Re: Daylight savings time confusion

On 3/15/2010 2:40 PM, Rob Richardson wrote:
> Greetings!
>
> Our database monitors the progression of steel coils through the
> annealing process. The times for each step are recorded in wallclock
> time (US eastern time zone for this customer) and in UTC time. During
> standard time, the difference will be 5 hours, and during daylight
> savings time the difference will be 4 hours.
>
> I just looked at the record for a charge for which heating started just
> after 9:00 Saturday night, less than 3 hours before the change to
> daylight savings time. The UTC time stored for this event is six hours
> later!
>
> The function that writes these times first stores the UTC time in a
> variable named UTCTimestamp:
>
> select into UTCTimestamp current_timestamp at time zone 'UTC';
>
> Then, later in the function, the two times get written into the record
> (along with some other stuff):
>
> update charge set
> status=ChargeStatus,fire_date=current_timestamp,
> fire_date_utc=UTCTimestamp, fire_user=FurnaceTender,
> updated_by=UserId,updated_date=current_timestamp where charge=ChargeNum;
>
> Can someone explain why fire_date is 2010-03-13 21:39:51.744 and
> fire_date_utc is 2010-03-14 03:39:51.744 for this record?
>
> There is another charge that began firing five and a half hours before
> the DST switch. The difference between its fire_date and fire_date_utc
> times is five hours, as expected.
>
> RobR
>

My first thought is the server is using libraries that don't know the
DST was brought forward 3 weeks earlier than last year, its clock is
all confused.

i would check the time on Postgresql Server making sure it read out
correctly. below was run on pg 8.4 windows 2008 server

Select current_timestamp, current_timestamp at time zone 'UTC';
"2010-03-15 16:43:11.382-04";"2010-03-15 20:43:11.382"

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