Github user tillrohrmann commented on a diff in the pull request:
https://github.com/apache/flink/pull/2158#discussion_r70246597
--- Diff: docs/apis/metrics.md ---
@@ -0,0 +1,441 @@
+---
+title: "Metrics"
+# Top-level navigation
+top-nav-group: apis
+top-nav-pos: 13
+top-nav-title: "Metrics"
+---
+<!--
+Licensed to the Apache Software Foundation (ASF) under one
+or more contributor license agreements. See the NOTICE file
+distributed with this work for additional information
+regarding copyright ownership. The ASF licenses this file
+to you under the Apache License, Version 2.0 (the
+"License"); you may not use this file except in compliance
+with the License. You may obtain a copy of the License at
+
+ http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing,
+software distributed under the License is distributed on an
+"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+KIND, either express or implied. See the License for the
+specific language governing permissions and limitations
+under the License.
+-->
+
+Flink exposes a metric system that allows gathering and exposing metrics
to external systems.
+
+* This will be replaced by the TOC
+{:toc}
+
+## 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) {
+ this.counter = getRuntimeContext()
+ .getMetricGroup()
+ .counter("myCounter");
+ }
+
+ @public Integer map(String value) throws Exception {
+ this.counter.inc();
+ }
+}
+
+{% endhighlight %}
+
+Alternatively you can also use your own `Counter` implementation:
+
+{% highlight java %}
+
+public class MyMapper extends RichMapFunction<String, Integer> {
+ private Counter counter;
+
+ @Override
+ public void open(Configuration config) {
+ 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 no 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) {
+ getRuntimeContext()
+ .getMetricGroup()
+ .gauge("MyGauge", new Gauge<Integer>() {
+ @Override
+ public Integer getValue() {
+ return valueToExpose;
+ }
+ });
+ }
+}
+
+{% endhighlight %}
+
+Note that reporters will turn the exposed object into a `String`, which
means that a meaningful `toString()` implementation is required.
+
+#### Histogram
+
+A `Histogram` measures 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) {
+ this.histogram = getRuntimeContext()
+ .getMetricGroup()
+ .histogram("myHistogram", new MyHistogram());
+ }
+
+ @public Integer map(Long value) throws Exception {
+ this.histogram.update(value);
+ }
+}
+{% endhighlight %}
+
+Flink does not provide a default implementation for `Histogram`, but
offers a {% gh_link
flink-metrics/flink-metrics-dropwizard/src/main/java/org/apache/flink/dropwizard/metrics/DropwizardHistogramWrapper.java
"Wrapper" %} that allows usage of Codahale/DropWizard histograms.
+To use this wrapper add the following dependency in your `pom.xml`:
+{% highlight xml %}
+<dependency>
+ <groupId>org.apache.flink</groupId>
+ <artifactId>flink-metrics-dropwizard</artifactId>
+ <version>{{site.version}}</version>
+</dependency>
+{% endhighlight %}
+
+You can then register a Codahale/DropWizard histogram like this:
+
+{% highlight java %}
+public class MyMapper extends RichMapFunction<Long, Integer> {
+ private Histogram histogram;
+
+ @Override
+ public void open(Configuration config) {
+ com.codahale.metrics.Histogram histogram =
+ new com.codahale.metrics.Histogram(new SlidingWindowReservoir(500));
+
+ this.histogram = getRuntimeContext()
+ .getMetricGroup()
+ .histogram("myHistogram", new DropWizardHistogramWrapper(histogram));
+ }
+}
+{% endhighlight %}
+
+## Scope
+
+Every metric is assigned an identifier under which it will be reported
that is based on 3 components: the user-provided name when registering the
metric, an optional user-defined scope and a system-provided scope.
+For example, if `A.B` is the sytem scope, `C.D` the user scope and `E` the
name, then the identifier for the metric will be `A.B.C.D.E`.
+
+### User Scope
+
+You can define a user scope by calling either `MetricGroup#addGroup(String
name)` or `MetricGroup#addGroup(int name)`.
+
+{% highlight java %}
+
+counter = getRuntimeContext()
+ .getMetricGroup()
+ .addGroup("MyMetrics")
+ .counter("myCounter");
+
+{% endhighlight %}
+
+### System Scope
+
+The system scope contains context information about the metric, for
example in which task it was registered or what job that task belongs to.
+
+Which context information should be included can be configured by setting
the following keys in `conf/flink-conf.yaml`.
+Each of these keys expect a format string that may contain constants (e.g.
"taskmanager") and variables (e.g. "<task_id>") which will be replaced at
runtime.
+
+- `metrics.scope.jm`
+ - Default: <host>.jobmanager
+ - Applied to all metrics that were scoped to a job manager.
+- `metrics.scope.jm.job`
+ - Default: <host>.jobmanager.<job_name>
+ - Applied to all metrics that were scoped to a job manager and job.
+- `metrics.scope.tm`
+ - Default: <host>.taskmanager.<tm_id>
+ - Applied to all metrics that were scoped to a task manager.
+- `metrics.scope.tm.job`
+ - Default: <host>.taskmanager.<tm_id>.<job_name>
+ - Applied to all metrics that were scoped to a task manager and job.
+- `metrics.scope.tm.task`
+ - Default:
<host>.taskmanager.<tm_id>.<job_name>.<task_name>.<subtask_index>
+ - Applied to all metrics that were scoped to a task.
+- `metrics.scope.tm.operator`
+ - Default:
<host>.taskmanager.<tm_id>.<job_name>.<operator_name>.<subtask_index>
+ - Applied to all metrics that were scoped to an operator.
+
+There are no restrictions on the number or order of variables. Variables
are case sensitive.
+
+The default scope for operator metrics will result in an identifier akin
to `localhost.taskmanager.1234.MyJob.MyOperator.0.MyMetric`
+
+If you also want to include the task name but omit the task manager
information you can specify the following format:
+
+`metrics.scope.tm.operator:
<host>.<job_name>.<task_name>.<operator_name>.<subtask_index>`
+
+This could create the identifier
`localhost.MyJob.MySource_->_MyOperator.MyOperator.0.MyMetric`.
+
+Note that for this format string an identifier clash can occur should the
same job be run multiple times concurrently, which can lead to inconsistent
metric data.
+As such it is advised to either use format strings that provide a certain
degree of uniqueness by including IDs (e.g <job_id>)
+or by assigning unique names to jobs and operators.
+
+### List of all Variables
+
+- JobManager: <host>
+- TaskManager: <host>, <tm_id>
+- Job: <job_id>, <job_name>
+- Task: <task_id>, <task_name>, <task_attempt_id>,
<task_attempt_num>, <subtask_index>
+- Operator: <operator_name>, <subtask_index>
+
+## Reporter
+
+Metrics can be exposed to an external system by configuring a reporter in
`conf/flink-conf.yaml`.
+
+- `metrics.reporter.class`: The class of the reporter to use.
+ - Example: org.apache.flink.metrics.reporter.JMXReporter
+- `metrics.reporter.arguments`: A list of named parameters that are passed
to the reporter.
+ - Example: --host localhost --port 9010
+- `metrics.reporter.interval`: The interval between reports.
+ - Example: 10 SECONDS
+
+You can write your own `Reporter` by implementing the
`org.apache.flink.metrics.reporter.MetricReporter` interface.
+If the Reporter should send out reports regularly you have to implement
the `Scheduled` interface as well.
+
+By default Flink uses JMX to expose metrics.
+All non-JMXReporters are not part of the distribution. To use them you
have to copy the respective fat jar to the `/lib` folder.
+
+The following sections list the supported reporters.
+
+### JMX
+
+The port for JMX can be configured by setting the `metrics.jmx.port` key.
This parameter expects either a single port
+or a port range, with the default being 9010-9025. The used port is shown
in the relevant job or task manager log.
+
+### Ganglia (org.apache.flink.metrics.ganglia.GangliaReporter)
+Dependency:
+{% highlight xml %}
+<dependency>
+ <groupId>org.apache.flink</groupId>
+ <artifactId>flink-metrics-ganglia</artifactId>
+ <version>{{site.version}}</version>
+</dependency>
+{% endhighlight %}
+
+Parameters:
+
+- `host` - the ganglia server host
--- End diff --
The `udp_recv_channel.bind` is set per default in the `gmond.conf` if you
set up Ganglia.
---
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.
---
