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  1. Apache Drill
  2. DRILL-5332

DateVector support uses questionable conversions to a time

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    Details

    • Type: Bug
    • Status: Open
    • Priority: Major
    • Resolution: Unresolved
    • Affects Version/s: 1.9.0
    • Fix Version/s: None
    • Component/s: None
    • Labels:
      None

      Description

      The following code in DateVector is worrisome:

          @Override
          public DateTime getObject(int index) {
              org.joda.time.DateTime date = new org.joda.time.DateTime(get(index), org.joda.time.DateTimeZone.UTC);
              date = date.withZoneRetainFields(org.joda.time.DateTimeZone.getDefault());
              return date;
          }
      

      This code takes a date/time value stored in a value vector, converts it to UTC, then strips the time zone and replaces it with local time. The result it a "timestamp" in Java format (seconds since the epoch), but not really, it really the time since the epoch, as if the epoch had started in the local time zone rather than UTC.

      This is the kind of fun & games that people used to do in Java with the Date type before the advent of Joda time (and the migration of Joda into Java 8.)

      It is, in short, very bad practice and nearly impossible to get right.

      Further, converting a pure date (since this is a DateVector) into a date/time is fraught with peril. A date has no corresponding time. 1 AM on Friday in one time zone might be 11 PM on Thursday in another. Converting from dates to times is very difficult.

      If the DateVector corresponds to a date, then it should be simple date with no implied time zone and no implied relationship to time. If there is to be a mapping of time, it must be to a LocalTime (in Joda and Java 8) that has no implied time zone.

      Note that this code directly contradicts the statement in Drill documentation: "Drill stores values in Coordinated Universal Time (UTC)." Actually, even the documentation is questionable: what does it mean to store a date in UTC because of the above issues?

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              • Assignee:
                Unassigned
                Reporter:
                paul-rogers Paul Rogers
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                • Created:
                  Updated: