[SPARK-13100][SQL] improving the performance of stringToDate method in DateTimeUtils.scala

 In jdk1.7 TimeZone.getTimeZone() is synchronized, so use an instance variable to hold an GMT TimeZone object instead of instantiate it every time.

Author: wangyang <wangyang@haizhi.com>

Closes #10994 from wangyang1992/datetimeUtil.

1 files changed, 2 insertions, 1 deletions

diff --git a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/util/DateTimeUtils.scala b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/util/DateTimeUtils.scala
index f18c052b68..a159bc6a61 100644
--- a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/util/DateTimeUtils.scala
+++ b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/util/DateTimeUtils.scala
@@ -55,6 +55,7 @@ object DateTimeUtils {
   // this is year -17999, calculation: 50 * daysIn400Year
   final val YearZero = -17999
   final val toYearZero = to2001 + 7304850
+  final val TimeZoneGMT = TimeZone.getTimeZone("GMT")
 
   @transient lazy val defaultTimeZone = TimeZone.getDefault
 
@@ -407,7 +408,7 @@ object DateTimeUtils {
         segments(2) < 1 || segments(2) > 31) {
       return None
     }
-    val c = Calendar.getInstance(TimeZone.getTimeZone("GMT"))
+    val c = Calendar.getInstance(TimeZoneGMT)
     c.set(segments(0), segments(1) - 1, segments(2), 0, 0, 0)
     c.set(Calendar.MILLISECOND, 0)
     Some((c.getTimeInMillis / MILLIS_PER_DAY).toInt)