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https://issues.apache.org/jira/browse/FLINK-4116?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15357386#comment-15357386
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ASF GitHub Bot commented on FLINK-4116:
---------------------------------------
Github user uce commented on a diff in the pull request:
https://github.com/apache/flink/pull/2158#discussion_r69163863
--- Diff: docs/apis/common/index.md ---
@@ -1350,3 +1350,397 @@ You may specify program arguments before the job is
executed. The plan visualiza
the execution plan before executing the Flink job.
{% top %}
+
+Metrics
+-------------------
+
+Flink exposes a metric system that allows gathering and exposing metrics
to external systems.
+
+### Registering metrics
+
+You can access the metric system from any user function that extends
[RichFunction]({{ site.baseurl }}/apis/common/index.html#rich-functions) by
calling `getRuntimeContext().getMetricGroup()`.
+This method returns a `MetricGroup` object on which you can create and
register new metrics.
+
+### Metric types
+
+Flink supports `Counters`, `Gauges` and `Histograms`.
+
+#### Counter
+
+A `Counter` is used to count something. The current value can be in- or
decremented using `inc()/inc(long n)` or `dec()/dec(long n)`.
+You can create and register a `Counter` by calling `counter(String name)`
on a MetricGroup.
+
+{% highlight java %}
+
+public class MyMapper extends RichMapFunction<String, Integer> {
+ private Counter counter;
+
+ @Override
+ public void open(Configuration config) {
+ // create and register a counter
+ this.counter =
getRuntimeContext().getMetricGroup().counter("myCounter");
+ ...
+ }
+
+ @public Integer map(String value) throws Exception {
+ // increment counter
+ this.counter.inc();
+ ...
+ }
+}
+
+{% endhighlight %}
+
+Alternatively you can also use your own `Counter` implementation:
+
+{% highlight java %}
+
+public class MyMapper extends RichMapFunction<String, Integer> {
+ ...
+
+ @Override
+ public void open(Configuration config) {
+ // register a custom counter
+ this.counter =
getRuntimeContext().getmetricGroup().counter("myCustomCounter", new
CustomCounter());
+ ...
+ }
+ ...
+}
+
+{% endhighlight %}
+
+#### Gauge
+
+A `Gauge` provides a value of any type on demand. In order to use a
`Gauge` you must first create a class that implements the
`org.apache.flink.metrics.Gauge` interface.
+There is not restriction for the type of the returned value.
+You can register a gauge by calling `gauge(String name, Gauge gauge)` on a
MetricGroup.
+
+{% highlight java %}
+
+public class MyMapper extends RichMapFunction<String, Integer> {
+ private int valueToExpose;
+
+ @Override
+ public void open(Configuration config) {
+ // register the gauge
+ getRuntimeContext().getmetricGroup().gauge("MyGauge", new
Gauge<Integer>() {
+ @Override
+ public Integer getValue() {
+ return valueToExpose;
+ }});
+ ...
+ }
+ ...
+}
+
+{% endhighlight %}
+
+#### Histogram
+
+A Histogram measure the distribution of long values.
+You can register one by calling histogram(String name, Histogram
histogram) on a MetricGroup.
+
+{% highlight java %}
+public class MyMapper extends RichMapFunction<Long, Integer> {
+ private Histogram histogram;
+
+ @Override
+ public void open(Configuration config) {
+ // create and register a counter
+ this.histogram =
getRuntimeContext().getMetricGroup().histogram("myHistogram", new
MyHistogram());
+ ...
+ }
+
+ @public Integer map(Long value) throws Exception {
+ this.histogram.update(value);
+ ...
+ }
+}
+{% endhighlight %}
+
+Flink only provides an interface for Histograms, but offers a Wrapper that
allows usage of Codahale/DropWizard Histograms.
(org.apache.flink.dropwizard.metrics.DropWizardHistogramWrapper)
+This wrapper is contained in the `flink-metrics-dropwizard` module.
--- End diff --
- Link to how a user can add this module
- I would also add an example for this actually (as everyone who wants to
use Histogram will need this)
> Document metrics
> ----------------
>
> Key: FLINK-4116
> URL: https://issues.apache.org/jira/browse/FLINK-4116
> Project: Flink
> Issue Type: Improvement
> Components: Documentation, Metrics
> Affects Versions: 1.1.0
> Reporter: Chesnay Schepler
> Assignee: Chesnay Schepler
> Fix For: 1.1.0
>
>
> The metric system is currently not documented, which should be fixed before
> the 1.1 release.
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