dongjoon-hyun commented on a change in pull request #29950:
URL: https://github.com/apache/spark/pull/29950#discussion_r502311982
##########
File path:
sql/catalyst/src/main/scala/org/apache/spark/sql/internal/SQLConf.scala
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@@ -1926,6 +1926,19 @@ object SQLConf {
.booleanConf
.createWithDefault(true)
+ val MAX_COMMON_EXPRS_IN_COLLAPSE_PROJECT =
+ buildConf("spark.sql.optimizer.maxCommonExprsInCollapseProject")
+ .doc("An integer number indicates the maximum allowed number of a common
expression " +
+ "can be collapsed into upper Project from lower Project by optimizer
rule " +
+ "`CollapseProject`. Normally `CollapseProject` will collapse adjacent
Project " +
+ "and merge expressions. But in some edge cases, expensive expressions
might be " +
+ "duplicated many times in merged Project by this optimization. This
config sets " +
+ "a maximum number. Once an expression is duplicated more than this
number " +
+ "if merging two Project, Spark SQL will skip the merging.")
+ .version("3.1.0")
+ .intConf
+ .createWithDefault(20)
Review comment:
Just a question. Is there a reason to choose `20`?
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