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Date: Mon, 5 Jun 2017 00:56:04 +0000 (UTC)
From: "Paul Rogers (JIRA)" <jira@apache.org>
To: dev@drill.apache.org
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Subject: [jira] [Created] (DRILL-5562) Vector types IntervalYear,
 IntervalDay and Interval are of the wrong width
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archived-at: Mon, 05 Jun 2017 00:56:11 -0000

Paul Rogers created DRILL-5562:
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             Summary: Vector types IntervalYear, IntervalDay and Interval are of the wrong width
                 Key: DRILL-5562
                 URL: https://issues.apache.org/jira/browse/DRILL-5562
             Project: Apache Drill
          Issue Type: Bug
    Affects Versions: 1.8.0
            Reporter: Paul Rogers


Drill provides three interval types, described in `ValueVectorTypes.tdd`:

* `IntervalYear`: a duration in months (sic)
* `IntervalDay`: a duration in days and ms.
* `Interval`: a duration in months, days and ms.

The file defines the width of each "field" (ms, days, months) as an int: 4 bytes. But, the total vector width is wrong:

* `IntervalYear`: 8 bytes (should be 4: for months)
* `IntervalDay`: 12 bytes (should be 8: for days and ms.)
* `Interval`: 16 bytes (should be 12: for months, days and ms.)

It could be that the extra 4 bytes is supposed to be for a time zone. But, time zones don't apply to intervals: an hour is the same duration everywhere on earth.

Since an interval does not contain a point in time, a time-zone is not useful even for daylight savings time adjustments.

The code for each type reflects the "missing" 4 bytes. For example, for the 12-byte `IntervalDay` vector:

{code}
    public void set(int index, int days, int milliseconds) {
      final int offsetIndex = index * VALUE_WIDTH;
      data.setInt(offsetIndex, days);
      data.setInt((offsetIndex + 4), milliseconds);
    }
{code}

Note also that the Drill IntervalDay need not be two fields wide. Except on a leap second, a day has a fixed number of milliseconds. And, the only way to compensate for a leap second is to know a point in time, which the interval does not have. Even if measured across a leap second, an interval of a minute is always 60 seconds. It is only when doing:

{code}
end date/time = start date/time + interval
{code}

is the leap second even needed.

Although the ISO format expresses intervals as a tuple of (year, month, day, hour, minute, second), the same value can be expressed as (months, ms) (with the proper conversions), so Drill's interval types need only be 4 and 8 bytes wide.


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