advancedxy commented on code in PR #206:
URL:
https://github.com/apache/arrow-datafusion-comet/pull/206#discussion_r1555973542
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spark/src/main/scala/org/apache/comet/CometSparkSessionExtensions.scala:
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@@ -574,18 +580,26 @@ class CometSparkSessionExtensions
}
}
- // CometExec already wraps a `ColumnarToRowExec` for row-based operators.
Therefore,
- // `ColumnarToRowExec` is redundant and can be eliminated.
+ // This rule is responsible for eliminating redundant transitions between
row-based and
+ // columnar-based operators for Comet. Currently, two potential redundant
transitions are:
+ // 1. ColumnarToRowExec at the end of a Spark operator, which is redundant
for Comet operators as
+ // CometExec already wraps a `ColumnarToRowExec` for row-based operators.
+ // 2. Consecutive operators of CometRowToColumnarExec and ColumnarToRowExec,
which might be
+ // possible for Comet to add a `CometRowToColumnarExec` for row-based
operators first, then
+ // Spark only requests row-based output.
Review Comment:
> but the
downstream operator is Spark operator which takes row-based input
hmm, this is another possibility, let me update the comment to include this
one.
The case I described above is that Spark only requests row-based at the end
of the operator, the row-based requirement might be passed down to the
`CometRowToColumnarExec` and then we have a pair of `CometRowToColumnarExec`
and `ColumnarToRowExec`.
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