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From "Paul Rogers (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (DRILL-5332) DateVector support uses questionable conversions to a time
Date Wed, 08 Mar 2017 05:33:43 GMT

     [ https://issues.apache.org/jira/browse/DRILL-5332?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Paul Rogers updated DRILL-5332:
-------------------------------
    Description: 
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?

  was:
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.


> 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
>
> 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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