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
|
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 using ``gauge-fn``::
but you have to pass it a function, not just a body::
(require '[metrics.core :refer [new-registry]])
(require '[metrics.gauges :refer [gauge-fn gauge]])
(def reg (new-registry))
(def files-open
(gauge-fn reg "files-open"
#(return-number-of-files-open ...)))
Once a gauge has been registered, a call to ``(gauge reg "files-open")`` will
return the existing gauge.
.. _gauges/defgauge:
You can also use the ``defgauge`` macro to create a gauge and bind it to a var
in one concise, easy step::
(require '[metrics.gauges :refer [defgauge]])
(defgauge reg files-open
(fn []
(return-number-of-files-open ...)))
``defgauge`` takes 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.
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``::
(require '[metrics.gauges :refer [value]])
(value files-open)
Or if you haven't held a reference to ``files-open``, you can do the following::
(value (gauge reg "files-open"))
|
