> If you have an external time source (or the hardware STP feature), this is
probably automatic.

So the time source "knows" about the local time change at 2 am and tells the
Z system? I guess I see that. ETRZONE YES "Specifies that the system is to
use the Sysplex Timer to set the time zone constant."

> all of the major subsystems (DB2, IMS, CICS, z/OS, Websphere, BMC...,
Compuware... CA,,, ) I am aware of need no intervention to handle the time
change.

I am the lead developer of such a system. Yes, we need "no intervention" but
I am trying to make sure we handle the local time change in the best way
possible. It's a tough thing to test "in real life" because the time change
only happens twice a year. It does not happen in these subsystems by magic;
it happens because someone coded the logic correctly. That's what I need to
make sure we do.

FWIW, we have no "logical" dependency on local time (e.g. like database
timestamps that control recovery logic) but (a.) some of our inputs are in
local time -- the SMF standard timestamp for a start -- and (b.) some of our
outputs either must be or may customer-configured to be in local time.

Do you know the answer to my question 2?

Charles

-----Original Message-----
From: IBM Mainframe Discussion List [mailto:IBM-MAIN@LISTSERV.UA.EDU] On
Behalf Of Allan Staller
Sent: Thursday, February 22, 2018 5:49 AM
To: IBM-MAIN@LISTSERV.UA.EDU
Subject: Re: Two summer time change questions

It depends.
If you have an external time source (or the hardware STP feature), this is
probably automatic. Check your CLOCKxx members in SYS1.PARMLIB.

The other alternative is to manually issue a SET TZ  command at the
appropriate time (either by automation or human).

For the record, all of the major subsystems (DB2, IMS, CICS, z/OS,
Websphere, BMC..., Compuware... CA,,, ) I am aware of need no intervention
to handle the time change.
The only remaining hurdle in most shops regarding time change is application
logic.

For the Spring time change there is usually no issue, for the Fall time
change, many shops go idle for 1 hour to prevent the possibility of
duplicate time stamps (based on local time).

HTH,

-----Original Message-----
From: IBM Mainframe Discussion List [mailto:IBM-MAIN@LISTSERV.UA.EDU] On
Behalf Of Charles Mills
Sent: Wednesday, February 21, 2018 6:46 PM
To: IBM-MAIN@LISTSERV.UA.EDU
Subject: Two summer time change questions

First though, apologies for asking what perhaps has been covered before --
perhaps even asked by me. I am having no luck searching the archives. I
search on CVTTZ and get no hits even though I have IBM-MAIN messages in my
own Outlook that contain CVTTZ.

1. Humor a guy with almost no operations experience with the world's most
newbie operations question. If you are a shop in North America, how will you
"convert" your z/OS instances to summer time next month? Do you or does your
console automation software have to enter a SET command, or does it happen
automagically internally to z/OS on some pre-configured schedule? (I
remember I had a P/390 back in the day and VM had an internal table that did
the time change automagically but I recall I had to re-IPL OS/390 to pick up
the change.)

2. When the above happens, will CVTTZ and CVTLDTO get updated on the fly? If
I inspected them one second would I see an offset of, e.g., 8 hours (in TOD
or "TOD-high word" format as appropriate) and if I inspected them a second
later I would see 7 hours?

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