# metrics-clojure / docs / source / metrics / gauges.rst

 Steve Losh ff65daf 2012-03-17 Steve Losh 41f4d65 2012-03-17 Steve Losh ff65daf 2012-03-17 Steve Losh 41f4d65 2012-03-17 Steve Losh ff65daf 2012-03-17 Steve Losh 41f4d65 2012-03-17 Steve Losh ff65daf 2012-03-17 Steve Losh 41f4d65 2012-03-17 Steve Losh ff65daf 2012-03-17   1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 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 -------- 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 ...))) .. _gauges/defgauge: 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  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. Reading ------- There's only one way to get data from a gauge. .. _gauges/value: value ~~~~~~~~~ You can read the value of a gauge at any time with value:: (use '[metrics.gauges :only (value)]) (value files-open) 
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