# Meters

Meters are metrics that let you "mark" when something happens and tell you how often it occurs.

## Creating

(use '[metrics.meters :only (meter)])

(def files-served (meter "files-served" "files"))


The second argument to meter is a string describing the "units" for the meter. In this example it's "files", as in "18732 files".

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

(use '[metrics.meters :only (defmeter)])

(defmeter files-served "files")


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

## Writing

Mark the meter every time the event happens:

(use '[metrics.meters :only (mark!)])

(mark! files-served)


There are a few functions you can use to retrieve the rate at which the metered events occur.

### rates

You can get a map containing the mean rates of the event considering the last one, five, and fifteen minute periods with rates:

(use '[metrics.meters :only (rates)])

(rates files-served)
=> { 1 100.0,
5 120.0,
15 76.0}


In this example the event happened approximately 100 times per second during the last one minute period, 120 times per second in the last five minute period, and 76 times per second in the last fifteen minute period.

### rate-one

If you only care about the rate of events during the last minute you can use rate-one:

(use '[metrics.meters :only (rate-one)])

(rate-one files-served)
=> 100.0


### rate-five

If you only care about the rate of events during the last five minutes you can use rate-five:

(use '[metrics.meters :only (rate-five)])

(rate-five files-served)
=> 120.0


### rate-fifteen

If you only care about the rate of events during the last fifteen minutes you can use rate-fifteen:

(use '[metrics.meters :only (rate-fifteen)])

(rate-fifteen files-served)
=> 76.0


### rate-mean

If you really want the mean rate of events over the lifetime of the meter (hint: you probably don't) you can use rate-mean:

(use '[metrics.meters :only (rate-mean)])

(rate-mean files-served)
=> 204.123

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