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https://issues.apache.org/jira/browse/FLINK-5095?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Bowen Li reassigned FLINK-5095:
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Assignee: Bowen Li
> Add explicit notifyOfAddedX methods to MetricReporter interface
> ---------------------------------------------------------------
>
> Key: FLINK-5095
> URL: https://issues.apache.org/jira/browse/FLINK-5095
> Project: Flink
> Issue Type: Improvement
> Components: Metrics
> Affects Versions: 1.1.3
> Reporter: Chesnay Schepler
> Assignee: Bowen Li
> Priority: Minor
>
> I would like to start a discussion on the MetricReporter interface,
> specifically the methods that notify a reporter of added or removed metrics.
> Currently, the methods are defined as follows:
> {code}
> void notifyOfAddedMetric(Metric metric, String metricName, MetricGroup group);
> void notifyOfRemovedMetric(Metric metric, String metricName, MetricGroup
> group);
> {code}
> All metrics, regardless of their actual type, are passed to the reporter with
> these methods.
> Since the different metric types have to be handled differently we thus force
> every reporter to do something like this:
> {code}
> if (metric instanceof Counter) {
> Counter c = (Counter) metric;
> // deal with counter
> } else if (metric instanceof Gauge) {
> // deal with gauge
> } else if (metric instanceof Histogram) {
> // deal with histogram
> } else if (metric instanceof Meter) {
> // deal with meter
> } else {
> // log something or throw an exception
> }
> {code}
> This has a few issues
> * the instanceof checks and castings are unnecessary overhead
> * it requires the implementer to be aware of every metric type
> * it encourages throwing an exception in the final else block
> We could remedy all of these by reworking the interface to contain explicit
> add/remove methods for every metric type. This would however be a breaking
> change and blow up the interface to 12 methods from the current 4. We could
> also add a RichMetricReporter interface with these methods, which would
> require relatively little changes but add additional complexity.
> I was wondering what other people think about this.
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