Github user stanzhai commented on the issue:
https://github.com/apache/spark/pull/19301
@viirya
Benchmark code:
```scala
val N = 500L << 22
val benchmark = new Benchmark("agg", N)
val expressions = (0 until 50).map(i => s"sum(id) as r$i")
benchmark.addCase("agg with optimize", numIters = 2) { iter =>
sparkSession.range(N).selectExpr(expressions: _*).collect()
}
benchmark.run()
```
Result:
```
Java HotSpot(TM) 64-Bit Server VM 1.8.0_91-b14 on Mac OS X 10.12.6
Intel(R) Core(TM) i5-4278U CPU @ 2.60GHz
agg: Best/Avg Time(ms) Rate(M/s)
Per Row(ns) Relative
------------------------------------------------------------------------------------------------
agg with optimize 1306 / 1354 1605.7
0.6 1.0X
agg without optimize 121799 / 148115 17.2
58.1 1.0X
```
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