Github user uce commented on a diff in the pull request:
https://github.com/apache/flink/pull/2158#discussion_r69166838
--- 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.
+
+### Scope
--- End diff --
I was wondering whether the names are case sensitive or not?
---
If your project is set up for it, you can reply to this email and have your
reply appear on GitHub as well. If your project does not have this feature
enabled and wishes so, or if the feature is enabled but not working, please
contact infrastructure at infrastruct...@apache.org or file a JIRA ticket
with INFRA.
---
