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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (FLINK-4116) Document metrics
Date Mon, 27 Jun 2016 11:41:52 GMT

    [ https://issues.apache.org/jira/browse/FLINK-4116?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15350834#comment-15350834
] 

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

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

    https://github.com/apache/flink/pull/2158#discussion_r68562298
  
    --- Diff: docs/apis/common/index.md ---
    @@ -1350,3 +1350,211 @@ 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 users gather and expose 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.
    +
    +If you want to count the number of records your user function has received you could
use a Counter like this:
    +
    +{% 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 %}
    +
    +### Metric types
    +
    +Flink supports Counters, Gauges and Histograms.
    +
    +A Counter is used to count something. The current value can be in- or decremented using
`inc([long n])` or `dec([long n])`.
    --- End diff --
    
    I've never seen the notation `inc([long n])` in the Flink documentation. Maybe it's better
to specify the parameterless and the parameter variant explicitly.


> 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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