j-esse commented on a change in pull request #23556: [SPARK-26626][SQL] Maximum
size for repeatedly substituted aliases in SQL expressions
URL: https://github.com/apache/spark/pull/23556#discussion_r268004507
##########
File path:
sql/catalyst/src/main/scala/org/apache/spark/sql/internal/SQLConf.scala
##########
@@ -1717,6 +1717,15 @@ object SQLConf {
"and java.sql.Date are used for the same purpose.")
.booleanConf
.createWithDefault(false)
+
+ val MAX_REPEATED_ALIAS_SIZE =
+ buildConf("spark.sql.maxRepeatedAliasSize")
+ .internal()
+ .doc("The maximum size of alias expression that will be substituted
multiple times " +
+ "(size defined by the number of nodes in the expression tree). " +
+ "Used by the CollapseProject optimizer, and PhysicalOperation.")
+ .intConf
+ .createWithDefault(100)
Review comment:
@HyukjinKwon increasing the driver memory unfortunately isn't an option,
because due to the exponential tree size explosion, the necessary memory would
be much larger than that available on most servers. Also, users wouldn't know
that they needed a very large driver memory size, because they can be running
small queries over small data.
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