[jira] [Assigned] (FLINK-40295) Document UDF metrics

["Weiqing Yang (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/FLINK-40295?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Weiqing Yang reassigned FLINK-40295:
------------------------------------

    Assignee: Weiqing Yang

> Document UDF metrics
> --------------------
>
>                 Key: FLINK-40295
>                 URL: https://issues.apache.org/jira/browse/FLINK-40295
>             Project: Flink
>          Issue Type: Sub-task
>          Components: Documentation
>            Reporter: Weiqing Yang
>            Assignee: Weiqing Yang
>            Priority: Major
>              Labels: pull-request-available
>
> This is the fourth of four sub-tasks implementing FLIP-485.
> FLIP: https://cwiki.apache.org/confluence/spaces/FLINK/pages/373885706/FLIP-485+Add+UDF+Metrics
> Vote thread: https://lists.apache.org/thread/symqpswsohl2s5wmtkcw0jjp1w5dot0n
> Document the UDF metrics feature in docs/content/docs/ops/metrics.md and its Chinese counterpart.
> Two additions:
> * A UDF section in the metrics reference listing {{udfProcessingTime}} and {{udfExceptionCount}}, their types, and their operator-scoped naming, where the full identifier is {{<operator_name>.udf.<udf_name>.<metric>}}.
> * A "UDF metrics" section alongside the existing state-access-latency section, covering how to enable the feature with {{table.exec.udf-metric-enabled}}, how {{table.exec.udf-metric.sample-interval}} trades accuracy against overhead, the fact that exceptions are counted on every invocation rather than sampled, which function kinds are covered, and the recommendation to use the metrics for debugging.
> The overhead wording notes that because only the sampled invocations are timed, the remaining invocations cost a single counter increment, so the default interval keeps the overhead of the enabled path small. This answers a question raised on the reference implementation about the cost of the feature when it is switched on.
> Not covered, and stated as such in the docs: process table functions (PROCESS_TABLE), aggregate functions, and functions registered through the deprecated registerFunction API.



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