wangyum opened a new pull request, #43617: URL: https://github.com/apache/spark/pull/43617
### What changes were proposed in this pull request? This PR makes `Dataset.isEmpty()` to execute global limit 1 first. `LimitPushDown` may push down global limit 1 to a lower node to improve query performance. Note that we use global limit 1 here, because the local limit cannot be pushed down the group only case: https://github.com/apache/spark/blob/89ca8b6065e9f690a492c778262080741d50d94d/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala#L766-L770 ### Why are the changes needed? Improve query performance. ### Does this PR introduce _any_ user-facing change? No. ### How was this patch tested? Manual testing: ```scala spark.range(300000000).selectExpr("id", "array(id, id % 10, id % 100) as eo").write.saveAsTable("t1") spark.range(100000000).selectExpr("id", "array(id, id % 10, id % 1000) as eo").write.saveAsTable("t2") println(spark.sql("SELECT * FROM t1 LATERAL VIEW explode_outer(eo) AS e UNION SELECT * FROM t2 LATERAL VIEW explode_outer(eo) AS e").isEmpty) ``` Before this PR | After this PR -- | -- <img width="430" alt="image" src="https://github.com/apache/spark/assets/5399861/417adc05-4160-4470-b63c-125faac08c9c";> | <img width="430" alt="image" src="https://github.com/apache/spark/assets/5399861/bdeff231-e725-4c55-9da2-1b4cd59ec8c8";> ### Was this patch authored or co-authored using generative AI tooling? No. -- 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]
