MaxGekk commented on issue #26134: [SPARK-29486][SQL] CalendarInterval should 
have 3 fields: months, days and microseconds
URL: https://github.com/apache/spark/pull/26134#issuecomment-542793129
 
 
   > @MaxGekk do you think Spark violates the SQL standard if ZoneId is used to 
represent the session local timezone?
   
   @cloud-fan I think so. If we accept the session time zone as zone offset 
(`TIMEZONE_HOUR:TIMEZONE_MINUTE`) only some problems will gone for sure. And 
this will speed up date-time operations significantly because conversion of 
`ZoneId` -> `ZoneOffset` is very time consuming. It has to look up at 
historical rules, for instance: 
http://hg.openjdk.java.net/jdk8/jdk8/jdk/file/687fd7c7986d/src/share/classes/java/time/zone/ZoneRules.java#l633
   
   > I see many datetime operations in DateTimeUtils are using ZoneId.
   
   ZoneId itself is not the problem because ZoneOffset is sub-type of ZoneId 
and Java 8 time functions can optimally handle ZoneId instances when they are 
ZoneOffset actually. Theoretically, we could require 
`spark.sql.session.timeZone` to be set as zone offset 
`TIMEZONE_HOUR:TIMEZONE_MINUTE` but this will break user apps highly likely.

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