Remove hopelessly outdated tutorial.

documentation/tutorials/metric_model.md

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-# Introduction
-
-Prometheus is in the business of doing several things:
-
-  * exposing metrics,
-  * collecting metrics,
-  * performing computational rules upon them and generating synthetic series,
-  * triggering events based upon rule conditions, and
-  * metric series archival and deletion.
-
-The focus of this guide is oriented exclusively toward exposing metrics with
-an eye toward computational rules and event handling in the Prometheus core.
-
-After reading this guide, you will understand the following:
-
-  * what types of Prometheus metrics are available and how they work,
-  * how you should embed these metrics in your applications,
-  * what metadata you attach to them, and
-  * what to instrument.
-
-# Metric Types
-
-Prometheus offers three core metric types:
-
-  * counters,
-  * gauges, and
-  * summaries.
-
-Each is tailored toward a different purpose, so it is important to use the
-right one for the right job.
-
-## Counter
-
-A _Counter_ tracks addition or subtraction of values from itself.  It is used
-to represent state that you control and is not external.
-
-The following are good examples or applications of counters:
-
-  * pedometers: devices that track the number of steps you take,
-  * tickers: devices that measure the number of times an event has occurred,
-  * censuses: processes to count to number of individuals of a population, and
-  * _your_ bank account ledger: the sum of all transactions conducted on your
-    liquid assets.
-
-The key thing to note about _Counters_ is that they are best used when you are
-directly receiving the events that mutate their values and mutating the
-underlying values that represent their individual state.
-
-A good example is of an elevator that tracks how many times it has been used in
-its duty cycle.  Each time someone hits the button to dispatch it, the elevator
-can update its tally; and this is a tally it keeps!
-
-See also the [counter Javadoc](https://github.com/prometheus/client_java/blob/master/client/src/main/java/io/prometheus/client/metrics/Counter.java)
-in Prometheus' Java client library for further documentation and concrete code
-examples.
-
-## Gauges
-
-A _Gauge_ reports instantaneous values based on external state.  This is
-primarily state that you do not control directly but rather that you depend on
-or can inspect.
-
-The following are good examples or applications of gauges:
-
-  * thermometer,
-  * barometer,
-  * altimeter, and
-  * total system resource utilization.
-
-Unlike a _Counter_, you don't have direct access to the events that brought the
-_Gauge_ to its value today.  This is a white-box and black-box distinction.
-
-See also the [gauge Javadoc](https://github.com/prometheus/client_java/blob/master/client/src/main/java/io/prometheus/client/metrics/Gauge.java)
-in Prometheus' Java client library for further documentation and concrete code
-examples.
-
-## Which to use: Counter or Gauge?
-Knowing whether to use a _Counter_ or a _Gauge_ can be tough.  Let's perform a
-practical thought exercise.  Below is an image of an automobile's instrument
-dashboard:
-
-![Vehicle Instrument Console](dashboard.jpg "Vehicle Instrument Console")
-
-What do you see in this photo?  Take a minute to make a list.  (Don't worry;
-I'll wait for you.)
-
-From left to right and top to bottom, there are the following instruments:
-
-  * Tachometer: it measures the revolutions per minute of the engine;
-  * Clock: it measures the time;
-  * Thermometer: it measures the temperature outside the vehicle;
-  * Odometer: they measure the total miles the vehicle has traveled as well as
-    how far it has traveled on its last trip;
-  * Fuel Gauge: it measures how much fuel is in the tank;
-  * Speedometer: it measures how fast we are going.
-
-Great!  Look at this list and now think about the definitions above for
-_Counter_ and _Gauge_.  Can you identify what instruments are what?  (Again,
-I'll wait for you.)
-
-  * Tachometer: Counter.  Tricky.  The vehicle's sensors observe how quickly
-    the flywheel rotates and update the instrument's value on frequent
-    intervals by counting revolutions.
-  * Clock: Gauge.  It is an external value, and we cannot watch the clock's
-    internal events.
-  * Thermometer: Gauge.  It measures an external value, and there is no way to
-    track thermodynamic events that influence the outside temperature.
-  * Odometer: Counter.  It measures distances by the number of times the
-    wheels have turned, which itself is based on an event.
-  * Fuel Gauge: Gauge.  Who would have guessed?  It uses a floating ballast and
-    a rheostat and is not event-based.
-  * Speedmeter: Counter.  Tricky.  It measures wheel rotation (events) over
-    time.
-
-## Summaries
-
-_Summary_ is a unique metric type, and one you have probably not used before.
-It samples events over sliding windows of time and provides instantaneous
-insight into their distributions, frequencies, and sums.
-
-Practically speaking, a summary collects event values and reports the
-following information:
-
-  * streaming quantile values of the entire observed population,
-  * the total sum of all observed values, and
-  * the count of events that have been observed.
-
-This is quite convenient, for if you are interested in tracking latencies of an
-operation in real time, you get three types of information reported for free
-with one metric.
-
-See also the [summary Javadoc](https://github.com/prometheus/client_java/blob/master/client/src/main/java/io/prometheus/client/metrics/Summary.java)
-in Prometheus' Java client library for further documentation and concrete code
-examples.
-
-# Acknowledgements
-Robert Bray: Vehicle Instrument Panel