Thanks all. Yes, I'm well aware of the points that Skip and Allan make. Question one was mostly curiosity. What I really needed to understand was the "timeliness" of CVTLDTO and I have that now, thanks to an off-list reply. (Yes, it is updated immediately when the local offset is changed, either by command or by the ETR.)
Charles -----Original Message----- From: IBM Mainframe Discussion List [mailto:[email protected]] On Behalf Of Jesse 1 Robinson Sent: Thursday, February 22, 2018 2:02 PM To: [email protected] Subject: Re: Two summer time change questions The most important question is whether your LPAR(s) are running with true GMT/UTC. It was once customary for shops to set both GMT and Local time to a nearby wall clock and specify zero Local offset. Over time most shops have hopped on to the straight and narrow path by defining GMT as UTC with a Local offset that either varies (or does not) by season. If you using a true offset value, you can use 'some timer facility' to adjust the offset twice a year. For us that was once the external sysplex timer (9037). Now it's built-in STP (Server Time Protocol) that performs the time change operation--automatically if desired. An IPL is not necessary for z/OS. Otherwise you can issue the SET CLOCK command. However, that changes only the running system. Any desired change to 'parm' fields would have to be done manually. Again, an IPL is not necessary for z/OS. As others have said, most modern software like CICS and DB2 logs in UTC, so changes to Local time don't matter except to Bioware. The one-hour overlap when 'falling back' is not a problem except for people reading syslog or operlog, where duplicate time stamps will appear. I'm quite sure that a multiplex requires some kind of hardware timer because XCF cannot handle differing time stamps among members. . . J.O.Skip Robinson Southern California Edison Company Electric Dragon Team Paddler SHARE MVS Program Co-Manager 323-715-0595 Mobile 626-543-6132 Office ⇐=== NEW [email protected] -----Original Message----- From: IBM Mainframe Discussion List [mailto:[email protected]] On Behalf Of Allan Staller Sent: Thursday, February 22, 2018 5:49 AM To: [email protected] Subject: (External):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:[email protected]] On Behalf Of Charles Mills Sent: Wednesday, February 21, 2018 6:46 PM To: [email protected] 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? ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
