[FLINK-12325] Statsd reporter gives wrong metrics when using negative numbers

• Type: Bug
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: 1.6.4, 1.7.2, 1.8.0
• Fix Version/s: 1.9.0
• Component/s: Runtime / Metrics
• Labels: pull-request-available
• Assignee: Richard Deurwaarder
• Reporter: Richard Deurwaarder
• Created: 24/Apr/19 18:18
• Updated: 09/May/19 07:01
• Resolved: 09/May/19 07:01

Description

The statsd reporter has a bug I believe when using negative numbers.

 

This is because when a metric is sent it is first converted to a string value. This means 100 becomes "100" and -100 becomes "-100". This value is then sent to statsd as a gauge value.

See this line for the conversion to string: https://github.com/apache/flink/blob/master/flink-metrics/flink-metrics-statsd/src/main/java/org/apache/flink/metrics/statsd/StatsDReporter.java#L130

And this line for sending it as a gauge:

https://github.com/apache/flink/blob/master/flink-metrics/flink-metrics-statsd/src/main/java/org/apache/flink/metrics/statsd/StatsDReporter.java#L184

 

This means a value of -100 will be sent like this:

<metric_name>:-100|g

 

The statsd protocol how ever states the following (https://github.com/statsd/statsd/blob/master/docs/metric_types.md#gauges):

Adding a sign to the gauge value will change the value, rather than setting it.

 

 

So sending -100 multiple times means the gauge in statsd will be decremented multiple times, rather than set to -100.

 

I believe this isn't how flink expects it to work, is it?

Issue Links

• links to: GitHub Pull Request #8259