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.
Create your gauge:
(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.
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.
There's only one way to get data from a gauge.
You can read the value of a gauge at any time with value:
(use '[metrics.gauges :only (value)]) (value files-open)