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Date: Thu, 30 Jun 2016 16:16:10 +0000 (UTC)
From: "ASF GitHub Bot (JIRA)" <jira@apache.org>
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Subject: [jira] [Commented] (FLINK-4116) Document metrics
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archived-at: Thu, 30 Jun 2016 16:16:12 -0000


    [ https://issues.apache.org/jira/browse/FLINK-4116?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15357374#comment-15357374 ] 

ASF GitHub Bot commented on FLINK-4116:
---------------------------------------

Github user zentol commented on a diff in the pull request:

    https://github.com/apache/flink/pull/2158#discussion_r69163312
  
    --- 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.
    --- End diff --
    
    no, reporters generally use toString() on the value returned. that should probably be documented though.


> 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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