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https://issues.apache.org/jira/browse/SPARK-34806?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17383394#comment-17383394
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Apache Spark commented on SPARK-34806:
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User 'EnricoMi' has created a pull request for this issue:
https://github.com/apache/spark/pull/33422
> Helper class for batch Dataset.observe()
> ----------------------------------------
>
> Key: SPARK-34806
> URL: https://issues.apache.org/jira/browse/SPARK-34806
> Project: Spark
> Issue Type: New Feature
> Components: SQL
> Affects Versions: 3.2.0
> Reporter: Enrico Minack
> Assignee: Enrico Minack
> Priority: Minor
> Fix For: 3.3.0
>
>
> The {{observe}} method has been added to the {{Dataset}} API in 3.0.0. It
> allows to collect aggregate metrics over data of a Dataset while they are
> being processed during an action.
> These metrics are collected in a separate thread after registering
> {{QueryExecutionListener}} for batch datasets and {{StreamingQueryListener}}
> for stream datasets, respectively. While in streaming context it makes
> perfectly sense to process incremental metrics in an event-based fashion, for
> simple batch datatset processing, a single result should be retrievable
> without the need to register listeners or handling threading.
> Introducing an {{Observation}} helper class can hide that complexity for
> simple use-cases in batch processing.
> Similar to {{AccumulatorV2}} provided by {{SparkContext}} (e.g.
> {{SparkContext.LongAccumulator}}), the {{SparkSession}} can provide a method
> to create a new {{Observation}} instance and register it with the session.
> Alternatively, an {{Observation}} instance could be instantiated on its own
> which on calling {{Observation.on(Dataset)}} registers with
> {{Dataset.sparkSession}}. This "registration" registers a listener with the
> session that retrieves the metrics.
> The {{Observation}} class provides methods to retrieve the metrics. This
> retrieval has to wait for the listener to be called in a separate thread. So
> all methods will wait for this, optionally with a timeout:
> - {{Observation.get}} waits without timeout and returns the metric.
> - {{Observation.option(time, unit)}} waits at most {{time}}, returns the
> metric as an {{Option}}, or {{None}} when the timeout occurs.
> - {{Observation.waitCompleted(time, unit)}} waits for the metrics and
> indicates timeout by returning {{false}}.
> Obviously, an action has to be called on the observed dataset before any of
> these methods are called, otherwise a timeout will occur.
> With {{Observation.reset}}, another action can be observed. Finally,
> {{Observation.close}} unregisters the listener from the session.
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