maropu commented on a change in pull request #23635: [SPARK-26709][SQL]
OptimizeMetadataOnlyQuery does not handle empty records correctly
URL: https://github.com/apache/spark/pull/23635#discussion_r250566874
##########
File path:
sql/catalyst/src/main/scala/org/apache/spark/sql/internal/SQLConf.scala
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@@ -585,9 +585,10 @@ object SQLConf {
.doc("When true, enable the metadata-only query optimization that use the
table's metadata " +
"to produce the partition columns instead of table scans. It applies
when all the columns " +
"scanned are partition columns and the query has an aggregate operator
that satisfies " +
- "distinct semantics.")
+ "distinct semantics. By default the optimization is disabled, since it
may return " +
+ "incorrect results with empty tables.")
.booleanConf
- .createWithDefault(true)
+ .createWithDefault(false)
Review comment:
How about making this conf. internal and always printing a warning message
when this flag enabled and the rule applied?
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