0lai0 commented on code in PR #5216:
URL: https://github.com/apache/datafusion-comet/pull/5216#discussion_r3740961790
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spark/src/main/scala/org/apache/spark/sql/comet/DecimalPrecision.scala:
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@@ -40,6 +40,24 @@ import org.apache.spark.sql.types.DecimalType
*/
object DecimalPrecision {
def promote(expr: Expression): Expression = {
+ // `transformUp` walks and rebuilds every node even when no case matches,
and the serde calls
+ // this once per expression it converts, so skip it when there is nothing
to rewrite.
Review Comment:
Nit: Could you reword this comment slightly?
`transformUp` does call mapChildren at every node, but specialized
mapChildren (UnaryLike / BinaryLike / etc.) skip the copy via fastEquals when
nothing changed , so it doesn't really "rebuild every node".
The cost is the traversal + allocations (`children.map` /
`mapProductIterator`).
The PR body's wording already captures this well; matching that here would
help future profilers.
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