# Gauges

Gauges are used to measure the instantaneous value of something.

They're often useful for things that aren't events, like "users currently in the database". If you can perform a query of some kind at any time to get a value, it's probably something suitable for a gauge.

Examples of metrics you might want to track with a gauge:

• Number of users in your database.

TODO: More examples.

## Creating

(use '[metrics.gauges :only (gauge)])

(def files-open
(gauge "files-open"
(return-number-of-files-open ...)))


That's it. Pretty simple.

gauge is a macro. If you need a function instead you can use gauge-fn, but you have to pass it a function, not just a body:

(use '[metrics.gauges :only (gauge-fn)])

(def files-open
(gauge-fn "files-open"
#(return-number-of-files-open ...)))


You can also use the defgauge macro to create a gauge and bind it to a var in one concise, easy step:

(use '[metrics.gauges :only (defgauge)])

(defgauge files-open
(return-number-of-files-open ...))


defgauge can take a body of statements like gauge or a function like gauge-fn.

All the def[metric] macros do some :ref:magic <desugaring> to the metric title to make it easier to define.

## Writing

With gauges there is no writing. Gauges execute the form(s) (or function) you passed when creating them every time they're read. You don't need to do anything else.

(use '[metrics.gauges :only (value)])