Github user cloud-fan commented on a diff in the pull request:
https://github.com/apache/spark/pull/7392#discussion_r34661517
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/codegen/GenerateOrdering.scala
---
@@ -46,30 +46,47 @@ object GenerateOrdering extends
CodeGenerator[Seq[SortOrder], Ordering[InternalR
protected def create(ordering: Seq[SortOrder]): Ordering[InternalRow] = {
val ctx = newCodeGenContext()
- val comparisons = ordering.zipWithIndex.map { case (order, i) =>
--- End diff --
In interpreted mode, we use the same expression to eval 2
[rows](https://github.com/apache/spark/blob/master/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/rows.scala#L164-L165),
which means we only keep one copy of mutable states for that expression.
However, in `GenerateOrdering`, we call `order.child.gen(ctx)` twice and thus
make 2 copy of mutable states for that expression. This is inconsistent, and
may return different compare result.
However, should we allow stateful expressions in order by?
cc @davies @rxin
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