configuration.

This collector is supported on all platforms.

This collector supports collecting metrics from multiple instances of this integration, including remote instances.

Default Behavior

Auto-Detection

By default this collector will work over all system.* charts.

Limits

The default configuration for this integration does not impose any limits on data collection.

Performance Impact

The default configuration for this integration is not expected to impose a significant performance impact on the system.

Setup

Prerequisites

Python Requirements

This collector will only work with Python 3 and requires the packages below be installed.

# become netdata user
sudo su -s /bin/bash netdata
# install required packages for the netdata user
pip3 install --user numpy==1.19.5 changefinder==0.03 scipy==1.5.4

Note: if you need to tell Netdata to use Python 3 then you can pass the below command in the python plugin section of your netdata.conf file.

[ plugin:python.d ]
  # update every = 1
  command options = -ppython3

Configuration

File

The configuration file name for this integration is python.d/changefinder.conf.

You can edit the configuration file using the edit-config script from the Netdata config directory.

cd /etc/netdata 2>/dev/null || cd /opt/netdata/etc/netdata
sudo ./edit-config python.d/changefinder.conf

Options

There are 2 sections:

Global variables
One or more JOBS that can define multiple different instances to monitor.

The following options can be defined globally: priority, penalty, autodetection_retry, update_every, but can also be defined per JOB to override the global values.

Additionally, the following collapsed table contains all the options that can be configured inside a JOB definition.

Every configuration JOB starts with a job_name value which will appear in the dashboard, unless a name parameter is specified.

Name	Description	Default	Required
charts_regex	what charts to pull data for - A regex like `system\../` or `system\../apps.cpu/apps.mem` etc.	system..*	True
charts_to_exclude	charts to exclude, useful if you would like to exclude some specific charts. note: should be a ‘,’ separated string like ‘chart.name,chart.name’.		False
mode	get ChangeFinder scores ‘per_dim’ or ‘per_chart’.	per_chart	True
cf_r	default parameters that can be passed to the changefinder library.	0.5	False
cf_order	default parameters that can be passed to the changefinder library.	1	False
cf_smooth	default parameters that can be passed to the changefinder library.	15	False
cf_threshold	the percentile above which scores will be flagged.	99	False
n_score_samples	the number of recent scores to use when calculating the percentile of the changefinder score.	14400	False
show_scores	set to true if you also want to chart the percentile scores in addition to the flags. (mainly useful for debugging or if you want to dive deeper on how the scores are evolving over time)	False	False

Examples

Default

Default configuration.

local:
  name: 'local'
  host: '127.0.0.1:19999'
  charts_regex: 'system\..*'
  charts_to_exclude: ''
  mode: 'per_chart'
  cf_r: 0.5
  cf_order: 1
  cf_smooth: 15
  cf_threshold: 99
  n_score_samples: 14400
  show_scores: false

Metrics

Metrics grouped by scope.

The scope defines the instance that the metric belongs to. An instance is uniquely identified by a set of labels.

Per python.d changefinder instance

This scope has no labels.

Metrics:

Metric	Dimensions	Unit
changefinder.scores	a dimension per chart	score
changefinder.flags	a dimension per chart	flag

Alerts

There are no alerts configured by default for this integration.

Troubleshooting

Debug Mode

To troubleshoot issues with the changefinder collector, run the python.d.plugin with the debug option enabled. The output should give you clues as to why the collector isn’t working.

Navigate to the plugins.d directory, usually at /usr/libexec/netdata/plugins.d/. If that’s not the case on your system, open netdata.conf and look for the plugins setting under [directories].
```
cd /usr/libexec/netdata/plugins.d/
```
Switch to the netdata user.
```
sudo -u netdata -s
```
Run the python.d.plugin to debug the collector:
```
./python.d.plugin changefinder debug trace
```