RE: Daylight Saving Time

V5R3

Denis Robitaille
Directeur services technique TI
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>>> bpiotrowski@xxxxxxxxxxxxxxx 2006-02-01 13:01:11 >>>
Can someone tell me at what level of O/S will perform an automatic
time
change based on DL savings?  We're running v5r2m0.  I currently have a
script that runs every Sunday to check whether or not it is to make
time
adjustments.

Thanks,

Brian.

-----Original Message-----
From: Bruce Vining [mailto:bvining@xxxxxxxxxx] 
Sent: Wednesday, February 01, 2006 11:51 AM
To: Midrange Systems Technical Discussion
Subject: Re: Daylight Saving Time

Jeff,

Changing your system time zone from QN0500EST2 to QN0500EST will cause
the
system to automatically recognize the start and end of DST.  As
shipped
by
IBM, DST will start at 2:00 local time on the first Sunday of April
and
end
at 2:00 local time on the last Sunday of October.

When DST starts local system time will change from 2:00 AM to 3:00 AM,
and
when ending from 2:00 AM to 1:00 AM.  This will take place independent
of
whether or not you are using an external time server, and will conform
to
your local definitions of time.

Time adjustment is not used when changing local time for DST.  Time
adjustment is used when a discrepancy is detected between the UTC time
sent
by the time server and the local UTC time maintained by the system.

Time adjustment is not used as that would cause the minute after 2:00
AM
to
be "something" between 2:00AM and 3:00AM.  This time value (for
example
purposes 2:01AM) does not exist (per your legislative authorities).
What
would the system convert that time to if you wanted to convert to
Mountain
time?  What would an auditor say if a change was made at 2:01AM?
Likewise
a time value 2:01 after DST ended would imply an hour and a minute
past
the
DST time shift, not just one minute.

Users could use the time adjustment feature of the system to
circumvent
this time shift for DST, but the system DST support is not going to
start
recording 'non-existent' time stamps -- you'll have to explain this
time
values yourself.  And using time adjustment by itself to make DST
changes
(leaving the time zone unchanged) will cause discrepancies in the UTC
offset the system believes it's working in.

It is because of these types of headaches that the system internally
tracks
time with UTC (rather than local time) starting with V5R3.  UTC does
not
have the concept of DST.  Time simply moves forward, and the system
then
converts the internal UTC times to the appropriate local times based
on
the
time zone in effect.  To avoid time shifts the use of a standard such
as
UTC is the way to go.  Local times are just too easily changed by
government decisions.

Bruce Vining



 

             "Jeff Crosby"

             <jlcrosby@dilgard

             foods.com>
To 
             Sent by:                  "'Midrange Systems Technical

             midrange-l-bounce         Discussion'"

             s@xxxxxxxxxxxx            <midrange-l@xxxxxxxxxxxx>

 
cc 
 

             02/01/2006 09:02
Subject 
             AM                        Daylight Saving Time

 

 

             Please respond to

             Midrange Systems

                 Technical

                Discussion

             <midrange-l@midra

                 nge.com>

 

 





I have never had to be concerned with this in the past, but the
Indiana
legislature has now decreed that Indiana will begin observing DST this
year.

With the new time zone and especially time adjustment stuff available
in
V5R3, I thought it would be simple:  change the system value QTIMZON
from
QN0500EST2 to QN0500EST, the system will automajically start adjusting
time
before DST starts/ends, and I'm good to go, but it doesn't look that
simple.

It doesn't look like 'time adjustment' takes place automatically at
DST
start/end at all.  What I think happens is that because my i5 checks
with
an
external time server every hour, the time will change in one fell
swoop.
If
I _don't_ check with an external time server, it won't take place at
all.

Assuming I have already changed to time zone QN0500EST, it sounds like
I
need to:

1) On the Saturday before DST starts/ends, tell the i5 to stop
checking
externally for the time.

2) Start a time adjustment either forward (spring) or backward (fall)
1
hour.

3) On Monday, tell the i5 to start checking externally for the time
again.

Am I right?  Or missing something simple?

Thanks and I'll be moving to Arizona.

--
Jeff Crosby
Dilgard Frozen Foods, Inc.
P.O. Box 13369
Ft. Wayne, IN 46868-3369
260-422-7531

The opinions expressed are my own and not necessarily the opinion of
my
company.  Unless I say so.


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