Github user cloud-fan commented on a diff in the pull request: https://github.com/apache/spark/pull/20024#discussion_r159574368 --- Diff: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/Cast.scala --- @@ -608,6 +723,22 @@ case class Cast(child: Expression, dataType: DataType, timeZoneId: Option[String val tz = ctx.addReferenceObj("timeZone", timeZone) (c, evPrim, evNull) => s"""$evPrim = UTF8String.fromString( org.apache.spark.sql.catalyst.util.DateTimeUtils.timestampToString($c, $tz));""" + case ar: ArrayType => + val bufferClass = classOf[StringBuffer].getName + val buffer = ctx.addMutableState(bufferClass, "buffer", v => s"$v = new $bufferClass();") --- End diff -- We are casting array to string, which is expected to be slow. We don't need to save the object creation by introducing this mutable state. We can always create a new one.
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