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https://issues.apache.org/jira/browse/DRILL-5332?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16667275#comment-16667275
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Bohdan Kazydub commented on DRILL-5332:
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It should be noted that while there was a change for reading date type values
(now using java.time package) shown by [~vitalii] there still are functions
(generated by ToDateTypeFunctions and SqlToDateTypeFunctions templates at
least) that write this values using Joda-time (org.joda.time).
> DateVector support uses questionable conversions to a time
> ----------------------------------------------------------
>
> Key: DRILL-5332
> URL: https://issues.apache.org/jira/browse/DRILL-5332
> Project: Apache Drill
> Issue Type: Bug
> Affects Versions: 1.9.0
> Reporter: Paul Rogers
> Priority: Major
>
> The following code in {{DateVector}} is worrisome:
> {code}
> @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;
> }
> {code}
> 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|http://drill.apache.org/docs/date-time-and-timestamp/]: "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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