Github user wzhfy commented on a diff in the pull request:
https://github.com/apache/spark/pull/17286#discussion_r106602975
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/internal/SQLConf.scala ---
@@ -710,6 +710,14 @@ object SQLConf {
.intConf
.createWithDefault(12)
+ val JOIN_REORDER_CARD_WEIGHT =
+ buildConf("spark.sql.cbo.joinReorder.card.weight")
+ .doc("The weight of cardinality (number of rows) for plan cost
comparison in join reorder: " +
+ "rows * weight + size * (1 - weight).")
+ .doubleConf
+ .checkValue(weight => weight >= 0 && weight <= 1, "The weight value
must be in [0, 1].")
+ .createWithDefault(0.7)
--- End diff --
`0.7` is just an empirical value, I think it's better to be able to tune
it. Maybe mark it internal?
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