Ted-Jiang commented on code in PR #2156:
URL: https://github.com/apache/arrow-datafusion/pull/2156#discussion_r845198369


##########
datafusion/physical-expr/src/expressions/in_list.rs:
##########
@@ -32,13 +33,19 @@ use arrow::{
     record_batch::RecordBatch,
 };
 
-use crate::PhysicalExpr;
+use crate::{expressions, PhysicalExpr};
 use arrow::array::*;
 use arrow::buffer::{Buffer, MutableBuffer};
 use datafusion_common::ScalarValue;
 use datafusion_common::{DataFusionError, Result};
 use datafusion_expr::ColumnarValue;
 
+/// Size at which to use a Set rather than Vec for `IN` / `NOT IN`
+/// Value chosen to be consistent with Spark
+/// 
https://github.com/apache/spark/blob/4e95738fdfc334c25f44689ff8c2db5aa7c726f2/sql/catalyst/src/main/scala/org/apache/spark/sql/internal/SQLConf.scala#L259-L265
+/// TODO: add switch codeGen in In_List
+static OPTIMIZER_INSET_THRESHOLD: usize = 10;

Review Comment:
   
![image](https://user-images.githubusercontent.com/37145547/162219787-c7a0941e-72f1-426e-bd03-f86687f8b040.png)
   
   `X`: cost time. `Y`: filter value numbers 
   
   `Blue`: is use List, `orange`: is use Set.  
   
   I did a benchMark in my local, use `select count(*) from orders where 
o_orderkey in (x1, x2, ..., xn)`
   Obviously, Set has a fixed gradient, List cost time increases with the 
parameter number. 
   The intersection of the two lines is located is between 10~20 (same as Spark 
set 10). 
   So, i decided set `OPTIMIZER_INSET_THRESHOLD ` = 10 align with spark.



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