pan3793 commented on code in PR #45155:
URL: https://github.com/apache/spark/pull/45155#discussion_r1499117650
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sql/hive-thriftserver/src/main/scala/org/apache/spark/sql/hive/thriftserver/SparkExecuteStatementOperation.scala:
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@@ -116,7 +116,7 @@ private[hive] class SparkExecuteStatementOperation(
val offset = iter.getPosition
val rows = iter.take(maxRows).toList
Review Comment:
the real matter is `toList` returns a `linked list` that
> Performance
> Time: List has O(1) prepend and head/tail access. Most other operations
are O(n) on the number of elements in the list. This includes the index-based
lookup of elements, length, append and reverse.
The most simplified approach to address the performance issue is
```patch
- val rows = iter.take(maxRows).toList
+ val rows = iter.take(maxRows).IndexedSeq
```
which reduces the time cost of `rows(i)` from O(n) to O(1)
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