Github user mallman commented on a diff in the pull request:
https://github.com/apache/spark/pull/16578#discussion_r151026919
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/internal/SQLConf.scala ---
@@ -961,6 +961,15 @@ object SQLConf {
.booleanConf
.createWithDefault(true)
+ val NESTED_SCHEMA_PRUNING_ENABLED =
+ buildConf("spark.sql.nestedSchemaPruning.enabled")
+ .internal()
+ .doc("Prune nested fields from a logical relation's output which are
unnecessary in " +
+ "satisfying a query. This optimization allows columnar file format
readers to avoid " +
+ "reading unnecessary nested column data.")
+ .booleanConf
+ .createWithDefault(true)
--- End diff --
Giving it more though, I believe it's prudent to choose correctness over
performance. I will change the default to `false`. "Power users" will set it to
`true` and (hopefully) report a problem if they run into one.
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