RE: Daylight Saving Time

                                                                           
             "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 11:54                                      Subject 
             AM                        RE: Daylight Saving Time            
                                                                           
                                                                           
             Please respond to                                             
             Midrange Systems                                              
                 Technical                                                 
                Discussion                                                 
             <midrange-l@midra                                             
                 nge.com>                                                  
                                                                           
                                                                           







>> 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.

>I understood all that.  I was looking for something that speeded it up to
>move ahead an hour, or slowed it down for an hour catch-up instead of a
jump
>in one fell swoop.  There is a lot of discussion in the Infocenter (yes I
>found it!) regarding changing the time and it's effect on scheduled jobs
and
>other time-dependant operations.

>> 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).

>OK, I never thought of the time 'not existing' for legal reasons.  But
what
>about the other direction in the fall?  Does the time 1:30am legally occur
>twice?

1:30 AM does indeed occur twice.  Once for 1:30 AM EDT and once for 1:30 AM
EST.  Unfortunately most applications don't currently present the
applicable time zone name (or abbreviation in my example) so 1:30AM is
ambiguous when shifting to standard time.  The names and abbreviation can
be seen by looking at QN0500EST.

>> 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.

>Does that mean UTC is what goes into QHST?  Does that mean if I view QHST,
>then change my time zone or offset, then view QHST again, the times will
be
>different?

In V5R3 and V5R4 QHST continues to use local system time.  I would not be
surprised though to see this change in a future release.  If at some point
in the future the system allowed each job to run in it's own time zone and
QHST normalized the messages to UTC then yes, one user may see the QHST
entry in New Zealand time, another user the same entry in Eastern US time.

>And how does the Advanced Job Scheduler know not to run that 1:30am
>scheduled job a 2nd time?  Or does it run again?  (No, I don't have any
>between 1am and 3am, but inquiring minds want to know.)

I'm not familiar enough with the Advanced Job Scheduler to say for sure,
but the i5/OS provided scheduler would run the job once -- for the first
1:30AM (assuming you're doing absolute time of day submissions).

Bruce Vining

--
This is the Midrange Systems Technical Discussion (MIDRANGE-L) mailing list
To post a message email: MIDRANGE-L@xxxxxxxxxxxx
To subscribe, unsubscribe, or change list options,
visit: http://lists.midrange.com/mailman/listinfo/midrange-l
or email: MIDRANGE-L-request@xxxxxxxxxxxx
Before posting, please take a moment to review the archives
at http://archive.midrange.com/midrange-l.