[DRILL-5332] DateVector support uses questionable conversions to a time

• Type: Bug
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Affects Version/s: 1.9.0
• Assignee: Unassigned
• Reporter: Paul Rogers
• Created: 08/Mar/17 05:29
• Updated: 29/Oct/18 14:20

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?

Issue Links

• contains: DRILL-5141 Difference in output date format on sqlline vs Drill's Web UI
• relates to: DRILL-4060 CTAS to csv or json files gives incorrect time values
• relates to: DRILL-5334 Questionable code in the TimeVector class
• relates to: DRILL-6242 Output format for nested date, time, timestamp values in an object hierarchy
• relates to: DRILL-5002 Using hive's date functions on top of date column gives wrong results for local time-zone