Github user ssonker commented on a diff in the pull request:
https://github.com/apache/spark/pull/21505#discussion_r194305723
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/util/DateTimeUtils.scala
---
@@ -111,6 +113,23 @@ object DateTimeUtils {
computedTimeZones.computeIfAbsent(timeZoneId, computeTimeZone)
}
+ private val threadLocalComputedCalendarsMap =
+ new ThreadLocal[mutable.Map[TimeZone, Calendar]] {
--- End diff --
@kiszk @viirya I've tried running benchmarks for with/without
```mutable.Map``` implementation. Looks like setting timezone in a calendar
instance is a costly operation and it drags the performance down. As the number
of timezones cannot be large, maintaining a map will not be a huge memory
overhead. So, I suggest going with the ```mutable.Map``` approach. Comments?
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