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https://issues.apache.org/jira/browse/SPARK-32862?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Jungtaek Lim resolved SPARK-32862.
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Fix Version/s: 3.1.0
Resolution: Fixed
Issue resolved by pull request 30076
[https://github.com/apache/spark/pull/30076]
> Left semi stream-stream join
> ----------------------------
>
> Key: SPARK-32862
> URL: https://issues.apache.org/jira/browse/SPARK-32862
> Project: Spark
> Issue Type: Sub-task
> Components: Structured Streaming
> Affects Versions: 3.1.0
> Reporter: Cheng Su
> Assignee: Cheng Su
> Priority: Major
> Fix For: 3.1.0
>
>
> Current stream-stream join supports inner, left outer and right outer join
> ([https://github.com/apache/spark/blob/master/sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/StreamingSymmetricHashJoinExec.scala#L166]
> ). We do see internally a lot of users are using left semi stream-stream
> join (not spark structured streaming), e.g. I want to get the ad impression
> (join left side) which has click (joint right side), but I don't care how
> many clicks per ad (left semi semantics).
>
> Left semi stream-stream join will work as followed:
> (1).for left side input row, check if there's a match on right side state
> store
> (1.1). if there's a match, output the left side row.
> (1.2). if there's no match, put the row in left side state store (with
> "matched" field to set to false in state store).
> (2).for right side input row, check if there's a match on left side state
> store. If there's a match, update left side row state with "matched" field to
> set to true. Put the right side row in right side state store.
> (3).for left side row needs to be evicted from state store, output the row if
> "matched" field is true.
> (4).for right side row needs to be evicted from state store, doing nothing.
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