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Glossary

Jacek Masiulaniec edited this page Jun 23, 2015 · 115 revisions

aggregator

Central service acting as a publisher of a feed that carries data points pertaining to all hosts. This feed is effectively a union of forwarder and poller feeds.

controller

Central service responsible for cluster management.

data point

Numeric value obtained by reading of a statistic at a specific time. Element of a time series. Every line output by a plugin is a data point.

In a line plot, it corresponds to every (x,y) that contributes to line's shape.

feed

TCP connection carrying real-time stream of recently extracted data points. Produced by forwarder, poller, and aggregator.

filter

Ruleset used to drop data points received from plugins, or to rewrite them before publishing to subscribers.

forwarder

Lightweight agent distributed to every host. Reads data points from plugins and publishes them in a single feed to any subscribers.

plugin

User program running a loop that extracts data points from the local host (if executed by forwarder) or from remote hosts (if executed by poller). It writes these points to standard output, one line per data point. Standard output is typically a pipe to forwarder or poller, which pass the points through a filter and publish the final points to any subscribers.

poller

Central service polling remote hosts, for example SNMP-only devices. Reads data points from plugins and publishes them in a single feed to any subscribers.

statse

Plugin responsible for deriving data points from event streams (e.g. web logs) through continuous statistical aggregation.

subscriber

User program that consumes the feed.

  1. Indirect: receives data points from aggregator.
  2. Direct receives data points from forwarders and the poller.

time series

Historical record of data points created by periodically reading the value of a statistic (e.g. cpu utilization of the local host).

In a line plot, it corresponds to the line itself.

time series identifier

Human-readable name of a time series.

The identifier consists of two sections:

Metric: A dot-delimited string that represents a broad category of time series (e.g. os.filesystem.usage).

Tags: List of key=value pairs that subdivide metric along independent dimensions (e.g. host=localhost,mount=/var/log).

In a line plot, time series identifier corresponds to a label in the legend (key) section.

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