beliefer commented on pull request #26875:
URL: https://github.com/apache/spark/pull/26875#issuecomment-647877651
@ulysses-you I'm sorry! I lost some thing.
---- test 1 ----
```
val df1 = spark.range(0, 20000, 1, 200).selectExpr("uuid() as c1")
val df2 = spark.range(0, 20000, 1, 200).selectExpr("uuid() as c2")
val start = System.currentTimeMillis
df1.join(df2).where("c2 like c1").count()
// 3 times test
// before 159228, 157541, 157721
// after 14378, 11545, 11498
println(System.currentTimeMillis - start)
```
---- test3 ----
```
val df1 = spark.range(0, 20000, 1, 200).selectExpr("uuid() as c1")
val df2 = spark.range(0, 20000, 1, 200).selectExpr("uuid() as c2")
val start = System.currentTimeMillis
df1.join(df2).where("c1 like c2").count()
// 3 times test
// before 159226, 159147, 159587
// after 159641, 160960, 160091
println(System.currentTimeMillis - start)
```
Why is test1 and test3 so different in time?
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