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https://issues.apache.org/jira/browse/KAFKA-6819?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16722619#comment-16722619
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Guozhang Wang commented on KAFKA-6819:
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Please see my other comment on KAFKA-6820.
> Refactor build-in StreamsMetrics internal implementations
> ---------------------------------------------------------
>
> Key: KAFKA-6819
> URL: https://issues.apache.org/jira/browse/KAFKA-6819
> Project: Kafka
> Issue Type: Improvement
> Components: streams
> Reporter: Guozhang Wang
> Priority: Major
>
> Our current internal implementations of StreamsMetrics and different layered
> metrics like StreamMetricsThreadImpl, TaskMetrics, NodeMetrics etc are a bit
> messy nowadays. We could improve on the current situation by doing the
> following:
> 0. For thread-level metrics, refactor the {{StreamsMetricsThreadImpl}} class
> to {{ThreadMetrics}} such that a) it does not extend from
> {{StreamsMetricsImpl}} but just include the {{StreamsMetricsThreadImpl}} as
> its constructor parameters. And make its constructor, replacing with a static
> {{addAllSensors(threadName)}} that tries to register all the thread-level
> sensors for the given thread name.
> 1. Add a static function for each of the built-in sensors of the thread-level
> metrics in {{ThreadMetrics}} that relies on the internal
> {{StreamsMetricsConventions}} to get thread level sensor names. If the sensor
> cannot be found from the internal {{Metrics}} registry, create the sensor
> on-the-fly.
> 2.a Add a static {{removeAllSensors(threadName)}} function in
> {{ThreadMetrics}} that tries to de-register all the thread-level metrics for
> this thread, if there is no sensors then it will be a no-op. In
> {{StreamThread#close()}} we will trigger this function; and similarly in
> `TopologyTestDriver` when we close the driver we will also call this function
> as well. As a result, the {{ThreadMetrics}} class itself would only contain
> static functions with no member fields at all.
> 2.b We can consider doing the same for {{TaskMetrics}}, {{NodeMetrics}} and
> {{NamedCacheMetrics}} as well, and add a {{StoreMetrics}} following the
> similar pattern: although these metrics are not accessed externally to their
> enclosing class in the future this may be changed as well.
> 3. Then, we only pass {{StreamsMetricsImpl}} around between the internal
> classes, to access the specific sensor whenever trying to record it.
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