[jira] [Created] (SPARK-42205) Remove logging of Accumulables in Task/Stage start events in JsonProtocol

["Josh Rosen (Jira)" <ji...@apache.org>]

Josh Rosen created SPARK-42205:
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             Summary: Remove logging of Accumulables in Task/Stage start events in JsonProtocol
                 Key: SPARK-42205
                 URL: https://issues.apache.org/jira/browse/SPARK-42205
             Project: Spark
          Issue Type: Improvement
          Components: Spark Core
    Affects Versions: 3.0.0
            Reporter: Josh Rosen


Spark's JsonProtocol event logs (used by the history server) are impacted by a race condition when tasks / stages finish very quickly:

The SparkListenerTaskStart and SparkListenerStageSubmitted events contain mutable TaskInfo and StageInfo objects, which in turn contain Accumulables fields. When a task or stage is submitted, Accumulables is initially empty. When the task or stage finishes, this field is updated with values from the task.

If a task or stage finishes before the start event has been logged by the event logging listener then the _start_ event will contain the Accumulable values from the task or stage _end_ event. 

This information isn't used by the History Server and contributes to wasteful bloat in event log sizes. In one real-world log, I found that ~10% of the uncompressed log size was due to these redundant Accumulable fields.

I propose that we update JsonProtocol to skip the logging of this field for Start/Submitted events. 



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