VindhyaG opened a new pull request, #59589: URL: https://github.com/apache/spark/pull/59589
Broadcast hash join fails with "Subquery has not finished" when the join key contains an uncorrelated scalar subquery. Rootcause provided bu the the reporter : ExtractEquiJoinKeys accepts a join key containing an uncorrelated scalar subquery (it has no references, so canEvaluate passes for either side), and the key lands in HashedRelationBroadcastMode(key: Seq[Expression]). Scalar subqueries are normally started and awaited by SparkPlan.prepareSubqueries and waitForSubqueries, which discover them through QueryPlan.expressions. That walk only surfaces Expression, Option and Iterable constructor arguments ([src](https://github.com/apache/spark/blob/4dcdd4dba544210898180a410b8b30e0b85157cb/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/plans/QueryPlan.scala#L327-L341)). BroadcastMode is an opaque case class, so the subquery inside mode.key is never registered or awaited on the exchange node. The broadcast thread then evaluates/code-generates the un-updated execution.ScalarSubquery and hits the require(updated) guard ([src](https://github.com/apache/spark/blob/4dcdd4dba544210898180a410b8b30e0b85157cb/sql/core/src/main/scala/org/apache/spark/sql/execution/subquery.scala#L99)). The join node's own waitForSubqueries does see its leftKeys/rightKeys, but has no happens-before relationship with the broadcast thread, which doPrepare launches eagerly. ### What changes were proposed in this pull request? <!-- Please clarify what changes you are proposing. The purpose of this section is to outline the changes and how this PR fixes the issue. If possible, please consider writing useful notes for better and faster reviews in your PR. See the examples below. 1. If you refactor some codes with changing classes, showing the class hierarchy will help reviewers. 2. If you fix some SQL features, you can provide some references of other DBMSes. 3. If there is design documentation, please add the link. 4. If there is a discussion in the mailing list, please add the link. --> Register the HashedRelationBroadcastMode key and wait for the subqueries to be finished before triggering transform. Since, registering the key to the expressions was the most simple with least changes in the architecture went with that solution out of all the solutions suggested. ### Why are the changes needed? <!-- Please clarify why the changes are needed. For instance, 1. If you propose a new API, clarify the use case for a new API. 2. If you fix a bug, you can clarify why it is a bug. --> ### Does this PR introduce _any_ user-facing change? <!-- Note that it means *any* user-facing change including all aspects such as new features, bug fixes, or other behavior changes. Documentation-only updates are not considered user-facing changes. If yes, please clarify the previous behavior and the change this PR proposes - provide the console output, description and/or an example to show the behavior difference if possible. If possible, please also clarify if this is a user-facing change compared to the released Spark versions or within the unreleased branches such as master. If no, write 'No'. --> No ### How was this patch tested? <!-- If tests were added, say they were added here. Please make sure to add some test cases that check the changes thoroughly including negative and positive cases if possible. If it was tested in a way different from regular unit tests, please clarify how you tested step by step, ideally copy and paste-able, so that other reviewers can test and check, and descendants can verify in the future. If tests were not added, please describe why they were not added and/or why it was difficult to add. If benchmark tests were added, please run the benchmarks in GitHub Actions for the consistent environment, and the instructions could accord to: https://spark.apache.org/developer-tools.html#github-workflow-benchmarks. --> Tested the changes locally with the code provided in the bug and UT. ### Was this patch authored or co-authored using generative AI tooling? <!-- If generative AI tooling has been used in the process of authoring this patch, please include the phrase: 'Generated-by: ' followed by the name of the tool and its version. If no, write 'No'. Please refer to the [ASF Generative Tooling Guidance](https://www.apache.org/legal/generative-tooling.html) for details. --> Generated-by: GPT 5.5 -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected] --------------------------------------------------------------------- To unsubscribe, e-mail: [email protected] For additional commands, e-mail: [email protected]
