[jira] [Created] (SPARK-42376) Introduce watermark propagation among operators

["Jungtaek Lim (Jira)" <ji...@apache.org>]

Jungtaek Lim created SPARK-42376:
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             Summary: Introduce watermark propagation among operators
                 Key: SPARK-42376
                 URL: https://issues.apache.org/jira/browse/SPARK-42376
             Project: Spark
          Issue Type: Improvement
          Components: Structured Streaming
    Affects Versions: 3.5.0
            Reporter: Jungtaek Lim


With introduction of SPARK-40925, we enabled workloads containing multiple stateful operators in a single streaming query.

The JIRA ticket clearly described out-of-scope, "Here we propose fixing the late record filtering in stateful operators to allow chaining of stateful operators {*}which do not produce delayed records (like time-interval join or potentially flatMapGroupsWithState){*}".

We identified production use case for stream-stream time-interval join followed by stateful operator (e.g. window aggregation), and propose to address such use case via this ticket.

The design will be described in the PR, but the sketched idea is introducing simulation of watermark propagation among operators. As of now, Spark considers all stateful operators to have same input watermark and output watermark, which introduced the limitation. With this ticket, we construct the logic to simulate watermark propagation so that each operator can have its own (input watermark, output watermark). Operators introducing delayed records will produce delayed output watermark, and downstream operator can take the delay into account as input watermark will be adjusted.



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