Guozhang Wang created KAFKA-6819:
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Summary: 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
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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