feat: support NullType in row-to-Arrow conversion and shuffle#4460
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kazuyukitanimura
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May 28, 2026
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Does it make sense to create a sql test file for LocalTableScanExec ?
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| test("CometLocalTableScanExec handles NullType column") { | ||
| withSQLConf(CometConf.COMET_EXEC_LOCAL_TABLE_SCAN_ENABLED.key -> "true") { | ||
| val df = spark.sql("SELECT * FROM VALUES ('a', null), ('b', null) AS t(x, y)") |
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Just making sure whether constant folding optimization is not affecting anything here....?
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I manually inspected the plans, but the native shuffle suite is a more exhaustive check since it sees that we shuffled the data.
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Thanks for the review @kazuyukitanimura!
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Which issue does this PR close?
Closes #4457.
Rationale for this change
NullTypecolumns currently break Comet at the row-to-Arrow boundary.Utils.toArrowTypethrowsUnsupportedOperationExceptionforNullType, which surfaces in two places:CometLocalTableScanExecwhen aLocalTableScancontains aNullTypecolumn (the case in Queries with NullType aggregate fails when native LocalTableScanExec is enabled #4457, e.g.SELECT max(col) FROM VALUES (NULL), (NULL) AS t(col)).CometShuffleExchangeExecwhen a SparkLocalTableScanExecwith aNullTypecolumn feeds a Comet shuffle.NullTypeis well-defined in Arrow (ArrowType.Null) and the SparkArrowWriteralready has aNullWritercase, so the right fix is to support it end-to-end rather than fall back. This PR is an alternative to #4458, which adds aLocalTableScanExec-only fallback and leaves the shuffle path broken.What changes are included in this PR?
Utils.toArrowTypemapsNullTypetoArrowType.Null.CometShuffleExchangeExec.supportedSerializableDataTypeacceptsNullTypefor both native and columnar shuffle.native/shuffle/src/spark_unsafe/row.rs) handlesNullType.How are these changes tested?
New regression tests:
CometExecSuite "CometLocalTableScanExec handles NullType nested in struct/array/map"coversNullTypenested underStructType,ArrayType, andMapTypethroughCometLocalTableScanExec.CometColumnarShuffleSuite "columnar shuffle with NullType passthrough column"covers JVM-input columnar shuffle with aNullTypecolumn. Replaces the older"Fallback to Spark for unsupported input besides ordering"test, which asserted the previous fallback behavior.CometNativeShuffleSuite "native shuffle with NullType passthrough column"covers native shuffle with a CometLocalTableScansource containing aNullTypecolumn. Gated onspark.comet.exec.localTableScan.enabled=truebecause native shuffle requires Comet input.