metrics-clojure is a Clojure façade around Coda Hale's metrics library.
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metrics-clojure wraps up the
metrics classes to make them more Clojurey.
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
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 ...)))
Create your counter:
(use '[metrics.counters :only (counter)]) (def users-connected (counter "users-connected"))
Now increment and decrement it:
(use '[metrics.counters :only (inc! dec!)]) (inc! users-connected) (inc! users-connected 2) (dec! users-connected) (dec! users-connected 2)
Create your meter:
(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".
Mark the meter every time the event happens:
(use '[metrics.meters :only (mark!)]) (mark! files-served)
Create your histogram:
(use '[metrics.histograms :only (histogram)]) (def search-results-returned (meter "search-results-returned"))
You can create a biased histogram by passing an extra boolean argument:
(def search-results-returned-biased (meter "search-results-returned-biased" true))
Update the histogram when you have a new value to record:
(use '[metrics.histograms :only (update!)]) (update! search-results-returned 10)
Create your timer:
(use '[metrics.timers :only (timer)]) (def image-processing-time (timer "image-processing-time"))
Now time something:
(use '[metrics.timers :only (time!)]) (time! image-processing-time (process-image-part-1 ...) (process-image-part-2 ...))
time! is a macro. If you need a function instead, you can use
you'll need to pass it a function instead of just a body:
(use '[metrics.timers :only (time-fn!)]) (time-fn! image-processing-time (fn  (process-image-part-1 ...) (process-image-part-2 ...)))
In all these examples we've used a string to name the metric. The
library actually names metrics with three-part names. In Java and Scala those
names are usually the package and class where the timer is being used.
In Clojure you usually won't have a meaningful class name to record, and the
package name would be a pain to find, so
metrics-clojure uses "default" and
"default" for those parts. This results in a name like
If you want to specify something other than "default" you can pass a collection of three strings instead of a single string:
(use '[metrics.timers :only (timer)]) (def response-time (timer ["webservice" "views" "response-time"]))
This will result in a name like "webservice.views.response-time".
You can remove metrics as long as you know their names:
(use '[metrics.core :only (remove-metric)]) (remove-metric "files-served")
You can use the sequence form of metric names here too, of course:
(remove-metric ["webservice" "views" "response-time"])
metrics-clojure only supports reporting metrics through the console
(on standard error):
(use '[metrics.core :only (report-to-console)]) (report-to-console 10)
This will tell
metrics to print all metrics to the console every ten seconds.
More reporting methods will be added in the future. Pull requests are welcome.
Side Effects and Agents
Pretty much everything
metrics-clojure does causes side effects. If you're
recording metrics inside of a
dosync they may be recorded multiple times if
the transaction is restarted.
This may or may not be what you want. If you're recording how long it takes to do something, and you do it twice, then it makes sense to record it each time. If you're recording how many responses get sent to a user, then you probably don't want to overcount them.
metrics-clojure doesn't try to decide for you. It leaves it up to you to
handle the issue.
If you don't want to record something multiple times, an agent may be a good way to handle things:
(def thing-given-to-user (agent (counter "thing-given-to-user"))) (dosync (send inc! thing-given-to-user) (make-thing ...))
This works because the recording functions for counters, meters and histograms return the metric object.
This will not work with timers!
time! returns the result of the work,
so the agent's value will be replaced by that and it won't work more than once.
In practice this shouldn't be a problem though, because if you're timing work you'll probably want to time it every time it happens, right?