[SPARK-59706][SQL] Hoist loop-invariant left row out of the AS-OF join inner scan - #58959
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…n inner scan ### What changes were proposed in this pull request? In `SortMergeAsOfJoinScanner` (`sql/core/src/main/scala/org/apache/spark/sql/execution/joins/SortMergeAsOfJoinExec.scala`), the per-left-row scan over the buffered right group (`findBestBackwardForward` and `findBestForwardNearest`) rebinds both sides of the shared `JoinedRow` on every iteration via `joinedRow.withLeft(leftRow).withRight(rightRow)`. The left row is fixed for the duration of the scan, so this binds `joinedRow.withLeft(leftRow)` once before the loop and keeps only `joinedRow.withRight(rightRow)` inside it. ### Why are the changes needed? The inner scan runs once per buffered right row for every left row, so `withLeft` was called redundantly on each iteration with an argument that never changes within a scan. JFR profiling of `AsOfJoinBenchmark` showed `JoinedRow.withLeft`/`withRight` among the hotter frames in the (interpreted) scanner. Binding the left side once removes the redundant per-row call. This is behavior-preserving: `JoinedRow.withLeft` only stores the left-row reference, nothing mutates the left side within a scan, and `findNext` re-binds both sides before projecting the output row. ### Does this PR introduce _any_ user-facing change? No. ### How was this patch tested? Existing tests pass: `SortMergeAsOfJoinSuite`, `DataFrameAsOfJoinSuite`, `AsOfJoinSQLSuite`, and `AsOfJoinSortMergeSQLSuite` (89 tests). ### Was this patch authored or co-authored using generative AI tooling? Generated-by: Isaac Co-authored-by: Isaac <no-reply@databricks.com>
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This backports #58879 (SPARK-59706) to
branch-4.x. It is a clean cherry-pick of the master commit; the change is identical.What changes were proposed in this pull request?
In
SortMergeAsOfJoinScanner(
sql/core/src/main/scala/org/apache/spark/sql/execution/joins/SortMergeAsOfJoinExec.scala), theper-left-row scan over the buffered right group (
findBestBackwardForwardandfindBestForwardNearest) rebinds both sides of the sharedJoinedRowon every iteration viajoinedRow.withLeft(leftRow).withRight(rightRow). The left row is fixed for the duration of thescan, so this binds
joinedRow.withLeft(leftRow)once before the loop and keeps onlyjoinedRow.withRight(rightRow)inside it.Why are the changes needed?
The inner scan runs once per buffered right row for every left row, so
withLeftwas calledredundantly on each iteration with an argument that never changes within a scan. JFR profiling of
AsOfJoinBenchmarkshowedJoinedRow.withLeft/withRightamong the hotter frames in the(interpreted) scanner. Binding the left side once removes the redundant per-row call. This is
behavior-preserving:
JoinedRow.withLeftonly stores the left-row reference, nothing mutates theleft side within a scan, and
findNextre-binds both sides before projecting the output row.Does this PR introduce any user-facing change?
No.
How was this patch tested?
Backport of #58879 (SPARK-59706); the change is identical to the master PR. Existing AS-OF join
tests cover it (
SortMergeAsOfJoinSuite,DataFrameAsOfJoinSuite,AsOfJoinSQLSuite, andAsOfJoinSortMergeSQLSuite), andbranch-4.xCI runs them.Was this patch authored or co-authored using generative AI tooling?
Generated-by: Isaac
This pull request and its description were written by Isaac.